c9aeaf675d
Summary: **Summary:** There was a bug with RN.Dimensions returning incorrect window dimensions. In certain cases when device was in portrait, window dimensions reported landscape dimensions and vice versa. This happened because in certain scenarios, after device orientation changed, dimensions update event from ReactRootView had incorrect dimensions. Was able to reproduce this when device was rotated during app launch. After rotation global layout listener callback gets invoked. Inside the callback current and previous orientations are compared. When a change is detected, orientation and dimension change events are sent to JS. It is assumed, when orientation changes, new dimensions are available immediately. This is not the case for window dimensions as they are retrieved from resources object which gets updated asynchronously after orientation change. In cases when app is doing a lot of work on the main thread, like app startup, it takes more time to update the resources object. And when orientation change is detected in global layout, resources object is not updated with new dimensions yet. This causes dimensions update to be sent to JS with old window dimensions. Global layout listener callback does get invoked a second time when resources object is finally updated with new dimensions, but since orientation no longer changes, no event is sent to JS. Fixed this by separating dimensions update from orientation update. Now RN keeps track of previous window and screen dimension values. When a change is detected, an event is sent to JS with updated dimensions. This ensures that whenever dimensions change, JS gets the updated values. This has a side effect of sending dimension update twice in some cases. One example is the case above where window dimensions take time to update, but screen dimensions are updated immediately. This will cause two events to be sent to JS. One for window dimensions and one for screen dimensions update. Other change is that initial value for both window and screen fields is empty. Which results in first change to trigger an event. Previously initial orientation value was 0 which meant when app started in normal portrait orientation, first layout did not trigger a dimension update event. Now even first layout sends the event. This should not be an issue as it is to make sure dimensions in JS side are correct. **Testing:** Verified with a sample app that correct dimensions are available when app launches. Verified that after orientation dimensions are updated. Verified that in the scenario described above where window dimensions are updated later, we get correct dimension values in JS. We have incorporated this fix into our app and have been testing it internally. Ats Jenk Microsoft Corp. <!-- Thank you for sending the PR! If you changed any code, please provide us with clear instructions on how you verified your changes work. In other words, a test plan is *required*. Bonus points for screenshots and videos! Please read the Contribution Guidelines at https://github.com/facebook/react-native/blob/master/CONTRIBUTING.md to learn more about contributing to React Native. Happy contributing! --> Closes https://github.com/facebook/react-native/pull/15181 Differential Revision: D5552195 Pulled By: shergin fbshipit-source-id: d1f190cb960090468886ff56cda58cac296745db
React Native · 
Learn once, write anywhere: Build mobile apps with React.
- Build native mobile apps using JavaScript and React: React Native lets you build mobile apps using only JavaScript. It uses the same design as React, letting you compose a rich mobile UI from declarative components.
- A React Native app is a real mobile app: With React Native, you don't build a "mobile web app", an "HTML5 app", or a "hybrid app". You build a real mobile app that's indistinguishable from an app built using Objective-C, Java, or Swift. React Native uses the same fundamental UI building blocks as regular iOS and Android apps. You just put those building blocks together using JavaScript and React.
- Don't waste time recompiling: React Native lets you build your app faster. Instead of recompiling, you can reload your app instantly. With hot reloading, you can even run new code while retaining your application state. Give it a try - it's a magical experience.
- Use native code when you need to: React Native combines smoothly with components written in Objective-C, Java, or Swift. It's simple to drop down to native code if you need to optimize a few aspects of your application. It's also easy to build part of your app in React Native, and part of your app using native code directly - that's how the Facebook app works.
The focus of React Native is on developer efficiency across all the platforms you care about - learn once, write anywhere. Facebook uses React Native in multiple production apps and will continue investing in React Native.
See the official React Native website for an introduction to React Native.
Supported operating systems are >= Android 4.1 (API 16) and >= iOS 8.0.
Getting Started
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 website’s documentation is divided into multiple sections.
- There are Guides that discuss topics like debugging, integrating with existing apps, and the gesture responder system.
- The Components section covers React components such as
ViewandButton. - The APIs section covers other libraries like Animated and StyleSheet that aren’t React components themselves.
- Finally, React Native provides a small number of Polyfills that offer web-like APIs.
Another great way to learn more about the components and APIs included with React Native is to read their source. Look under the Libraries/Components directory for components like ScrollView and TextInput, for example. The RNTester example is also here to demonstrate some of the ways to use these components. From the source you can get an accurate understanding of each component’s behavior and API.
The React Native documentation only discusses the components, APIs and topics specific to React Native (React on iOS and Android). For further documentation on the React API that is shared between React Native and React DOM, refer to the React documentation.
Upgrading
React Native is under active development. See the guide on upgrading React Native to keep your project up-to-date.
Contributing
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 bug fixes and improvements, and how to build and test your changes to React Native.
Beginner Friendly Bugs
We have a list of beginner friendly issues to help you get your feet wet in the React Native codebase and familiar with our contribution process. This is a great place to get started.
License
React is BSD licensed. We also provide an additional patent grant.
React documentation is Creative Commons licensed.