diff --git a/blog/2016/03/24/introducing-hot-reloading.html b/blog/2016/03/24/introducing-hot-reloading.html index 6ece2a8238a..c226efa172d 100644 --- a/blog/2016/03/24/introducing-hot-reloading.html +++ b/blog/2016/03/24/introducing-hot-reloading.html @@ -69,7 +69,7 @@ export default function } return store; -};

When you change a reducer, the code to accept that reducer will be sent to the client. Then the client will realize that the reducer doesn't know how to accept itself, so it will look for all the modules that refer it and try to accept them. Eventually, the flow will get to the single store, the configureStore module, which will accept the HMR update.

Conclusion #

If you are interested in helping making hot reloading better, I encourage you to read Dan Abramov's post around the future of hot reloading and to contribute. For example, Johny Days is going to make it work with multiple connected clients. We're relying on you all to maintain and improve this feature.

With React Native, we have the opportunity to rethink the way we build apps in order to make it a great developer experience. Hot reloading is only one piece of the puzzle, what other crazy hacks can we do to make it better?

React Nativenext
React Native Blog
Stay up-to-date with the latest React Native news and events.

Héctor Ramos —

San Francisco Meetup Recap

Last week I had the opportunity to attend the React Native Meetup at Zynga’s San Francisco office. With around 200 people in attendance, it served as a great place to meet other developers near me that are also interested in React Native.

I was particularly interested in learning more about how React and React Native are used at companies like Zynga, Netflix, and Airbnb. The agenda for the night would be as follows:

  • Rapid Prototyping in React
  • Designing APIs for React Native
  • Bridging the Gap: Using React Native in Existing Codebases

But first, the event started off with a quick introduction and a brief recap of recent news:

If one of these meetups is held near you, I highly recommend attending!

Rapid Prototyping in React at Zynga #

The first round of news was followed by a quick introduction by Zynga, our hosts for the evening. Abhishek Chadha talked about how they use React to quickly prototype new experiences on mobile, demoing a quick prototype of a Draw Something-like app. They use a similar approach as React Native, providing access to native APIs via a bridge. This was demonstrated when Abhishek used the device's camera to snap a photo of the audience and then drew a hat on someone's head.

Designing APIs for React Native at Netflix #

Up next, the first featured talk of the evening. Clarence Leung, Senior Software Engineer at Netflix, presented his talk on Designing APIs for React Native. First he noted the two main types of libraries one may work on: components such as tab bars and date pickers, and libraries that provide access to native services such as the camera roll or in-app payments. There are two ways one may approach when building a library for use in React Native:

  • Provide platform-specific components
  • A cross-platform library with a similar API for both iOS and Android

Each approach has its own considerations, and it’s up to you to determine what works best for your needs.

Approach #1

As an example of platform-specific components, Clarence talked about the DatePickerIOS and DatePickerAndroid from core React Native. On iOS, date pickers are rendered as part of the UI and can be easily embedded in an existing view, while date pickers on Android are presented modally. It makes sense to provide separate components in this case.

Approach #2

Photo pickers, on the other hand, are treated similarly on iOS and Android. There are some slight differences — Android does not group photos into folders like iOS does with Selfies, for example — but those are easily handled using if statements and the Platform component.

Regardless of which approach you settle on, it’s a good idea to minimize the API surface and build app-specific libraries. For example, iOS’s In-App Purchase framework supports one-time, consumable purchases, as well as renewable subscriptions. If your app will only need to support consumable purchases, you may get away with dropping support for subscriptions in your cross-platform library.

There was a brief Q&A session at the end of Clarence’s talk. One of the interesting tid bits that came out of it was that around 80% of the React Native code written for these libraries at Netflix is shared across both iOS and Android.

Bridging the Gap, Using React Native in Existing Codebases #

The final talk of the night was by Leland Richardson from Airbnb. The talk was focused on the use of React Native in existing codebases. I already know how easy it is to write a new app from scratch using React Native, so I was very interested to hear about Airbnb’s experience adopting React Native in their existing native apps.

Leland started off by talking about greenfield apps versus brownfield apps. Greenfield means to start a project without the need to consider any prior work. This is in contrast to brownfield projects where you need to take into account the existing project’s requirements, development processes, and all of the teams various needs.

When you’re working on a greenfield app, the React Native CLI sets up a single repository for both iOS and Android and everything just works. The first challenge against using React Native at Airbnb was the fact that the iOS and Android app each had their own repository. Multi-repo companies have some hurdles to get past before they can adopt React Native.

To get around this, Airbnb first set up a new repo for the React Native codebase. They used their continuous integration servers to mirror the iOS and Android repos into this new repo. After tests are run and the bundle is built, the build artifacts are synced back to the iOS and Android repos. This allows the mobile engineers to work on native code without altering their development enviroment. Mobile engineers don't need to install npm, run the packager, or remember to build the JavaScript bundle. The engineers writing actual React Native code do not have to worry about syncing their code across iOS and Android, as they work on the React Native repository directly.

This does come with some drawbacks, mainly they could not ship atomic updates. Changes that require a combination of native and JavaScript code would require three separate pull requests, all of which had to be carefully landed. In order to avoid conflicts, CI will fail to land changes back to the iOS and Android repos if master has changed since the build started. This would cause long delays during high commit frequency days (such as when new releases are cut).

Airbnb has since moved to a mono repo approach. Fortunately this was already under consideration, and once the iOS and Android teams became comfortable with using React Native they were happy to accelerate the move towards the mono repo.

This has solved most of the issues they had with the split repo approach. Leland did note that this does cause a higher strain on the version control servers, which may be an issue for smaller companies.

The Navigation Problem #

The second half of Leland's talk focused on a topic that is dear to me: the Navigation problem in React Native. He talked about the abundance of navigation libraries in React Native, both first party and third party. NavigationExperimental was mentioned as something that seemed promising, but ended up not being well suited for their use case.

In fact, none of the existing navigation libraries seem to work well for brownfield apps. A brownfield app requires that the navigation state be fully owned by the native app. For example, if a user’s session expires while a React Native view is being presented, the native app should be able to take over and present a login screen as needed.

Airbnb also wanted to avoid replacing native navigation bars with JavaScript versions as part of a transition, as the effect could be jarring. Initially they limited themselves to modally presented views, but this obviously presented a problem when it came to adopting React Native more widely within their apps.

They decided that they needed their own library. The library is called airbnb-navigation. The library has not yet being open sourced as it is strongly tied to Airbnb’s codebase, but it is something they’d like to release by the end of the year.

I won’t go into much detail into the library’s API, but here are some of the key takeaways:

  • One must preregister scenes ahead of time
  • Each scene is displayed within its own RCTRootView. They are presented natively on each platform (e.g. UINavigationControllers are used on iOS).
  • The main ScrollView in a scene should be wrapped in a ScrollScene component. Doing so allows you to take advantage of native behaviors such as tapping on the status bar to scroll to the top on iOS.
  • Transitions between scenes are handled natively, no need to worry about performance.
  • The Android back button is automatically supported.
  • They can take advantage of View Controller based navigation bar styling via a Navigator.Config UI-less component.

There’s also some considerations to keep in mind:

  • The navigation bar is not easily customized in JavaScript, as it is a native component. This is intentional, as using native navigation bars is a hard requirement for this type of library.
  • ScreenProps must be serialized/de-serialized whenever they're sent through the bridge, so care must be taken if sending too much data here.
  • Navigation state is owned by the native app (also a hard requirement for the library), so things like Redux cannot manipulate navigation state.

Leland's talk was also followed by a Q&A session. Overall, Airbnb is satisfied with React Native. They’re interested in using Code Push to fix any issues without going through the App Store, and their engineers love Live Reload, as they don't have to wait for the native app to be rebuilt after every minor change.

Closing Remarks #

The event ended with some additional React Native news:

Meetups provide a good opportunity to meet and learn from other developers in the community. I'm looking forward to attending more React Native meetups in the future. If you make it up to one of these, please look out for me and let me know how we can make React Native work better for you!

React Nativenext
React Native Blog
Stay up-to-date with the latest React Native news and events.

Héctor Ramos —

San Francisco Meetup Recap

Last week I had the opportunity to attend the React Native Meetup at Zynga’s San Francisco office. With around 200 people in attendance, it served as a great place to meet other developers near me that are also interested in React Native.

I was particularly interested in learning more about how React and React Native are used at companies like Zynga, Netflix, and Airbnb. The agenda for the night would be as follows:

  • Rapid Prototyping in React
  • Designing APIs for React Native
  • Bridging the Gap: Using React Native in Existing Codebases

But first, the event started off with a quick introduction and a brief recap of recent news:

If one of these meetups is held near you, I highly recommend attending!

Rapid Prototyping in React at Zynga #

The first round of news was followed by a quick introduction by Zynga, our hosts for the evening. Abhishek Chadha talked about how they use React to quickly prototype new experiences on mobile, demoing a quick prototype of a Draw Something-like app. They use a similar approach as React Native, providing access to native APIs via a bridge. This was demonstrated when Abhishek used the device's camera to snap a photo of the audience and then drew a hat on someone's head.

Designing APIs for React Native at Netflix #

Up next, the first featured talk of the evening. Clarence Leung, Senior Software Engineer at Netflix, presented his talk on Designing APIs for React Native. First he noted the two main types of libraries one may work on: components such as tab bars and date pickers, and libraries that provide access to native services such as the camera roll or in-app payments. There are two ways one may approach when building a library for use in React Native:

  • Provide platform-specific components
  • A cross-platform library with a similar API for both iOS and Android

Each approach has its own considerations, and it’s up to you to determine what works best for your needs.

Approach #1

As an example of platform-specific components, Clarence talked about the DatePickerIOS and DatePickerAndroid from core React Native. On iOS, date pickers are rendered as part of the UI and can be easily embedded in an existing view, while date pickers on Android are presented modally. It makes sense to provide separate components in this case.

Approach #2

Photo pickers, on the other hand, are treated similarly on iOS and Android. There are some slight differences — Android does not group photos into folders like iOS does with Selfies, for example — but those are easily handled using if statements and the Platform component.

Regardless of which approach you settle on, it’s a good idea to minimize the API surface and build app-specific libraries. For example, iOS’s In-App Purchase framework supports one-time, consumable purchases, as well as renewable subscriptions. If your app will only need to support consumable purchases, you may get away with dropping support for subscriptions in your cross-platform library.

There was a brief Q&A session at the end of Clarence’s talk. One of the interesting tid bits that came out of it was that around 80% of the React Native code written for these libraries at Netflix is shared across both iOS and Android.

Bridging the Gap, Using React Native in Existing Codebases #

The final talk of the night was by Leland Richardson from Airbnb. The talk was focused on the use of React Native in existing codebases. I already know how easy it is to write a new app from scratch using React Native, so I was very interested to hear about Airbnb’s experience adopting React Native in their existing native apps.

Leland started off by talking about greenfield apps versus brownfield apps. Greenfield means to start a project without the need to consider any prior work. This is in contrast to brownfield projects where you need to take into account the existing project’s requirements, development processes, and all of the teams various needs.

When you’re working on a greenfield app, the React Native CLI sets up a single repository for both iOS and Android and everything just works. The first challenge against using React Native at Airbnb was the fact that the iOS and Android app each had their own repository. Multi-repo companies have some hurdles to get past before they can adopt React Native.

To get around this, Airbnb first set up a new repo for the React Native codebase. They used their continuous integration servers to mirror the iOS and Android repos into this new repo. After tests are run and the bundle is built, the build artifacts are synced back to the iOS and Android repos. This allows the mobile engineers to work on native code without altering their development enviroment. Mobile engineers don't need to install npm, run the packager, or remember to build the JavaScript bundle. The engineers writing actual React Native code do not have to worry about syncing their code across iOS and Android, as they work on the React Native repository directly.

This does come with some drawbacks, mainly they could not ship atomic updates. Changes that require a combination of native and JavaScript code would require three separate pull requests, all of which had to be carefully landed. In order to avoid conflicts, CI will fail to land changes back to the iOS and Android repos if master has changed since the build started. This would cause long delays during high commit frequency days (such as when new releases are cut).

Airbnb has since moved to a mono repo approach. Fortunately this was already under consideration, and once the iOS and Android teams became comfortable with using React Native they were happy to accelerate the move towards the mono repo.

This has solved most of the issues they had with the split repo approach. Leland did note that this does cause a higher strain on the version control servers, which may be an issue for smaller companies.

The Navigation Problem #

The second half of Leland's talk focused on a topic that is dear to me: the Navigation problem in React Native. He talked about the abundance of navigation libraries in React Native, both first party and third party. NavigationExperimental was mentioned as something that seemed promising, but ended up not being well suited for their use case.

In fact, none of the existing navigation libraries seem to work well for brownfield apps. A brownfield app requires that the navigation state be fully owned by the native app. For example, if a user’s session expires while a React Native view is being presented, the native app should be able to take over and present a login screen as needed.

Airbnb also wanted to avoid replacing native navigation bars with JavaScript versions as part of a transition, as the effect could be jarring. Initially they limited themselves to modally presented views, but this obviously presented a problem when it came to adopting React Native more widely within their apps.

They decided that they needed their own library. The library is called airbnb-navigation. The library has not yet being open sourced as it is strongly tied to Airbnb’s codebase, but it is something they’d like to release by the end of the year.

I won’t go into much detail into the library’s API, but here are some of the key takeaways:

  • One must preregister scenes ahead of time
  • Each scene is displayed within its own RCTRootView. They are presented natively on each platform (e.g. UINavigationControllers are used on iOS).
  • The main ScrollView in a scene should be wrapped in a ScrollScene component. Doing so allows you to take advantage of native behaviors such as tapping on the status bar to scroll to the top on iOS.
  • Transitions between scenes are handled natively, no need to worry about performance.
  • The Android back button is automatically supported.
  • They can take advantage of View Controller based navigation bar styling via a Navigator.Config UI-less component.

There’s also some considerations to keep in mind:

  • The navigation bar is not easily customized in JavaScript, as it is a native component. This is intentional, as using native navigation bars is a hard requirement for this type of library.
  • ScreenProps must be serialized/de-serialized whenever they're sent through the bridge, so care must be taken if sending too much data here.
  • Navigation state is owned by the native app (also a hard requirement for the library), so things like Redux cannot manipulate navigation state.

Leland's talk was also followed by a Q&A session. Overall, Airbnb is satisfied with React Native. They’re interested in using Code Push to fix any issues without going through the App Store, and their engineers love Live Reload, as they don't have to wait for the native app to be rebuilt after every minor change.

Closing Remarks #

The event ended with some additional React Native news:

Meetups provide a good opportunity to meet and learn from other developers in the community. I'm looking forward to attending more React Native meetups in the future. If you make it up to one of these, please look out for me and let me know how we can make React Native work better for you!

React Nativenext
React Native Blog
Stay up-to-date with the latest React Native news and events.
React Nativenext
React Native Blog
Stay up-to-date with the latest React Native news and events.
React Nativenext
React Native Blog
Stay up-to-date with the latest React Native news and events.

Héctor Ramos —

San Francisco Meetup Recap

Last week I had the opportunity to attend the React Native Meetup at Zynga’s San Francisco office. With around 200 people in attendance, it served as a great place to meet other developers near me that are also interested in React Native.

Kevin Lacker —

Toward Better Documentation

Part of having a great developer experience is having great documentation. A lot goes into creating good docs - the ideal documentation is concise, helpful, accurate, complete, and delightful. Recently we've been working hard to make the docs better based on your feedback, and we wanted to share some of the improvements we've made.

Martín Bigio —

Introducing Hot Reloading

React Native's goal is to give you the best possible developer experience. A big part of it is the time it takes between you save a file and be able to see the changes. Our goal is to get this feedback loop to be under 1 second, even as your app grows.

React Nativenext
React Native Blog
Stay up-to-date with the latest React Native news and events.

Héctor Ramos —

San Francisco Meetup Recap

Last week I had the opportunity to attend the React Native Meetup at Zynga’s San Francisco office. With around 200 people in attendance, it served as a great place to meet other developers near me that are also interested in React Native.

Kevin Lacker —

Toward Better Documentation

Part of having a great developer experience is having great documentation. A lot goes into creating good docs - the ideal documentation is concise, helpful, accurate, complete, and delightful. Recently we've been working hard to make the docs better based on your feedback, and we wanted to share some of the improvements we've made.

Martín Bigio —

Introducing Hot Reloading

React Native's goal is to give you the best possible developer experience. A big part of it is the time it takes between you save a file and be able to see the changes. Our goal is to get this feedback loop to be under 1 second, even as your app grows.

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Profiling Android UI Performance #

We try our best to deliver buttery-smooth UI performance by default, but sometimes that just isn't possible. Remember, Android supports 10k+ different phones and is generalized to support software rendering: the framework architecture and need to generalize across many hardware targets unfortunately means you get less for free relative to iOS. But sometimes, there are things you can improve (and many times it's not native code's fault at all!).

The first step for debugging this jank is to answer the fundamental question of where your time is being spent during each 16ms frame. For that, we'll be using a standard Android profiling tool called systrace. But first...

Make sure that JS dev mode is OFF!

You should see __DEV__ === false, development-level warning are OFF, performance optimizations are ON in your application logs (which you can view using adb logcat)

Profiling with Systrace #

Systrace is a standard Android marker-based profiling tool (and is installed when you install the Android platform-tools package). Profiled code blocks are surrounded by markers start/end markers which are then visualized in a colorful chart format. Both the Android SDK and React Native framework provide standard markers that you can visualize.

Collecting a trace #

NOTE:

Systrace support was added in react-native v0.15. You will need to build with that version to collect a trace.

First, connect a device that exhibits the stuttering you want to investigate to your computer via USB and get it to the point right before the navigation/animation you want to profile. Run systrace as follows

$ <path_to_android_sdk>/platform-tools/systrace/systrace.py --time=10 -o trace.html sched gfx view -a <your_package_name>

A quick breakdown of this command:

  • time is the length of time the trace will be collected in seconds
  • sched, gfx, and view are the android SDK tags (collections of markers) we care about: sched gives you information about what's running on each core of your phone, gfx gives you graphics info such as frame boundaries, and view gives you information about measure, layout, and draw passes
  • -a <your_package_name> enables app-specific markers, specifically the ones built into the React Native framework. your_package_name can be found in the AndroidManifest.xml of your app and looks like com.example.app

Once the trace starts collecting, perform the animation or interaction you care about. At the end of the trace, systrace will give you a link to the trace which you can open in your browser.

Reading the trace #

After opening the trace in your browser (preferably Chrome), you should see something like this:

Example

If your trace .html file isn't opening correctly, check your browser console for the following:

ObjectObserveError

Since Object.observe was deprecated in recent browsers, you may have to open the file from the Google Chrome Tracing tool. You can do so by:

  • Opening tab in chrome chrome://tracing
  • Selecting load
  • Selecting the html file generated from the previous command.

HINT: Use the WASD keys to strafe and zoom

Enable VSync highlighting #

The first thing you should do is highlight the 16ms frame boundaries if you haven't already done that. Check this checkbox at the top right of the screen:

Enable VSync Highlighting

You should see zebra stripes as in the screenshot above. If you don't, try profiling on a different device: Samsung has been known to have issues displaying vsyncs while the Nexus series is generally pretty reliable.

Find your process #

Scroll until you see (part of) the name of your package. In this case, I was profiling com.facebook.adsmanager, which shows up as book.adsmanager because of silly thread name limits in the kernel.

On the left side, you'll see a set of threads which correspond to the timeline rows on the right. There are three/four threads we care about for our purposes: the UI thread (which has your package name or the name UI Thread), mqt_js and mqt_native_modules. If you're running on Android 5+, we also care about the Render Thread.

UI Thread #

This is where standard android measure/layout/draw happens. The thread name on the right will be your package name (in my case book.adsmanager) or UI Thread. The events that you see on this thread should look something like this and have to do with Choreographer, traversals, and DispatchUI:

UI Thread Example

JS Thread #

This is where JS is executed. The thread name will be either mqt_js or <...> depending on how cooperative the kernel on your device is being. To identify it if it doesn't have a name, look for things like JSCall, Bridge.executeJSCall, etc:

JS Thread Example

Native Modules Thread #

This is where native module calls (e.g. the UIManager) are executed. The thread name will be either mqt_native_modules or <...>. To identify it in the latter case, look for things like NativeCall, callJavaModuleMethod, and onBatchComplete:

Native Modules Thread Example

Bonus: Render Thread #

If you're using Android L (5.0) and up, you will also have a render thread in your application. This thread generates the actual OpenGL commands used to draw your UI. The thread name will be either RenderThread or <...>. To identify it in the latter case, look for things like DrawFrame and queueBuffer:

Render Thread Example

Identifying a culprit #

A smooth animation should look something like the following:

Smooth Animation

Each change in color is a frame -- remember that in order to display a frame, all our UI work needs to be done by the end of that 16ms period. Notice that no thread is working close to the frame boundary. An application rendering like this is rendering at 60FPS.

If you noticed chop, however, you might see something like this:

Choppy Animation from JS

Notice that the JS thread is executing basically all the time, and across frame boundaries! This app is not rendering at 60FPS. In this case, the problem lies in JS.

You might also see something like this:

Choppy Animation from UI

In this case, the UI and render threads are the ones that have work crossing frame boundaries. The UI that we're trying to render on each frame is requiring too much work to be done. In this case, the problem lies in the native views being rendered.

At this point, you'll have some very helpful information to inform your next steps.

JS Issues #

If you identified a JS problem, look for clues in the specific JS that you're executing. In the scenario above, we see RCTEventEmitter being called multiple times per frame. Here's a zoom-in of the JS thread from the trace above:

Too much JS

This doesn't seem right. Why is it being called so often? Are they actually different events? The answers to these questions will probably depend on your product code. And many times, you'll want to look into shouldComponentUpdate.

TODO: Add more tools for profiling JS

Native UI Issues #

If you identified a native UI problem, there are usually two scenarios:

  1. the UI you're trying to draw each frame involves to much work on the GPU, or
  2. You're constructing new UI during the animation/interaction (e.g. loading in new content during a scroll).

Too much GPU work #

In the first scenario, you'll see a trace that has the UI thread and/or Render Thread looking like this:

Overloaded GPU

Notice the long amount of time spent in DrawFrame that crosses frame boundaries. This is time spent waiting for the GPU to drain its command buffer from the previous frame.

To mitigate this, you should:

  • investigate using renderToHardwareTextureAndroid for complex, static content that is being animated/transformed (e.g. the Navigator slide/alpha animations)
  • make sure that you are not using needsOffscreenAlphaCompositing, which is disabled by default, as it greatly increases the per-frame load on the GPU in most cases.

If these don't help and you want to dig deeper into what the GPU is actually doing, you can check out Tracer for OpenGL ES.

Creating new views on the UI thread #

In the second scenario, you'll see something more like this:

Creating Views

Notice that first the JS thread thinks for a bit, then you see some work done on the native modules thread, followed by an expensive traversal on the UI thread.

There isn't an easy way to mitigate this unless you're able to postpone creating new UI until after the interaction, or you are able to simplify the UI you're creating. The react native team is working on a infrastructure level solution for this that will allow new UI to be created and configured off the main thread, allowing the interaction to continue smoothly.

Still stuck? #

If you are confused or stuck, please post ask on Stack Overflow with the react-native tag. If you are unable to get a response there, or find an issue with a core component, please File a Github issue.

← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Profiling Android UI Performance #

We try our best to deliver buttery-smooth UI performance by default, but sometimes that just isn't possible. Remember, Android supports 10k+ different phones and is generalized to support software rendering: the framework architecture and need to generalize across many hardware targets unfortunately means you get less for free relative to iOS. But sometimes, there are things you can improve (and many times it's not native code's fault at all!).

The first step for debugging this jank is to answer the fundamental question of where your time is being spent during each 16ms frame. For that, we'll be using a standard Android profiling tool called systrace. But first...

Make sure that JS dev mode is OFF!

You should see __DEV__ === false, development-level warning are OFF, performance optimizations are ON in your application logs (which you can view using adb logcat)

Profiling with Systrace #

Systrace is a standard Android marker-based profiling tool (and is installed when you install the Android platform-tools package). Profiled code blocks are surrounded by markers start/end markers which are then visualized in a colorful chart format. Both the Android SDK and React Native framework provide standard markers that you can visualize.

Collecting a trace #

NOTE:

Systrace support was added in react-native v0.15. You will need to build with that version to collect a trace.

First, connect a device that exhibits the stuttering you want to investigate to your computer via USB and get it to the point right before the navigation/animation you want to profile. Run systrace as follows

$ <path_to_android_sdk>/platform-tools/systrace/systrace.py --time=10 -o trace.html sched gfx view -a <your_package_name>

A quick breakdown of this command:

  • time is the length of time the trace will be collected in seconds
  • sched, gfx, and view are the android SDK tags (collections of markers) we care about: sched gives you information about what's running on each core of your phone, gfx gives you graphics info such as frame boundaries, and view gives you information about measure, layout, and draw passes
  • -a <your_package_name> enables app-specific markers, specifically the ones built into the React Native framework. your_package_name can be found in the AndroidManifest.xml of your app and looks like com.example.app

Once the trace starts collecting, perform the animation or interaction you care about. At the end of the trace, systrace will give you a link to the trace which you can open in your browser.

Reading the trace #

After opening the trace in your browser (preferably Chrome), you should see something like this:

Example

If your trace .html file isn't opening correctly, check your browser console for the following:

ObjectObserveError

Since Object.observe was deprecated in recent browsers, you may have to open the file from the Google Chrome Tracing tool. You can do so by:

  • Opening tab in chrome chrome://tracing
  • Selecting load
  • Selecting the html file generated from the previous command.

HINT: Use the WASD keys to strafe and zoom

Enable VSync highlighting #

The first thing you should do is highlight the 16ms frame boundaries if you haven't already done that. Check this checkbox at the top right of the screen:

Enable VSync Highlighting

You should see zebra stripes as in the screenshot above. If you don't, try profiling on a different device: Samsung has been known to have issues displaying vsyncs while the Nexus series is generally pretty reliable.

Find your process #

Scroll until you see (part of) the name of your package. In this case, I was profiling com.facebook.adsmanager, which shows up as book.adsmanager because of silly thread name limits in the kernel.

On the left side, you'll see a set of threads which correspond to the timeline rows on the right. There are three/four threads we care about for our purposes: the UI thread (which has your package name or the name UI Thread), mqt_js and mqt_native_modules. If you're running on Android 5+, we also care about the Render Thread.

UI Thread #

This is where standard android measure/layout/draw happens. The thread name on the right will be your package name (in my case book.adsmanager) or UI Thread. The events that you see on this thread should look something like this and have to do with Choreographer, traversals, and DispatchUI:

UI Thread Example

JS Thread #

This is where JS is executed. The thread name will be either mqt_js or <...> depending on how cooperative the kernel on your device is being. To identify it if it doesn't have a name, look for things like JSCall, Bridge.executeJSCall, etc:

JS Thread Example

Native Modules Thread #

This is where native module calls (e.g. the UIManager) are executed. The thread name will be either mqt_native_modules or <...>. To identify it in the latter case, look for things like NativeCall, callJavaModuleMethod, and onBatchComplete:

Native Modules Thread Example

Bonus: Render Thread #

If you're using Android L (5.0) and up, you will also have a render thread in your application. This thread generates the actual OpenGL commands used to draw your UI. The thread name will be either RenderThread or <...>. To identify it in the latter case, look for things like DrawFrame and queueBuffer:

Render Thread Example

Identifying a culprit #

A smooth animation should look something like the following:

Smooth Animation

Each change in color is a frame -- remember that in order to display a frame, all our UI work needs to be done by the end of that 16ms period. Notice that no thread is working close to the frame boundary. An application rendering like this is rendering at 60FPS.

If you noticed chop, however, you might see something like this:

Choppy Animation from JS

Notice that the JS thread is executing basically all the time, and across frame boundaries! This app is not rendering at 60FPS. In this case, the problem lies in JS.

You might also see something like this:

Choppy Animation from UI

In this case, the UI and render threads are the ones that have work crossing frame boundaries. The UI that we're trying to render on each frame is requiring too much work to be done. In this case, the problem lies in the native views being rendered.

At this point, you'll have some very helpful information to inform your next steps.

JS Issues #

If you identified a JS problem, look for clues in the specific JS that you're executing. In the scenario above, we see RCTEventEmitter being called multiple times per frame. Here's a zoom-in of the JS thread from the trace above:

Too much JS

This doesn't seem right. Why is it being called so often? Are they actually different events? The answers to these questions will probably depend on your product code. And many times, you'll want to look into shouldComponentUpdate.

TODO: Add more tools for profiling JS

Native UI Issues #

If you identified a native UI problem, there are usually two scenarios:

  1. the UI you're trying to draw each frame involves to much work on the GPU, or
  2. You're constructing new UI during the animation/interaction (e.g. loading in new content during a scroll).

Too much GPU work #

In the first scenario, you'll see a trace that has the UI thread and/or Render Thread looking like this:

Overloaded GPU

Notice the long amount of time spent in DrawFrame that crosses frame boundaries. This is time spent waiting for the GPU to drain its command buffer from the previous frame.

To mitigate this, you should:

  • investigate using renderToHardwareTextureAndroid for complex, static content that is being animated/transformed (e.g. the Navigator slide/alpha animations)
  • make sure that you are not using needsOffscreenAlphaCompositing, which is disabled by default, as it greatly increases the per-frame load on the GPU in most cases.

If these don't help and you want to dig deeper into what the GPU is actually doing, you can check out Tracer for OpenGL ES.

Creating new views on the UI thread #

In the second scenario, you'll see something more like this:

Creating Views

Notice that first the JS thread thinks for a bit, then you see some work done on the native modules thread, followed by an expensive traversal on the UI thread.

There isn't an easy way to mitigate this unless you're able to postpone creating new UI until after the interaction, or you are able to simplify the UI you're creating. The react native team is working on a infrastructure level solution for this that will allow new UI to be created and configured off the main thread, allowing the interaction to continue smoothly.

Still stuck? #

If you are confused or stuck, please post ask on Stack Overflow with the react-native tag. If you are unable to get a response there, or find an issue with a core component, please File a Github issue.

← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Colors #

The following formats are supported:

  • '#f0f' (#rgb)
  • '#f0fc' (#rgba)
  • '#ff00ff' (#rrggbb)
  • '#ff00ff00' (#rrggbbaa)
  • 'rgb(255, 255, 255)'
  • 'rgba(255, 255, 255, 1.0)'
  • 'hsl(360, 100%, 100%)'
  • 'hsla(360, 100%, 100%, 1.0)'
  • 'transparent'
  • 'red'
  • 0xff00ff00 (0xrrggbbaa)

For the named colors, React Native follows the CSS3 specification:

  • aliceblue (#f0f8ff)
  • antiquewhite (#faebd7)
  • aqua (#00ffff)
  • aquamarine (#7fffd4)
  • azure (#f0ffff)
  • beige (#f5f5dc)
  • bisque (#ffe4c4)
  • black (#000000)
  • blanchedalmond (#ffebcd)
  • blue (#0000ff)
  • blueviolet (#8a2be2)
  • brown (#a52a2a)
  • burlywood (#deb887)
  • cadetblue (#5f9ea0)
  • chartreuse (#7fff00)
  • chocolate (#d2691e)
  • coral (#ff7f50)
  • cornflowerblue (#6495ed)
  • cornsilk (#fff8dc)
  • crimson (#dc143c)
  • cyan (#00ffff)
  • darkblue (#00008b)
  • darkcyan (#008b8b)
  • darkgoldenrod (#b8860b)
  • darkgray (#a9a9a9)
  • darkgreen (#006400)
  • darkgrey (#a9a9a9)
  • darkkhaki (#bdb76b)
  • darkmagenta (#8b008b)
  • darkolivegreen (#556b2f)
  • darkorange (#ff8c00)
  • darkorchid (#9932cc)
  • darkred (#8b0000)
  • darksalmon (#e9967a)
  • darkseagreen (#8fbc8f)
  • darkslateblue (#483d8b)
  • darkslategray (#2f4f4f)
  • darkslategrey (#2f4f4f)
  • darkturquoise (#00ced1)
  • darkviolet (#9400d3)
  • deeppink (#ff1493)
  • deepskyblue (#00bfff)
  • dimgray (#696969)
  • dimgrey (#696969)
  • dodgerblue (#1e90ff)
  • firebrick (#b22222)
  • floralwhite (#fffaf0)
  • forestgreen (#228b22)
  • fuchsia (#ff00ff)
  • gainsboro (#dcdcdc)
  • ghostwhite (#f8f8ff)
  • gold (#ffd700)
  • goldenrod (#daa520)
  • gray (#808080)
  • green (#008000)
  • greenyellow (#adff2f)
  • grey (#808080)
  • honeydew (#f0fff0)
  • hotpink (#ff69b4)
  • indianred (#cd5c5c)
  • indigo (#4b0082)
  • ivory (#fffff0)
  • khaki (#f0e68c)
  • lavender (#e6e6fa)
  • lavenderblush (#fff0f5)
  • lawngreen (#7cfc00)
  • lemonchiffon (#fffacd)
  • lightblue (#add8e6)
  • lightcoral (#f08080)
  • lightcyan (#e0ffff)
  • lightgoldenrodyellow (#fafad2)
  • lightgray (#d3d3d3)
  • lightgreen (#90ee90)
  • lightgrey (#d3d3d3)
  • lightpink (#ffb6c1)
  • lightsalmon (#ffa07a)
  • lightseagreen (#20b2aa)
  • lightskyblue (#87cefa)
  • lightslategray (#778899)
  • lightslategrey (#778899)
  • lightsteelblue (#b0c4de)
  • lightyellow (#ffffe0)
  • lime (#00ff00)
  • limegreen (#32cd32)
  • linen (#faf0e6)
  • magenta (#ff00ff)
  • maroon (#800000)
  • mediumaquamarine (#66cdaa)
  • mediumblue (#0000cd)
  • mediumorchid (#ba55d3)
  • mediumpurple (#9370db)
  • mediumseagreen (#3cb371)
  • mediumslateblue (#7b68ee)
  • mediumspringgreen (#00fa9a)
  • mediumturquoise (#48d1cc)
  • mediumvioletred (#c71585)
  • midnightblue (#191970)
  • mintcream (#f5fffa)
  • mistyrose (#ffe4e1)
  • moccasin (#ffe4b5)
  • navajowhite (#ffdead)
  • navy (#000080)
  • oldlace (#fdf5e6)
  • olive (#808000)
  • olivedrab (#6b8e23)
  • orange (#ffa500)
  • orangered (#ff4500)
  • orchid (#da70d6)
  • palegoldenrod (#eee8aa)
  • palegreen (#98fb98)
  • paleturquoise (#afeeee)
  • palevioletred (#db7093)
  • papayawhip (#ffefd5)
  • peachpuff (#ffdab9)
  • peru (#cd853f)
  • pink (#ffc0cb)
  • plum (#dda0dd)
  • powderblue (#b0e0e6)
  • purple (#800080)
  • rebeccapurple (#663399)
  • red (#ff0000)
  • rosybrown (#bc8f8f)
  • royalblue (#4169e1)
  • saddlebrown (#8b4513)
  • salmon (#fa8072)
  • sandybrown (#f4a460)
  • seagreen (#2e8b57)
  • seashell (#fff5ee)
  • sienna (#a0522d)
  • silver (#c0c0c0)
  • skyblue (#87ceeb)
  • slateblue (#6a5acd)
  • slategray (#708090)
  • slategrey (#708090)
  • snow (#fffafa)
  • springgreen (#00ff7f)
  • steelblue (#4682b4)
  • tan (#d2b48c)
  • teal (#008080)
  • thistle (#d8bfd8)
  • tomato (#ff6347)
  • turquoise (#40e0d0)
  • violet (#ee82ee)
  • wheat (#f5deb3)
  • white (#ffffff)
  • whitesmoke (#f5f5f5)
  • yellow (#ffff00)
  • yellowgreen (#9acd32)
← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Colors #

The following formats are supported:

  • '#f0f' (#rgb)
  • '#f0fc' (#rgba)
  • '#ff00ff' (#rrggbb)
  • '#ff00ff00' (#rrggbbaa)
  • 'rgb(255, 255, 255)'
  • 'rgba(255, 255, 255, 1.0)'
  • 'hsl(360, 100%, 100%)'
  • 'hsla(360, 100%, 100%, 1.0)'
  • 'transparent'
  • 'red'
  • 0xff00ff00 (0xrrggbbaa)

For the named colors, React Native follows the CSS3 specification:

  • aliceblue (#f0f8ff)
  • antiquewhite (#faebd7)
  • aqua (#00ffff)
  • aquamarine (#7fffd4)
  • azure (#f0ffff)
  • beige (#f5f5dc)
  • bisque (#ffe4c4)
  • black (#000000)
  • blanchedalmond (#ffebcd)
  • blue (#0000ff)
  • blueviolet (#8a2be2)
  • brown (#a52a2a)
  • burlywood (#deb887)
  • cadetblue (#5f9ea0)
  • chartreuse (#7fff00)
  • chocolate (#d2691e)
  • coral (#ff7f50)
  • cornflowerblue (#6495ed)
  • cornsilk (#fff8dc)
  • crimson (#dc143c)
  • cyan (#00ffff)
  • darkblue (#00008b)
  • darkcyan (#008b8b)
  • darkgoldenrod (#b8860b)
  • darkgray (#a9a9a9)
  • darkgreen (#006400)
  • darkgrey (#a9a9a9)
  • darkkhaki (#bdb76b)
  • darkmagenta (#8b008b)
  • darkolivegreen (#556b2f)
  • darkorange (#ff8c00)
  • darkorchid (#9932cc)
  • darkred (#8b0000)
  • darksalmon (#e9967a)
  • darkseagreen (#8fbc8f)
  • darkslateblue (#483d8b)
  • darkslategray (#2f4f4f)
  • darkslategrey (#2f4f4f)
  • darkturquoise (#00ced1)
  • darkviolet (#9400d3)
  • deeppink (#ff1493)
  • deepskyblue (#00bfff)
  • dimgray (#696969)
  • dimgrey (#696969)
  • dodgerblue (#1e90ff)
  • firebrick (#b22222)
  • floralwhite (#fffaf0)
  • forestgreen (#228b22)
  • fuchsia (#ff00ff)
  • gainsboro (#dcdcdc)
  • ghostwhite (#f8f8ff)
  • gold (#ffd700)
  • goldenrod (#daa520)
  • gray (#808080)
  • green (#008000)
  • greenyellow (#adff2f)
  • grey (#808080)
  • honeydew (#f0fff0)
  • hotpink (#ff69b4)
  • indianred (#cd5c5c)
  • indigo (#4b0082)
  • ivory (#fffff0)
  • khaki (#f0e68c)
  • lavender (#e6e6fa)
  • lavenderblush (#fff0f5)
  • lawngreen (#7cfc00)
  • lemonchiffon (#fffacd)
  • lightblue (#add8e6)
  • lightcoral (#f08080)
  • lightcyan (#e0ffff)
  • lightgoldenrodyellow (#fafad2)
  • lightgray (#d3d3d3)
  • lightgreen (#90ee90)
  • lightgrey (#d3d3d3)
  • lightpink (#ffb6c1)
  • lightsalmon (#ffa07a)
  • lightseagreen (#20b2aa)
  • lightskyblue (#87cefa)
  • lightslategray (#778899)
  • lightslategrey (#778899)
  • lightsteelblue (#b0c4de)
  • lightyellow (#ffffe0)
  • lime (#00ff00)
  • limegreen (#32cd32)
  • linen (#faf0e6)
  • magenta (#ff00ff)
  • maroon (#800000)
  • mediumaquamarine (#66cdaa)
  • mediumblue (#0000cd)
  • mediumorchid (#ba55d3)
  • mediumpurple (#9370db)
  • mediumseagreen (#3cb371)
  • mediumslateblue (#7b68ee)
  • mediumspringgreen (#00fa9a)
  • mediumturquoise (#48d1cc)
  • mediumvioletred (#c71585)
  • midnightblue (#191970)
  • mintcream (#f5fffa)
  • mistyrose (#ffe4e1)
  • moccasin (#ffe4b5)
  • navajowhite (#ffdead)
  • navy (#000080)
  • oldlace (#fdf5e6)
  • olive (#808000)
  • olivedrab (#6b8e23)
  • orange (#ffa500)
  • orangered (#ff4500)
  • orchid (#da70d6)
  • palegoldenrod (#eee8aa)
  • palegreen (#98fb98)
  • paleturquoise (#afeeee)
  • palevioletred (#db7093)
  • papayawhip (#ffefd5)
  • peachpuff (#ffdab9)
  • peru (#cd853f)
  • pink (#ffc0cb)
  • plum (#dda0dd)
  • powderblue (#b0e0e6)
  • purple (#800080)
  • rebeccapurple (#663399)
  • red (#ff0000)
  • rosybrown (#bc8f8f)
  • royalblue (#4169e1)
  • saddlebrown (#8b4513)
  • salmon (#fa8072)
  • sandybrown (#f4a460)
  • seagreen (#2e8b57)
  • seashell (#fff5ee)
  • sienna (#a0522d)
  • silver (#c0c0c0)
  • skyblue (#87ceeb)
  • slateblue (#6a5acd)
  • slategray (#708090)
  • slategrey (#708090)
  • snow (#fffafa)
  • springgreen (#00ff7f)
  • steelblue (#4682b4)
  • tan (#d2b48c)
  • teal (#008080)
  • thistle (#d8bfd8)
  • tomato (#ff6347)
  • turquoise (#40e0d0)
  • violet (#ee82ee)
  • wheat (#f5deb3)
  • white (#ffffff)
  • whitesmoke (#f5f5f5)
  • yellow (#ffff00)
  • yellowgreen (#9acd32)
← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Gesture Responder System #

Gesture recognition on mobile devices is much more complicated than web. A touch can go through several phases as the app determines what the user's intention is. For example, the app needs to determine if the touch is scrolling, sliding on a widget, or tapping. This can even change during the duration of a touch. There can also be multiple simultaneous touches.

The touch responder system is needed to allow components to negotiate these touch interactions without any additional knowledge about their parent or child components. This system is implemented in ResponderEventPlugin.js, which contains further details and documentation.

Best Practices #

Users can feel huge differences in the usability of web apps vs. native, and this is one of the big causes. Every action should have the following attributes:

  • Feedback/highlighting- show the user what is handling their touch, and what will happen when they release the gesture
  • Cancel-ability- when making an action, the user should be able to abort it mid-touch by dragging their finger away

These features make users more comfortable while using an app, because it allows people to experiment and interact without fear of making mistakes.

TouchableHighlight and Touchable* #

The responder system can be complicated to use. So we have provided an abstract Touchable implementation for things that should be "tappable". This uses the responder system and allows you to easily configure tap interactions declaratively. Use TouchableHighlight anywhere where you would use a button or link on web.

Responder Lifecycle #

A view can become the touch responder by implementing the correct negotiation methods. There are two methods to ask the view if it wants to become responder:

  • View.props.onStartShouldSetResponder: (evt) => true, - Does this view want to become responder on the start of a touch?
  • View.props.onMoveShouldSetResponder: (evt) => true, - Called for every touch move on the View when it is not the responder: does this view want to "claim" touch responsiveness?

If the View returns true and attempts to become the responder, one of the following will happen:

  • View.props.onResponderGrant: (evt) => {} - The View is now responding for touch events. This is the time to highlight and show the user what is happening
  • View.props.onResponderReject: (evt) => {} - Something else is the responder right now and will not release it

If the view is responding, the following handlers can be called:

  • View.props.onResponderMove: (evt) => {} - The user is moving their finger
  • View.props.onResponderRelease: (evt) => {} - Fired at the end of the touch, ie "touchUp"
  • View.props.onResponderTerminationRequest: (evt) => true - Something else wants to become responder. Should this view release the responder? Returning true allows release
  • View.props.onResponderTerminate: (evt) => {} - The responder has been taken from the View. Might be taken by other views after a call to onResponderTerminationRequest, or might be taken by the OS without asking (happens with control center/ notification center on iOS)

evt is a synthetic touch event with the following form:

  • nativeEvent
    • changedTouches - Array of all touch events that have changed since the last event
    • identifier - The ID of the touch
    • locationX - The X position of the touch, relative to the element
    • locationY - The Y position of the touch, relative to the element
    • pageX - The X position of the touch, relative to the root element
    • pageY - The Y position of the touch, relative to the root element
    • target - The node id of the element receiving the touch event
    • timeStamp - A time identifier for the touch, useful for velocity calculation
    • touches - Array of all current touches on the screen

Capture ShouldSet Handlers #

onStartShouldSetResponder and onMoveShouldSetResponder are called with a bubbling pattern, where the deepest node is called first. That means that the deepest component will become responder when multiple Views return true for *ShouldSetResponder handlers. This is desirable in most cases, because it makes sure all controls and buttons are usable.

However, sometimes a parent will want to make sure that it becomes responder. This can be handled by using the capture phase. Before the responder system bubbles up from the deepest component, it will do a capture phase, firing on*ShouldSetResponderCapture. So if a parent View wants to prevent the child from becoming responder on a touch start, it should have a onStartShouldSetResponderCapture handler which returns true.

  • View.props.onStartShouldSetResponderCapture: (evt) => true,
  • View.props.onMoveShouldSetResponderCapture: (evt) => true,

PanResponder #

For higher-level gesture interpretation, check out PanResponder.

← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Gesture Responder System #

Gesture recognition on mobile devices is much more complicated than web. A touch can go through several phases as the app determines what the user's intention is. For example, the app needs to determine if the touch is scrolling, sliding on a widget, or tapping. This can even change during the duration of a touch. There can also be multiple simultaneous touches.

The touch responder system is needed to allow components to negotiate these touch interactions without any additional knowledge about their parent or child components. This system is implemented in ResponderEventPlugin.js, which contains further details and documentation.

Best Practices #

Users can feel huge differences in the usability of web apps vs. native, and this is one of the big causes. Every action should have the following attributes:

  • Feedback/highlighting- show the user what is handling their touch, and what will happen when they release the gesture
  • Cancel-ability- when making an action, the user should be able to abort it mid-touch by dragging their finger away

These features make users more comfortable while using an app, because it allows people to experiment and interact without fear of making mistakes.

TouchableHighlight and Touchable* #

The responder system can be complicated to use. So we have provided an abstract Touchable implementation for things that should be "tappable". This uses the responder system and allows you to easily configure tap interactions declaratively. Use TouchableHighlight anywhere where you would use a button or link on web.

Responder Lifecycle #

A view can become the touch responder by implementing the correct negotiation methods. There are two methods to ask the view if it wants to become responder:

  • View.props.onStartShouldSetResponder: (evt) => true, - Does this view want to become responder on the start of a touch?
  • View.props.onMoveShouldSetResponder: (evt) => true, - Called for every touch move on the View when it is not the responder: does this view want to "claim" touch responsiveness?

If the View returns true and attempts to become the responder, one of the following will happen:

  • View.props.onResponderGrant: (evt) => {} - The View is now responding for touch events. This is the time to highlight and show the user what is happening
  • View.props.onResponderReject: (evt) => {} - Something else is the responder right now and will not release it

If the view is responding, the following handlers can be called:

  • View.props.onResponderMove: (evt) => {} - The user is moving their finger
  • View.props.onResponderRelease: (evt) => {} - Fired at the end of the touch, ie "touchUp"
  • View.props.onResponderTerminationRequest: (evt) => true - Something else wants to become responder. Should this view release the responder? Returning true allows release
  • View.props.onResponderTerminate: (evt) => {} - The responder has been taken from the View. Might be taken by other views after a call to onResponderTerminationRequest, or might be taken by the OS without asking (happens with control center/ notification center on iOS)

evt is a synthetic touch event with the following form:

  • nativeEvent
    • changedTouches - Array of all touch events that have changed since the last event
    • identifier - The ID of the touch
    • locationX - The X position of the touch, relative to the element
    • locationY - The Y position of the touch, relative to the element
    • pageX - The X position of the touch, relative to the root element
    • pageY - The Y position of the touch, relative to the root element
    • target - The node id of the element receiving the touch event
    • timeStamp - A time identifier for the touch, useful for velocity calculation
    • touches - Array of all current touches on the screen

Capture ShouldSet Handlers #

onStartShouldSetResponder and onMoveShouldSetResponder are called with a bubbling pattern, where the deepest node is called first. That means that the deepest component will become responder when multiple Views return true for *ShouldSetResponder handlers. This is desirable in most cases, because it makes sure all controls and buttons are usable.

However, sometimes a parent will want to make sure that it becomes responder. This can be handled by using the capture phase. Before the responder system bubbles up from the deepest component, it will do a capture phase, firing on*ShouldSetResponderCapture. So if a parent View wants to prevent the child from becoming responder on a touch start, it should have a onStartShouldSetResponderCapture handler which returns true.

  • View.props.onStartShouldSetResponderCapture: (evt) => true,
  • View.props.onMoveShouldSetResponderCapture: (evt) => true,

PanResponder #

For higher-level gesture interpretation, check out PanResponder.

← PrevNext →

You can edit the content above on GitHub and send us a pull request!

-
Next →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

ImagePickerIOS #

Methods #

static canRecordVideos(callback) #

static canUseCamera(callback) #

static openCameraDialog(config, successCallback, cancelCallback) #

static openSelectDialog(config, successCallback, cancelCallback) #

You can edit the content above on GitHub and send us a pull request!

← PrevNext →
React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

ImagePickerIOS #

Methods #

static canRecordVideos(callback) #

static canUseCamera(callback) #

static openCameraDialog(config, successCallback, cancelCallback) #

static openSelectDialog(config, successCallback, cancelCallback) #

You can edit the content above on GitHub and send us a pull request!

← PrevNext →
-

Creating a release build in Android Studio #

You can use Android Studio to create your release builds too! It’s as easy as creating release builds of your previously-existing native Android app. There’s just one additional step, which you’ll have to do before every release build. You need to execute the following to create a React Native bundle, which’ll be included with your native Android app:

$ react-native bundle --platform android --dev false --entry-file index.android.js --bundle-output android/com/your-company-name/app-package-name/src/main/assets/index.android.bundle --assets-dest android/com/your-company-name/app-package-name/src/main/res/

Don’t forget to replace the paths with correct ones and create the assets folder if it doesn’t exist!

Now just create a release build of your native app from within Android Studio as usual and you should be good to go!

← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

JavaScript Environment #

JavaScript Runtime #

When using React Native, you're going to be running your JavaScript code in two environments:

  • On iOS simulators and devices, Android emulators and devices React Native uses JavaScriptCore which is the JavaScript engine that powers Safari. On iOS JSC doesn't use JIT due to the absence of writable executable memory in iOS apps.
  • When using Chrome debugging, it runs all the JavaScript code within Chrome itself and communicates with native code via WebSocket. So you are using V8.

While both environments are very similar, you may end up hitting some inconsistencies. We're likely going to experiment with other JS engines in the future, so it's best to avoid relying on specifics of any runtime.

JavaScript Syntax Transformers #

Syntax transformers make writing code more enjoyable by allowing you to use new JavaScript syntax without having to wait for support on all interpreters.

As of version 0.5.0, React Native ships with the Babel JavaScript compiler. Check Babel documentation on its supported transformations for more details.

Here's a full list of React Native's enabled transformations.

ES5

  • Reserved Words: promise.catch(function() { });

ES6

ES7

Specific

  • JSX: <View style={{color: 'red'}} />
  • Flow: function foo(x: ?number): string {}

Polyfills #

Many standards functions are also available on all the supported JavaScript runtimes.

Browser

ES6

ES7

Specific

  • __DEV__
← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

JavaScript Environment #

JavaScript Runtime #

When using React Native, you're going to be running your JavaScript code in two environments:

  • On iOS simulators and devices, Android emulators and devices React Native uses JavaScriptCore which is the JavaScript engine that powers Safari. On iOS JSC doesn't use JIT due to the absence of writable executable memory in iOS apps.
  • When using Chrome debugging, it runs all the JavaScript code within Chrome itself and communicates with native code via WebSocket. So you are using V8.

While both environments are very similar, you may end up hitting some inconsistencies. We're likely going to experiment with other JS engines in the future, so it's best to avoid relying on specifics of any runtime.

JavaScript Syntax Transformers #

Syntax transformers make writing code more enjoyable by allowing you to use new JavaScript syntax without having to wait for support on all interpreters.

As of version 0.5.0, React Native ships with the Babel JavaScript compiler. Check Babel documentation on its supported transformations for more details.

Here's a full list of React Native's enabled transformations.

ES5

  • Reserved Words: promise.catch(function() { });

ES6

ES7

Specific

  • JSX: <View style={{color: 'red'}} />
  • Flow: function foo(x: ?number): string {}

Polyfills #

Many standards functions are also available on all the supported JavaScript runtimes.

Browser

ES6

ES7

Specific

  • __DEV__
← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

More Resources #

If you just read through this website, you should be able to build a pretty cool React Native app. But React Native isn't just a product made by one company - it's a community of thousands of developers. So if you're interested in React Native, here's some related stuff you might want to check out.

Popular Libraries #

If you're using React Native, you probably already know about React. So I feel a bit silly mentioning this. But if you haven't, check out React - it's the best way to build a modern website.

One common question is how to handle the "state" of your React Native application. The most popular library for this is Redux. Don't be afraid of how often Redux uses the word "reducer" - it's a pretty simple library, and there's also a nice series of videos explaining it.

If you're looking for a library that does a specific thing, check out Awesome React Native, a curated list of components that also has demos, articles, and other stuff.

Example Apps #

There are a lot of example apps at the React Native Playground. You can see the code running on a real device, which is a neat feature.

The folks who built the app for Facebook's F8 conference in 2016 also open-sourced the code and wrote up a detailed series of tutorials. This is useful if you want a more in-depth example that's more realistic than most sample apps out there.

Development Tools #

Nuclide is the IDE that Facebook uses internally for React Native development. The killer feature of Nuclide is its debugging ability. It also has great inline Flow support.

Ignite is a starter kit that uses Redux and a few different common UI libraries. It has a CLI to generate apps, components, and containers. If you like all of the individual tech choices, Ignite could be perfect for you.

CodePush is a service from Microsoft that makes it easy to deploy live updates to your React Native app. If you don't like going through the app store process to deploy little tweaks, and you also don't like setting up your own backend, give CodePush a try.

Exponent is a development environment plus application that focuses on letting you build React Native apps in the Exponent development environment, without ever touching Xcode or Android Studio. If you wish React Native was even more JavaScripty and webby, check out Exponent.

Deco is an all-in-one development environment specifically designed for React Native. It can automatically set up a new project, search for open source components, and insert them. You can also tweak your app graphically in real time. Check it out if you use macOS.

Where React Native People Hang Out #

The React Native Community Facebook group has thousands of developers, and it's pretty active. Come there to show off your project, or ask how other people solved similar problems.

Reactiflux is a Discord chat where a lot of React-related discussion happens, including React Native. Discord is just like Slack except it works better for open source projects with a zillion contributors. Check out the #react-native channel.

The React Twitter account covers both React and React Native. Follow the React Native Twitter account and blog to find out what's happening in the world of React Native.

There are a lot of React Native Meetups that happen around the world. Often there is React Native content in React meetups as well.

Sometimes we have React conferences. We posted the videos from React.js Conf 2016, and we'll probably have more conferences in the future, too. Stay tuned.

← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

More Resources #

If you just read through this website, you should be able to build a pretty cool React Native app. But React Native isn't just a product made by one company - it's a community of thousands of developers. So if you're interested in React Native, here's some related stuff you might want to check out.

Popular Libraries #

If you're using React Native, you probably already know about React. So I feel a bit silly mentioning this. But if you haven't, check out React - it's the best way to build a modern website.

One common question is how to handle the "state" of your React Native application. The most popular library for this is Redux. Don't be afraid of how often Redux uses the word "reducer" - it's a pretty simple library, and there's also a nice series of videos explaining it.

If you're looking for a library that does a specific thing, check out Awesome React Native, a curated list of components that also has demos, articles, and other stuff.

Example Apps #

There are a lot of example apps at the React Native Playground. You can see the code running on a real device, which is a neat feature.

The folks who built the app for Facebook's F8 conference in 2016 also open-sourced the code and wrote up a detailed series of tutorials. This is useful if you want a more in-depth example that's more realistic than most sample apps out there.

Development Tools #

Nuclide is the IDE that Facebook uses internally for React Native development. The killer feature of Nuclide is its debugging ability. It also has great inline Flow support.

Ignite is a starter kit that uses Redux and a few different common UI libraries. It has a CLI to generate apps, components, and containers. If you like all of the individual tech choices, Ignite could be perfect for you.

CodePush is a service from Microsoft that makes it easy to deploy live updates to your React Native app. If you don't like going through the app store process to deploy little tweaks, and you also don't like setting up your own backend, give CodePush a try.

Exponent is a development environment plus application that focuses on letting you build React Native apps in the Exponent development environment, without ever touching Xcode or Android Studio. If you wish React Native was even more JavaScripty and webby, check out Exponent.

Deco is an all-in-one development environment specifically designed for React Native. It can automatically set up a new project, search for open source components, and insert them. You can also tweak your app graphically in real time. Check it out if you use macOS.

Where React Native People Hang Out #

The React Native Community Facebook group has thousands of developers, and it's pretty active. Come there to show off your project, or ask how other people solved similar problems.

Reactiflux is a Discord chat where a lot of React-related discussion happens, including React Native. Discord is just like Slack except it works better for open source projects with a zillion contributors. Check out the #react-native channel.

The React Twitter account covers both React and React Native. Follow the React Native Twitter account and blog to find out what's happening in the world of React Native.

There are a lot of React Native Meetups that happen around the world. Often there is React Native content in React meetups as well.

Sometimes we have React conferences. We posted the videos from React.js Conf 2016, and we'll probably have more conferences in the future, too. Stay tuned.

← PrevNext →

You can edit the content above on GitHub and send us a pull request!

-
← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Running On Simulator #

Starting the simulator #

Once you have your React Native project initialized, you can run react-native run-ios inside the newly created project directory. If everything is set up correctly, you should see your new app running in the iOS Simulator shortly.

Specifying a device #

You can specify the device the simulator should run with the --simulator flag, followed by the device name as a string. The default is "iPhone 6". If you wish to run your app on an iPhone 4s, just run react-native run-ios --simulator "iPhone 4s".

The device names correspond to the list of devices available in Xcode. You can check your available devices by running xcrun simctl list devices from the console.

← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Running On Simulator #

Starting the simulator #

Once you have your React Native project initialized, you can run react-native run-ios inside the newly created project directory. If everything is set up correctly, you should see your new app running in the iOS Simulator shortly.

Specifying a device #

You can specify the device the simulator should run with the --simulator flag, followed by the device name as a string. The default is "iPhone 6". If you wish to run your app on an iPhone 4s, just run react-native run-ios --simulator "iPhone 4s".

The device names correspond to the list of devices available in Xcode. You can check your available devices by running xcrun simctl list devices from the console.

← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Settings #

Methods #

static get(key) #

static set(settings) #

static watchKeys(keys, callback) #

static clearWatch(watchId) #

Properties #

You can edit the content above on GitHub and send us a pull request!

← PrevNext →
React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Settings #

Methods #

static get(key) #

static set(settings) #

static watchKeys(keys, callback) #

static clearWatch(watchId) #

Properties #

You can edit the content above on GitHub and send us a pull request!

← PrevNext →
React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Shadow Props #

Props #

iosshadowColor color #

Sets the drop shadow color

iosshadowOffset {width: number, height: number} #

Sets the drop shadow offset

iosshadowOpacity number #

Sets the drop shadow opacity (multiplied by the color's alpha component)

iosshadowRadius number #

Sets the drop shadow blur radius

You can edit the content above on GitHub and send us a pull request!

← Prev
React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Shadow Props #

Props #

iosshadowColor color #

Sets the drop shadow color

iosshadowOffset {width: number, height: number} #

Sets the drop shadow offset

iosshadowOpacity number #

Sets the drop shadow opacity (multiplied by the color's alpha component)

iosshadowRadius number #

Sets the drop shadow blur radius

You can edit the content above on GitHub and send us a pull request!

← Prev
React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

SnapshotViewIOS #

Props #

View props... #

onSnapshotReady function #

testIdentifier string #

You can edit the content above on GitHub and send us a pull request!

← PrevNext →
React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

SnapshotViewIOS #

Props #

View props... #

onSnapshotReady function #

testIdentifier string #

You can edit the content above on GitHub and send us a pull request!

← PrevNext →
React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

StatusBarIOS #

Use StatusBar for mutating the status bar.

You can edit the content above on GitHub and send us a pull request!

← PrevNext →
React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

StatusBarIOS #

Use StatusBar for mutating the status bar.

You can edit the content above on GitHub and send us a pull request!

← PrevNext →
React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Testing #

Running Tests and Contributing #

The React Native repo has several tests you can run to verify you haven't caused a regression with your PR. These tests are run with the Travis and CircleCI continuous integration systems, and will automatically post the results to your PR.

We don't have perfect test coverage of course, especially for complex end-to-end interactions with the user, so many changes will still require significant manual verification, but we would love it if you want to help us increase our test coverage and add more tests and test cases!

Jest Tests #

Jest tests are JS-only tests run on the command line with node. The tests themselves live in the __tests__ directories of the files they test, and there is a large emphasis on aggressively mocking out functionality that is not under test for failure isolation and maximum speed. You can run the existing React Native jest tests with

npm test

from the react-native root, and we encourage you to add your own tests for any components you want to contribute to. See getImageSource-test.js for a basic example.

To use Jest for your react-native projects we recommend following the React-Native Tutorial on the Jest website.

Unit tests (Android) #

React Native uses the Buck build tool to run tests. Unit tests run locally on your machine, no emulator is needed. To run the tests:

$ cd react-native $ ./scripts/run-android-local-unit-tests.sh

Integration tests (Android) #

React Native uses the Buck build tool to run tests. Integration tests run on an emulator / device and verify that modules and components, as well as the core parts of React Native (such as the bridge) work well end-to-end.

Make sure you have the path to the Android NDK set up, see Prerequisites.

To run the tests:

$ cd react-native $ npm install -$ ./scripts/run-android-local-integration-tests.sh

Integration Tests (iOS) #

React Native provides facilities to make it easier to test integrated components that require both native and JS components to communicate across the bridge. The two main components are RCTTestRunner and RCTTestModule. RCTTestRunner sets up the ReactNative environment and provides facilities to run the tests as XCTestCases in Xcode (runTest:module is the simplest method). RCTTestModule is exported to JS as NativeModules.TestModule. The tests themselves are written in JS, and must call TestModule.markTestCompleted() when they are done, otherwise the test will timeout and fail. Test failures are primarily indicated by throwing a JS exception. It is also possible to test error conditions with runTest:module:initialProps:expectErrorRegex: or runTest:module:initialProps:expectErrorBlock: which will expect an error to be thrown and verify the error matches the provided criteria. See IntegrationTestHarnessTest.js, UIExplorerIntegrationTests.m, and IntegrationTestsApp.js for example usage and integration points.

You can run integration tests locally with cmd+U in the IntegrationTest and UIExplorer apps in Xcode.

Screenshot/Snapshot Tests (iOS) #

A common type of integration test is the snapshot test. These tests render a component, and verify snapshots of the screen against reference images using TestModule.verifySnapshot(), using the FBSnapshotTestCase library behind the scenes. Reference images are recorded by setting recordMode = YES on the RCTTestRunner, then running the tests. Snapshots will differ slightly between 32 and 64 bit, and various OS versions, so it's recommended that you enforce tests are run with the correct configuration. It's also highly recommended that all network data be mocked out, along with other potentially troublesome dependencies. See SimpleSnapshotTest for a basic example.

If you make a change that affects a snapshot test in a PR, such as adding a new example case to one of the examples that is snapshotted, you'll need to re-record the snapshot reference image. To do this, simply change to _runner.recordMode = YES; in UIExplorer/UIExplorerSnapshotTests.m, re-run the failing tests, then flip record back to NO and submit/update your PR and wait to see if the Travis build passes.

← PrevNext →

You can edit the content above on GitHub and send us a pull request!

React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Transforms #

Props #

decomposedMatrix DecomposedMatrixPropType #

transform [{perspective: number}, {rotate: string}, {rotateX: string}, {rotateY: string}, {rotateZ: string}, {scale: number}, {scaleX: number}, {scaleY: number}, {translateX: number}, {translateY: number}, {skewX: string}, {skewY: string}] #

transformMatrix TransformMatrixPropType #

You can edit the content above on GitHub and send us a pull request!

← PrevNext →
React Nativenext

The Basics

Guides

Guides (iOS)

Guides (Android)

components

apis

Transforms #

Props #

decomposedMatrix DecomposedMatrixPropType #

transform [{perspective: number}, {rotate: string}, {rotateX: string}, {rotateY: string}, {rotateZ: string}, {scale: number}, {scaleX: number}, {scaleY: number}, {translateX: number}, {translateY: number}, {skewX: string}, {skewY: string}] #

transformMatrix TransformMatrixPropType #

You can edit the content above on GitHub and send us a pull request!

← PrevNext →
React Nativenext

React Native Versions

React Native follows a 2-week release train. Every two weeks, a new branch created off master enters the Release Candidate phase, and the previous Release Candidate branch is released and considered stable.

Current Version (Stable)

0.37DocumentationRelease Notes

This is the version that is configured automatically when you run react-native init. We highly recommend using the current version of React Native when starting a new project.

If you have an existing project that uses React Native, read the release notes to learn about new features and fixes. You can follow our guide to upgrade your app to the latest version.

Pre-release Versions

masterDocumentation
0.38-RCDocumentationRelease Notes

For those who live on the bleeding edge. Only recommended if you're actively contributing code to React Native, or if you need to verify how your application behaves in an upcoming release.

Past Versions

0.36DocumentationRelease Notes
0.35DocumentationRelease Notes
0.34DocumentationRelease Notes
0.33DocumentationRelease Notes
0.32DocumentationRelease Notes
0.31DocumentationRelease Notes
0.30DocumentationRelease Notes
0.29DocumentationRelease Notes
0.28DocumentationRelease Notes
0.27DocumentationRelease Notes
0.26DocumentationRelease Notes
0.25DocumentationRelease Notes
0.24DocumentationRelease Notes
0.23DocumentationRelease Notes
0.22DocumentationRelease Notes
0.21DocumentationRelease Notes
0.20DocumentationRelease Notes
0.19DocumentationRelease Notes
0.18DocumentationRelease Notes

You can find past versions of React Native on GitHub. The release notes can be useful if you would like to learn when a specific feature or fix was released.

You can also view the docs for a particular version of React Native by clicking on the Docs link next to the release in this page. You can come back to this page and switch the version of the docs you're reading at any time by clicking on the version number at the top of the page.

React Nativenext

React Native Versions

React Native follows a 2-week release train. Every two weeks, a new branch created off master enters the Release Candidate phase, and the previous Release Candidate branch is released and considered stable.

Current Version (Stable)

0.37DocumentationRelease Notes

This is the version that is configured automatically when you run react-native init. We highly recommend using the current version of React Native when starting a new project.

If you have an existing project that uses React Native, read the release notes to learn about new features and fixes. You can follow our guide to upgrade your app to the latest version.

Pre-release Versions

masterDocumentation
0.38-RCDocumentationRelease Notes

For those who live on the bleeding edge. Only recommended if you're actively contributing code to React Native, or if you need to verify how your application behaves in an upcoming release.

Past Versions

0.36DocumentationRelease Notes
0.35DocumentationRelease Notes
0.34DocumentationRelease Notes
0.33DocumentationRelease Notes
0.32DocumentationRelease Notes
0.31DocumentationRelease Notes
0.30DocumentationRelease Notes
0.29DocumentationRelease Notes
0.28DocumentationRelease Notes
0.27DocumentationRelease Notes
0.26DocumentationRelease Notes
0.25DocumentationRelease Notes
0.24DocumentationRelease Notes
0.23DocumentationRelease Notes
0.22DocumentationRelease Notes
0.21DocumentationRelease Notes
0.20DocumentationRelease Notes
0.19DocumentationRelease Notes
0.18DocumentationRelease Notes

You can find past versions of React Native on GitHub. The release notes can be useful if you would like to learn when a specific feature or fix was released.

You can also view the docs for a particular version of React Native by clicking on the Docs link next to the release in this page. You can come back to this page and switch the version of the docs you're reading at any time by clicking on the version number at the top of the page.

React Nativenext

Who's using React Native?

Thousands of apps are using React Native, from established Fortune 500 companies to hot new startups. If you're curious to see what can be accomplished with React Native, check out these apps!

Instagram

Instagram

iOS · Android

Vogue

Vogue

iOS

Start - medication manager for depression

Start - medication manager for depression

iOS

NYT: A Health Startup Turns to Consumers

Taxfyle - taxes filed on-demand via licensed CPA

Taxfyle - taxes filed on-demand via licensed CPA

iOS

Taxfyle: the Uber for filing taxes

Some of these are hybrid native/React Native apps. If you built a popular application using React Native, we'd love to have your app on this showcase. Check out the guidelines on GitHub to update this page.

Also, a curated list of open source React Native apps is being kept by React Native News.

React Nativenext

Who's using React Native?

Thousands of apps are using React Native, from established Fortune 500 companies to hot new startups. If you're curious to see what can be accomplished with React Native, check out these apps!

Instagram

Instagram

iOS · Android

Vogue

Vogue

iOS

Start - medication manager for depression

Start - medication manager for depression

iOS

NYT: A Health Startup Turns to Consumers

Taxfyle - taxes filed on-demand via licensed CPA

Taxfyle - taxes filed on-demand via licensed CPA

iOS

Taxfyle: the Uber for filing taxes

Some of these are hybrid native/React Native apps. If you built a popular application using React Native, we'd love to have your app on this showcase. Check out the guidelines on GitHub to update this page.

Also, a curated list of open source React Native apps is being kept by React Native News.

React Nativenext

Need help?

At Facebook, there are dozens of engineers who work on React Native full-time. But there are far more people in the community who make key contributions and fix things. So if you need help with your React Native app, the right place to go depends on the type of help that you need.

Browse the docs

Find what you're looking for in our detailed documentation and guides.

Explore samples

Take apart these fully built applications, and get some inspiration for your own.

Stay up to date

Find out what's happening in the world of React Native.

Join the community

Connect with other React Native developers. Show off your project, or ask how other people solved similar problems.

  • Frequently Asked Questions

    Many React Native users are active on Stack Overflow. Browse existing questions, or ask your own technical question.

  • React Native Community

    If you have an open-ended question or you just want to get a general sense of what React Native folks talk about, check out the React Native Community Facebook group. It has thousands of developers and almost all posts get a response.

  • Reactiflux Chat

    If you need an answer right away, check out the #react-native channel. There are usually a number of React Native experts there who can help out or point you to somewhere you might want to look.

Contribute

React Native is open source! Issues and pull requests are welcome.

  • Get Involved

    If you want to contribute, take a look at the list of good first tasks on GitHub.

  • Feature Requests

    If you have a feature request, add it to the list or upvote a similar one. The voting system helps surface which issues are most important to the community.

  • Report a Bug

    If you have discovered a bug in React Native, consider submitting a pull request with a fix. If you don't think you can fix it yourself, you can open an issue on GitHub.

React Nativenext

Need help?

At Facebook, there are dozens of engineers who work on React Native full-time. But there are far more people in the community who make key contributions and fix things. So if you need help with your React Native app, the right place to go depends on the type of help that you need.

Browse the docs

Find what you're looking for in our detailed documentation and guides.

Explore samples

Take apart these fully built applications, and get some inspiration for your own.

Stay up to date

Find out what's happening in the world of React Native.

Join the community

Connect with other React Native developers. Show off your project, or ask how other people solved similar problems.

  • Frequently Asked Questions

    Many React Native users are active on Stack Overflow. Browse existing questions, or ask your own technical question.

  • React Native Community

    If you have an open-ended question or you just want to get a general sense of what React Native folks talk about, check out the React Native Community Facebook group. It has thousands of developers and almost all posts get a response.

  • Reactiflux Chat

    If you need an answer right away, check out the #react-native channel. There are usually a number of React Native experts there who can help out or point you to somewhere you might want to look.

Contribute

React Native is open source! Issues and pull requests are welcome.

  • Get Involved

    If you want to contribute, take a look at the list of good first tasks on GitHub.

  • Feature Requests

    If you have a feature request, add it to the list or upvote a similar one. The voting system helps surface which issues are most important to the community.

  • Report a Bug

    If you have discovered a bug in React Native, consider submitting a pull request with a fix. If you don't think you can fix it yourself, you can open an issue on GitHub.

React Nativenext

React Native Versions

React Native follows a 2-week release train. Every two weeks, a new branch created off master enters the Release Candidate phase, and the previous Release Candidate branch is released and considered stable.

Current Version (Stable)

0.37DocumentationRelease Notes

This is the version that is configured automatically when you run react-native init. We highly recommend using the current version of React Native when starting a new project.

If you have an existing project that uses React Native, read the release notes to learn about new features and fixes. You can follow our guide to upgrade your app to the latest version.

Pre-release Versions

masterDocumentation
0.38-RCDocumentationRelease Notes

For those who live on the bleeding edge. Only recommended if you're actively contributing code to React Native, or if you need to verify how your application behaves in an upcoming release.

Past Versions

0.36DocumentationRelease Notes
0.35DocumentationRelease Notes
0.34DocumentationRelease Notes
0.33DocumentationRelease Notes
0.32DocumentationRelease Notes
0.31DocumentationRelease Notes
0.30DocumentationRelease Notes
0.29DocumentationRelease Notes
0.28DocumentationRelease Notes
0.27DocumentationRelease Notes
0.26DocumentationRelease Notes
0.25DocumentationRelease Notes
0.24DocumentationRelease Notes
0.23DocumentationRelease Notes
0.22DocumentationRelease Notes
0.21DocumentationRelease Notes
0.20DocumentationRelease Notes
0.19DocumentationRelease Notes
0.18DocumentationRelease Notes

You can find past versions of React Native on GitHub. The release notes can be useful if you would like to learn when a specific feature or fix was released.

You can also view the docs for a particular version of React Native by clicking on the Docs link next to the release in this page. You can come back to this page and switch the version of the docs you're reading at any time by clicking on the version number at the top of the page.

React Nativenext

React Native Versions

React Native follows a 2-week release train. Every two weeks, a new branch created off master enters the Release Candidate phase, and the previous Release Candidate branch is released and considered stable.

Current Version (Stable)

0.37DocumentationRelease Notes

This is the version that is configured automatically when you run react-native init. We highly recommend using the current version of React Native when starting a new project.

If you have an existing project that uses React Native, read the release notes to learn about new features and fixes. You can follow our guide to upgrade your app to the latest version.

Pre-release Versions

masterDocumentation
0.38-RCDocumentationRelease Notes

For those who live on the bleeding edge. Only recommended if you're actively contributing code to React Native, or if you need to verify how your application behaves in an upcoming release.

Past Versions

0.36DocumentationRelease Notes
0.35DocumentationRelease Notes
0.34DocumentationRelease Notes
0.33DocumentationRelease Notes
0.32DocumentationRelease Notes
0.31DocumentationRelease Notes
0.30DocumentationRelease Notes
0.29DocumentationRelease Notes
0.28DocumentationRelease Notes
0.27DocumentationRelease Notes
0.26DocumentationRelease Notes
0.25DocumentationRelease Notes
0.24DocumentationRelease Notes
0.23DocumentationRelease Notes
0.22DocumentationRelease Notes
0.21DocumentationRelease Notes
0.20DocumentationRelease Notes
0.19DocumentationRelease Notes
0.18DocumentationRelease Notes

You can find past versions of React Native on GitHub. The release notes can be useful if you would like to learn when a specific feature or fix was released.

You can also view the docs for a particular version of React Native by clicking on the Docs link next to the release in this page. You can come back to this page and switch the version of the docs you're reading at any time by clicking on the version number at the top of the page.