54f7eb3424
Summary:
This PR increases the speed at which cached images are loaded and displayed on the screen. Images are currently cached in memory using RCTImageCache, but each time they are loaded, a round trip through RCTNetworking happens before RCTImageCache is even checked. This is likely so that RCTNetworking can handle the caching behavior required by the HTTP headers. However, this means that at the very least, images are read from disk each time they're loaded.
This PR makes RCTImageLoader check RCTImageCache _before_ sending a request to RCTNetworking. RCTImageCache stores a bit of information about the response headers so that it can respect Cache-Control fields without needing a roundtrip through RCTNetworking.
Here are a couple of graphs showing improved loading times before this change (blue) and after (red) with SDWebImage (yellow) as a baseline comparison. The increase is most evident when loading especially large (hi-res photo size) images, or loading multiple images at a time.
https://imgur.com/a/cnL47Z0
More performance gains can potentially be had by increasing the size limit of RCTImageCache: 1a6666a116/Libraries/Image/RCTImageCache.m (L39) but this comes at the tradeoff of being more likely to run into OOM crashes.
Pull Request resolved: https://github.com/facebook/react-native/pull/20356
Reviewed By: PeteTheHeat
Differential Revision: D12909121
Pulled By: alsun2001
fbshipit-source-id: 7f5e21928c53d7aa53f293b7f1b4ec5c99b5f0c2
React Native · 
Learn once, write anywhere: Build mobile apps with React.
See the official React Native website for an introduction to React Native.
Requirements
Supported target operating systems are >= Android 4.1 (API 16) and >= iOS 9.0. You may use Windows, macOS, or Linux as your development operating system, though building and running iOS apps is limited to macOS by default (tools like Expo can be used to get 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:
How React Native works
React Native lets you build mobile apps using JavaScript. It uses the same design as React, letting you compose a rich mobile UI from declarative components.
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, Kotlin, 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.
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.
React Native combines smoothly with components written in Objective-C, Java, Kotlin, 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.
Full documentation
The full documentation for React Native can be found on our website. The source for the React Native documentation and website is hosted on a separate repo, https://github.com/facebook/react-native-website.
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.
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See the CONTRIBUTING file for how to help out.
License
React Native is MIT licensed, as found in the LICENSE file.
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