[TOC]
源码解读RCTImageView(iOS)
查看官网自定义UI组件的文档， 可以知道每个自定义的UI组件CustomView需要对应一个CustomViewManager， CustomViewManager继承RCTViewManager.
我们可以跟踪查看requireNativeComponent的实现， 最终发现调用的是UIManager.createView(...), 对应原生RCTUIManager的createView方法。
createView.png
一、RCTUIManager的原理
原生
- RCTUIManager也是一个module， 在setBridge的时候， 获取bridge中所有RCTViewManager的子类保存下来
- (void)setBridge:(RCTBridge *)bridge {
...
for (Class moduleClass in _bridge.moduleClasses) {
if ([moduleClass isSubclassOfClass:[RCTViewManager class]]) {
RCTComponentData *componentData = [[RCTComponentData alloc] initWithManagerClass:moduleClass
bridge:_bridge];
componentDataByName[componentData.name] = componentData;
}
}
_componentDataByName = [componentDataByName copy];
...
}
- constantsToExport把所有相关ViewManager的信息导出
- (NSDictionary *)constantsToExport
{
...
return constants;
}
具体信息格式为：
{
...
RCTImageView = {
Manager = ImageViewManager;
NativeProps = {
blurRadius = CGFloat;
capInsets = UIEdgeInsets;
defaultSource = UIImage;
onError = BOOL;
onLoad = BOOL;
onLoadEnd = BOOL;
onLoadStart = BOOL;
onPartialLoad = BOOL;
onProgress = BOOL;
resizeMode = RCTResizeMode;
source = "NSArray";
tintColor = UIColor;
};
};
RCTWebView = {
Manager = WebViewManager;
NativeProps = {
allowsInlineMediaPlayback = BOOL;
automaticallyAdjustContentInsets = BOOL;
bounces = BOOL;
contentInset = UIEdgeInsets;
dataDetectorTypes = UIDataDetectorTypes;
decelerationRate = CGFloat;
injectedJavaScript = NSString;
mediaPlaybackRequiresUserAction = BOOL;
messagingEnabled = BOOL;
onLoadingError = BOOL;
onLoadingFinish = BOOL;
onLoadingStart = BOOL;
onMessage = BOOL;
onShouldStartLoadWithRequest = BOOL;
scalesPageToFit = BOOL;
scrollEnabled = BOOL;
source = NSDictionary;
};
};
customBubblingEventTypes = {
topBlur = {
phasedRegistrationNames = {
bubbled = onBlur;
captured = onBlurCapture;
};
};
topChange = {
phasedRegistrationNames = {
bubbled = onChange;
captured = onChangeCapture;
};
};
...
};
customDirectEventTypes = {
topAccessibilityTap = {
registrationName = onAccessibilityTap;
};
topError = {
registrationName = onError;
};
...
};
...
}
每个对应的UI组件 xxxView有manager、NativeProps俩个属性。分别表示对应的ViewManager及属性。
JS
//UIManager.js
// 经过映射 UIManager是一个带有上述jsonkey的对象。 同时 会增加Constants 与 UIManager的属性。
UIManager 数据结构
UIManagerjs.png
RCTImageView
原生类的关系图：
RCTImageView.png
js部分
//Image.ios.js
const Image = createReactClass({...,
render:function() {
...
return (
图片定位
Image的图片浏览主要通过source设置， js传递source信息体到原生， 原生根据source信息体生成对应的请求， 通过遍历所有实现的RCTImageURLLoader协议的模块，选择最优的loader获取image，如果没有则尝试使用网络接口获取，失败则报错。 流程如下
getImage.png
source的解析
RN的Image控件，支持2种形式的source
- require('filepath') //PropTypes.number
- {uri:'fileURI', bundle:'bundleName', width:100, height:100, ... } //ImageURISourcePropType
图片控件的JS代码对应Image.ios.js, 原生代码对应RCTImageView
require方式
require方式返回的是一个整型， 对应一个define函数, 在bundle中体现为
//引用的地方 require方式
_react2.default.createElement(_reactNative.Image, { source: require(305 ), __source: { // 305 = ./Images/diary_mood_icon_alcohol_32.png
fileName: _jsxFileName,
lineNumber: 30
}
}),
// uri 方式
_react2.default.createElement(_reactNative.Image, { source: { uir: 'https://www.baidu.com/img/bd_logo1.png', width: 100, height: 100 }, __source: {
fileName: _jsxFileName,
lineNumber: 31
}
})
//define地方
__d(/* RN472/Images/diary_mood_icon_alcohol_32.png */function(global, require, module, exports) {module.exports=require(161 ).registerAsset({"__packager_asset":true,"httpServerLocation":"/assets/Images","width":16,"height":16,"scales":[2,3],"hash":"7824b2f2a263b0bb181ff482a88fb813","name":"diary_mood_icon_alcohol_32","type":"png"}); // 161 = react-native/Libraries/Image/AssetRegistry
}, 305, null, "RN472/Images/diary_mood_icon_alcohol_32.png");
我们看到打包的时候，require图片会转换成如下格式的对象保存:
{
"__packager_asset":true, //是否是asset目录下的资源
"httpServerLocation":"/assets/Images", //server目录地址
"width":16,
"height":16,
"scales":[2,3], //图片scales
"hash":"7824b2f2a263b0bb181ff482a88fb813", //文件hash值
"name":"diary_mood_icon_alcohol_32", //文件名
"type":"png" //文件类型
}
我们看到引用的地方require(305)其实是执行了require(161)的registerAsset的方法。查看161的define
__d(/* AssetRegistry */function(global, require, module, exports) {
'use strict';
var assets = [];
function registerAsset(asset) {
return assets.push(asset);
}
function getAssetByID(assetId) {
return assets[assetId - 1];
}
module.exports = { registerAsset: registerAsset, getAssetByID: getAssetByID };
}, 161, null, "AssetRegistry");
161对应的就是AssetRegistry， AssetRegistry.registerAsset把图片信息保存在成员数组assets中。
查看Image.ios.js的render函数
render: function() {
const source = resolveAssetSource(this.props.source) || { uri: undefined, width: undefined, height: undefined };
...
return (
通过resolveAssetSource函数
function resolveAssetSource(source: any): ?ResolvedAssetSource {
if (typeof source === 'object') {
return source;
}
var asset = AssetRegistry.getAssetByID(source);
if (!asset) {
return null;
}
const resolver = new AssetSourceResolver(getDevServerURL(), getBundleSourcePath(), asset);
if (_customSourceTransformer) {
return _customSourceTransformer(resolver);
}
return resolver.defaultAsset();
调用AssetRegistry.getAssetByID方法取出对应的信息，传递到原生。
//传递到原生的source信息格式
{
"__packager_asset" = 1;
height = 16;
scale = 2;
uri = "//Users/huangmingwei/Library/Developer/CoreSimulator/Devices/2A0C4BE4-807B-4000-83EB-342B720A14DE/data/Containers/Bundle/Application/F84F1359-CBCD-4184-B3FD-2C7833B83A60/RN472.app/react-app/assets/Images/[email protected]";
width = 16;
}
原生通过解析uri信息，获取对应的图片
//RCTImageView.m
- (void)setImageSources:(NSArray *)imageSources
{
if (![imageSources isEqual:_imageSources]) {
_imageSources = [imageSources copy];
[self reloadImage];
}
}
原生加载过程涉到及几个类
- RCTImageSource, 通过js传递的source信息，转换出图片地址
- RCTImageViewManager 管理RCTImageView
- RCTImageVIew 对应每个Image实例
- RCTImageLoader bridge的成员，控制图片的加载逻辑
- RCTImageURLLoader 协议，具体图片的定位执行者需要实现此协议
- RCTLocalAssetImageLoader 实现bundle统计目录asset下的图片访问 loader
重点在RCTImageURLLoader协议
//判断能否处理
- (BOOL)canLoadImageURL:(NSURL *)requestURL;
//获取图片， 如果是异步处理返回一个可以取消的block
- (RCTImageLoaderCancellationBlock)loadImageForURL:(NSURL *)imageURL
size:(CGSize)size
scale:(CGFloat)scale
resizeMode:(RCTResizeMode)resizeMode
progressHandler:(RCTImageLoaderProgressBlock)progressHandler
partialLoadHandler:(RCTImageLoaderPartialLoadBlock)partialLoadHandler
completionHandler:(RCTImageLoaderCompletionBlock)completionHandler;
URI方式
这种方式的加载流程与require相同，只是source的获取信息方式比较简单，js端设置的是什么，到原生端也是一样
function resolveAssetSource(source: any): ?ResolvedAssetSource {
if (typeof source === 'object') { // uri 方式直接返回
return source;
}
原生通过RCTImageSource解析流程是一样的。
Array方式
js端最终将source转换为一个Array，传递到原生。如果有多个uri，可设置为不同尺寸的图片，在原生会选择大小最适合的一个图片展示。 当只有一张图片的时候，默认会转为只有一个元素的Array。目前都是只有一张哦~
RCTImageView.m
- (RCTImageSource *)imageSourceForSize:(CGSize)size
{
if (![self hasMultipleSources]) {
return _imageSources.firstObject;
}
// Need to wait for layout pass before deciding.
if (CGSizeEqualToSize(size, CGSizeZero)) {
return nil;
}
const CGFloat scale = RCTScreenScale();
const CGFloat targetImagePixels = size.width * size.height * scale * scale;
RCTImageSource *bestSource = nil;
CGFloat bestFit = CGFLOAT_MAX;
for (RCTImageSource *source in _imageSources) {
CGSize imgSize = source.size;
const CGFloat imagePixels =
imgSize.width * imgSize.height * source.scale * source.scale;
const CGFloat fit = ABS(1 - (imagePixels / targetImagePixels));
if (fit < bestFit) {
bestFit = fit;
bestSource = source;
}
}
return bestSource;
}