Joshua GrossandFacebook GitHub Bot
c6b9cc36da
Summary: In https://github.com/facebook/react-native/commit/0b63c9464872fed9ff3eb388e32850f2f8c69561, I shipped "Early ViewCommand Dispatch" everywhere but didn't provide a good summary in the commit message. Here it is: The "Early ViewCommand Dispatch" experiment was a success, leading to improved UI responsiveness and fewer overall crashes. Ship to all Fabric and non-Fabric users, and clean up the code a bit. # Context: what? ViewCommands are now used in React Native to do things like scroll ScrollViews to a certain position; focus or blur a TextInput; control the value of controlled TextInputs; and much more. These used to be done using setNativeProps, but we're moving everything to ViewCommands, and most of that migration has already finished. # Context: Why? Because Fabric does not support setNativeProps, there has been an effort to move all setNativeProps callsites to ViewCommands. Since these callsites are in JS where we can't tell if we're running in Paper or Fabric, both Paper and Fabric callsites are being migrated (mostly already done) to ViewCommands. One such example is Android TextInput, which has been using ViewCommands instead of setNativeProps for several months. This migration was largely without issues, except TheSavior and I noticed early on that certain things were just... slower with ViewCommands. It was definitely noticeable, but we determined it to be acceptable and moved on. Recently, it became clear to me that the perf regression may not be acceptable, but there might be an "easy" solution. # Why are ViewCommands slower than SetNativeProps? So, a couple things. SetNativeProps on Paper would actually cause a layout pass; the same is not true for ViewCommands, so they should actually be much faster. But they're not! The reason is that ViewCommands are treated as regular mount items, and they are queued up /after/ all other mount items. That means if you're trying to interact with the UI while some part of it is updating, your ViewCommands must wait for portions of the screen to finish rendering before they execute. In some cases, those views may even disappear before the ViewCommand executes, causing increased exceptions as well as speed degredations. # Proposal This experiment that ran with successful results was: to execute ViewCommands /before/ all other types of mount instructions (by maintaining a separate queue). That means if you tap on a TextInput to focus it while the screen is doing some heavy rendering, the next time the UIManager executes a batch of instructions, it will execute the focus operation out-of-order, at the very beginning. From a user perspective this is actually quite noticeable, and works much better than the older behavior. # Why it's Not That Dangerous * Is it possible that we'll execute instructions after the corresponding view has disappeared? This was already possible, and is actually less likely now, since it's more likely that the ViewCommand will execute before the Delete instructions executes. * Is it possible we'll execute instructions BEFORE the view is created? Yes, this is possible and I actually found a repro for it. My solution: allow ViewCommands to be retried, exactly once. If they throw an exception the first time, we requeue which will cause the command to be executed after the current batch of mount items. Interestingly, this seems to be unnecessary in Fabric, so the logic there is a bit simpler (probably because on Android we do view preallocation under Fabric, so views are created way before they're inserted into the view hierarchy, and apparently before ViewCommands have a chance to execute). * ViewCommands are already an imperative feature that exists outside of the normal React commit cycle. So they're already dangerous. This doesn't change that, but it does make dangerous code *faster*, so that's good. Changelog: [Android][Changed] ViewCommands on Android now execute earlier, as a perf optimization. Reviewed By: mdvacca Differential Revision: D22343648 fbshipit-source-id: 310d94977ac8ca3140ee8aa272272f660efafa36
React Native
Learn once, write anywhere:
Build mobile apps with React.
Getting Started · Learn the Basics · Showcase · Contribute · Community · Support
React Native brings React's declarative UI framework to iOS and Android. With React Native, you use native UI controls and have full access to the native platform.
- Declarative. React makes it painless to create interactive UIs. Declarative views make your code more predictable and easier to debug.
- Component-Based. Build encapsulated components that manage their state, then compose them to make complex UIs.
- Developer Velocity. See local changes in seconds. Changes to JavaScript code can be live reloaded without rebuilding the native app.
- Portability. Reuse code across iOS, Android, and other platforms.
React Native is developed and supported by many companies and individual core contributors. Find out more in our ecosystem overview.
Contents
- Requirements
- Building your first React Native app
- Documentation
- Upgrading
- How to Contribute
- Code of Conduct
- License
📋 Requirements
React Native apps may target iOS 10.0 and Android 4.1 (API 16) or newer. You may use Windows, macOS, or Linux as your development operating system, though building and running iOS apps is limited to macOS. Tools like Expo can be used to work around this.
🎉 Building your first React Native app
Follow the Getting Started guide. The recommended way to install React Native depends on your project. Here you can find short guides for the most common scenarios:
📖 Documentation
The full documentation for React Native can be found on our website.
The React Native documentation discusses components, APIs, and topics that are specific to React Native. For further documentation on the React API that is shared between React Native and React DOM, refer to the React documentation.
The source for the React Native documentation and website is hosted on a separate repo, @facebook/react-native-website.
🚀 Upgrading
Upgrading to new versions of React Native may give you access to more APIs, views, developer tools, and other goodies. See the Upgrading Guide for instructions.
React Native releases are discussed in the React Native Community, @react-native-community/react-native-releases.
👏 How to Contribute
The main purpose of this repository is to continue evolving React Native core. We want to make contributing to this project as easy and transparent as possible, and we are grateful to the community for contributing bug fixes and improvements. Read below to learn how you can take part in improving React Native.
Code of Conduct
Facebook has adopted a Code of Conduct that we expect project participants to adhere to. Please read the full text so that you can understand what actions will and will not be tolerated.
Contributing Guide
Read our Contributing Guide to learn about our development process, how to propose bugfixes and improvements, and how to build and test your changes to React Native.
Open Source Roadmap
You can learn more about our vision for React Native in the Roadmap.
Good First Issues
We have a list of good first issues that contain bugs which have a relatively limited scope. This is a great place to get started, gain experience, and get familiar with our contribution process.
Discussions
Larger discussions and proposals are discussed in @react-native-community/discussions-and-proposals.
📄 License
React Native is MIT licensed, as found in the LICENSE file.
React Native documentation is Creative Commons licensed, as found in the LICENSE-docs file.