74e54cbcc4
Summary: There seems to be a rounding error in the android code for line height, so that for some fonts and at some combinations of line height and font size the actual height of the elements seems to be slightly too short. I've identified one issue that I mentioned here https://github.com/facebook/react-native/issues/10712#issuecomment-359382137 that could at least explain some of the problem. That when the line-height minus the original sum of the absolute value of top and bottom from the metrics, happens to be an odd number, the division by two causes a rounding error of 1, so that the actual line height is 1pt less than it should. The fix uses floating point division instead of integer division, and rounds (arbitrarily) the negative values up and the positive values down so that the total is still the correct for odd numbers. It turns out that only ascent and descent is used to give the actual line-height between lines in the same text-element. The top and bottom values are only used for padding the top and bottom of the text. So when the line-height is greater than the font size and the extra padding this PR sets the ascent and descent to the same value as the top and bottom respectively. I've renamed the shouldIncreaseAllMetricsProportionally test to evenLineHeightShouldIncreaseAllMetricsProportionally and added an extra assertion to check that bottom-top still equals the line height. Added another test oddLineHeightShouldAlsoWork that is similar but uses an odd number for the line height to test that it still works with odd numbers. This test only uses the sum of the values so that it's indifferent to what value the implementation chooses to round up or down. Improvement on https://github.com/facebook/react-native/pull/16448 Fix line-height calculation on Android. | Before | After | | ------------- |-------------| |  |  | (All three columns have font size 16 and lineHeight: 32. The first one is has fixed height 9*32, the second is 9 Text elements, the last is one text element with lots of text limited to 9 lines, so they should be the same height. ) Closes https://github.com/facebook/react-native/pull/17952 Differential Revision: D6980333 Pulled By: hramos fbshipit-source-id: 0a501358cfbf7f139fca46056d0d972b1daf6ae3 |
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| RNTester | ||
| React | ||
| ReactAndroid | ||
| ReactCommon | ||
| ReactNative | ||
| babel-preset | ||
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| flow | ||
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| gradle/wrapper | ||
| jest | ||
| keystores | ||
| lib | ||
| local-cli | ||
| react-native-cli | ||
| react-native-git-upgrade | ||
| scripts | ||
| third-party-podspecs | ||
| .buckconfig | ||
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| .editorconfig | ||
| .eslintignore | ||
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| .flowconfig | ||
| .gitattributes | ||
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| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
| DockerTests.md | ||
| Jenkinsfile | ||
| LICENSE | ||
| LICENSE-docs | ||
| PATENTS | ||
| README.md | ||
| React.podspec | ||
| Releases.md | ||
| breaking-changes.md | ||
| build.gradle | ||
| cli.js | ||
| gradlew | ||
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| jest-preset.json | ||
| package.json | ||
| react.gradle | ||
| rn-cli.config.js | ||
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README.md
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 Native is BSD licensed. We also provide an additional patent grant.
React Native documentation is Creative Commons licensed.
