Bartol Karuza
3f1b021506
Summary: We noticed that on Android the lineHeight behaviour is different from iOS for built in fonts and custom fonts. The problem becomes visible when the lineHeight approaches the fontSize, showing a cut-off on the bottom of the TextView. This issue has been raised before in #10712. There is a mention of a PR with a fix in that issue, which has not been merged yet. This implementation is a less intrusive fix leaving the current lineHeight approach in place and fixing the discrepancy only. This proposed change prioritises ascent over descent for reduction, making the lineHeight functionality behave identical to iOS. There is no existing test covering the lineHeight property and its behaviour in the CustomLineHeightSpan. This PR contains new unit tests that covers the various scenario's for the lineHeight calculations. The original behaviour, before the change can against these unit tests. The case that fails is `shouldReduceAscentThird`, which can be made to succeed on the old code by changing the asserts to: ``` assertThat(fm.top).isEqualTo(-5); assertThat(fm.ascent).isEqualTo(-5); assertThat(fm.descent).isEqualTo(-4); assertThat(fm.bottom).isEqualTo(-4); ``` The unit test succeeds for the current implementation, which has the values for ascent and descent inverted. Below screenshots show before, after and iOS: BEFORE  AFTER  iOS  [ANDROID] [BUGFIX] [Text] - Fix the lineHeight behaviour on Android to match iOS Closes https://github.com/facebook/react-native/pull/16448 Differential Revision: D6221854 Pulled By: andreicoman11 fbshipit-source-id: 7292f0f05f212d79678ac9d73e8a46bf93f1a7c6
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
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Contributing Guide
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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 Native is BSD licensed. We also provide an additional patent grant.
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