Rubén Norte
332355e80f
Summary: Pull Request resolved: https://github.com/facebook/react-native/pull/43581 Changelog: [internal] This implements a mechanism to ensure that JavaScript tasks have a consistent view of the state of the UI during their execution. ## Context Fabric allows committing new revisions of the ShadowTree from any thread, but we don't make use of this capability and instead always commit them from the JS thread (e.g.: when we schedule Fabric state updates to update the offset of a list on scroll). This was done to make sure that JS work didn't see changes in the state of the tree at random points during its execution. E.g.: ``` useEffect(() => { const rect = ref.current.getBoundingClientRect(); // do something const newRect = ref.current.getBoundingClientRect(); // `rect` and `newRect` should always be the same }, []); ``` This isn't used by Reanimated at the moment, which means JS can inadvertently see the result of animations in non-specific times during execution. You can find additional context about this in the [RFC for DOM Traversal & Layout APIs in RN](https://github.com/react-native-community/discussions-and-proposals/blob/main/proposals/0607-dom-traversal-and-layout-apis.md#consistency-and-updates). This works correctly at the moment, but we introduce a limitation in the execution model to prevent updating the tree synchronously from the main thread. One of the main problems this introduces is that computing intersections (for `IntersectionObserver`) relies on the information in the shadow tree, but this is updated asynchronously on scroll. There are 2 potential solutions for that problem: 1) Send the timestamp of the scroll even with the state update to backdate the timestamps of the intersections. This could work but introduces more complexity and possibly accuracy problems due to batching those state updates with other changes (e.g.: what happens if we update the state and commit another tree in the same task? should we use the backdated timestamp or wait for mount?). 2) (**Preferred**/ this diff) Allow committing new revisions from any thread, but lock the JS thread into seeing a specific revision, which would only update/progress in specific moments when it's safe. Some of those moments would be: 1) When we start a new JS task. 2) When we commit a new tree from React (JS). ## Changes This implements the solution outlined in 2), creating a few abstractions to handle what's the current tree that should be visible to JS and to lock/unlock it in specific moments. More specifically: * Creates `ShadowTreeRevisionProvider` as an abstract class for APIs consuming the visible revision of the ShadowTree (mainly DOM APIs and layout methods like `measure`, etc.). * Creates `ShadowTreeRevisionConsistencyManager` as an abstract class to handle what trees are visible (with a `lockRevision` and `unlockRevision` to be called from `RuntimeScheduler` at the beginning and end of each JS task). * Creates 2 different implementations of these abstractions: * One that preserves the current behavior (`LatestShadowTreeRevisionProvider`, which just returns the last committed revision at the time of the call). * One that locks revisions lazily (the first time they're accessed) (`LazyShadowTreeRevisionConsistencyManager`). Reviewed By: sammy-SC Differential Revision: D55024832 fbshipit-source-id: b59985bc83714ae7ec915baba72bf92b3d6fa140
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 13.4 and Android 6.0 (API 23) 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 this discussion repo.
👏 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.