ReactNative For Android 框架启动核心路径剖析

weixin_30859423

54人浏览 · 2016-11-06 13:08:00

weixin_30859423 · 2016-11-06 13:08:00 发布

版权声明：本文由王少鸣原创文章，转载请注明出处:
文章原文链接：https://www.qcloud.com/community/article/144

前面给大家分析过 ReactNative For Android (RN4A) 的通信机制，这次我们从源码出发，分析下RN4A的启动过程。启动过程基于通信机制，涉及通信机制原理大家可以查看前一篇文章，本篇不赘述。

上面是2016 React.js Conf FB 工程师分享的RN启动时序图，整个过程比较清晰，先启动终端运行时，随后由终端上下文去启动JS的运行时，进而布局，最后再由终端进行渲染，最后将View添加到RootView上。那接下来，我们先理解几个概念，方便后续我们对整个启动过程的理解。

模块：

模块即暴露给调用方的API集合，在RN4A存在两种模块。

一种是Native层暴露给Js层的API集合模块，即NativeModule，如ToastModule,DialogModule,或是创建View的UIManagerModule。业务方可以通过实现NativeModule自定义模块，通过重写getName将模块名暴露给Js层，通过注解的方式将API暴露给Js层调用。

另一种是Js层暴露给Java层的API集合模块，即JavascriptModule，如DeviceEventEmitter,AppRegistry等。业务方可以通过继承JavaScriptModule接口自定义接口模块，申明与Js层相应的方法即可。

无论是NativeModule还是JavascriptModule，在Js层存在与之相互映射同名的Module，Js层通过require引用Module。

模块注册表：

各模块信息统一收集到模块注册表。同样，在RN4A中存在两种模块注册表，一是由集合所有Java层模块接口信息的NativeModuleRegistry，另一种是集合所有Js层模块接口信息的JavascriptModuleRegistry。在启动RN4A后，终端将注册表信息存入与前端互通的全局变量__fbBatchedBridgeConfig 中，使得Js层与Java层存在同样的模块注册表。

正如上面FB攻城狮提出的时序图，从终端启动，入口是ReactRootView.startReactApplication，在构造JavaScriptExecutor&JSBundleLoader后，进而通过ReactContextInitAsycnTask去创建ReactContext，这部分主要创建了NativeModules,JavaScriptModule及其对的注册表，负责Js与Java通信的高层接口CatalystInstance等。在创建完ReactContext后，通过CatalystInstance获取AppRegistry并调用其runApplication启动Js Application。整体流程如下：

接下来进入正题，从源码来分析RN4A的启动（为阅读方便，源码适当裁剪）

ReactInstanceManager createReactContextInBackground，通过AysncTask初始化ReactNative上下文。mJSModuleName是与前端约定好所要启动的JS Application Name。mLauncahOptions是终端启动前端Application可选的传入的参数。

/**
 * ReactRootView.java
 */
public void startReactApplication( ReactInstanceManager reactInstanceManager, String moduleName, @Nullable Bundle launchOptions) { UiThreadUtil.assertOnUiThread(); mReactInstanceManager = reactInstanceManager; mJSModuleName = moduleName; mLaunchOptions = launchOptions; if (!mReactInstanceManager.hasStartedCreatingInitialContext()) { mReactInstanceManager.createReactContextInBackground(); } if (mWasMeasured && mIsAttachedToWindow) { mReactInstanceManager.attachMeasuredRootView(this); mIsAttachedToInstance = true; getViewTreeObserver().addOnGlobalLayoutListener(getKeyboardListener()); } else { mAttachScheduled = true; } } `

createReactContextInBackground最终调用到recreateReactContextInBackgroundFromBundleFile。这里会创建两个Key Obj : JSCJavaScriptExecutor&JSBundleLoader。
JSCJavaScriptExecutor继承自JavaScriptExecutor，在JSCJavaScriptExecutor.class加载会加载ReactNative的SO，并且，在初始JSCJavaScriptExecutor时会调用initialze去初始C++层ReactNative与JSC的通信框架等。
JSBundleLoader缓存了JsBundle的信息，封装了上层加载JsBundle相关接口，CatalystInstance通过其间接调用ReactBridge去加载文件。

/**
 * ReactInstanceManagerImpl.java
 */
private void recreateReactContextInBackgroundFromBundleFile() { recreateReactContextInBackground( new JSCJavaScriptExecutor.Factory(), JSBundleLoader.createFileLoader(mApplicationContext, mJSBundleFile)); }

创建完JSCJavaScriptExecutor&JSBundleLoader后，execute ReactContextInitAsyncTask继续初始化ReactContext。

/**
 * ReactInstanceManagerImpl.java
 */
private void recreateReactContextInBackground( JavaScriptExecutor.Factory jsExecutorFactory, JSBundleLoader jsBundleLoader) { ReactContextInitParams initParams = new ReactContextInitParams(jsExecutorFactory, jsBundleLoader); if (!mIsContextInitAsyncTaskRunning) { ReactContextInitAsyncTask initTask = new ReactContextInitAsyncTask(); initTask.execute(initParams); mIsContextInitAsyncTaskRunning = true; } else { mPendingReactContextInitParams = initParams; } }

ReactContextInitAsyncTask为创建ReactContext的核心类，在执行初始化前会销毁先前的上下文，保证只存在一个上下文。随后，调用createReactContext进一步创建ReactContext。在创建完React Context后会调用setUpReactContext，进而通知DevSupportManager更新上下文，更新生命周期，将ReactRootView做为Root View传递给UIManagerModule，调用AppRegistry的runApplication去启动Js Application等。

/**
 * ReactInstanceManagerImpl$ReactContextInitAsynTask.java
 */
private final class ReactContextInitAsyncTask extends AsyncTask<ReactContextInitParams, Void, Result<ReactApplicationContext>> { @Override protected void onPreExecute() { if (mCurrentReactContext != null) { tearDownReactContext(mCurrentReactContext); mCurrentReactContext = null; } } @Override protected Result<ReactApplicationContext> doInBackground(ReactContextInitParams... params) { Assertions.assertCondition(params != null && params.length > 0 && params[0] != null); try { JavaScriptExecutor jsExecutor = params[0].getJsExecutorFactory().create(); return Result.of(createReactContext(jsExecutor, params[0].getJsBundleLoader())); } catch (Exception e) { // Pass exception to onPostExecute() so it can be handled on the main thread return Result.of(e); } } @Override protected void onPostExecute(Result<ReactApplicationContext> result) { try { setupReactContext(result.get()); } catch (Exception e) { mDevSupportManager.handleException(e); } finally { mIsContextInitAsyncTaskRunning = false; } // Handle enqueued request to re-initialize react context. if (mPendingReactContextInitParams != null) { recreateReactContextInBackground( mPendingReactContextInitParams.getJsExecutorFactory(), mPendingReactContextInitParams.getJsBundleLoader()); mPendingReactContextInitParams = null; } } }

在CreateReactContext中，主要有以下5个key path:

通过Builder构建上文概念讲过的NativeModuleRegistry及JavaScriptModuleConfig；
创建ReactApplicationContext。ReactApplicationContext继承自ContextWrapper，主要缓存了Application Context，Activity Context，ReactNative处理消息的三个thread(下篇讲述)，还有就是全局控制JS调用导致Native Module Crash的NativeModuleCallExceptionHandler，在初始化ReactInstanceManager的时候传入，并且要关闭DeveloperSupport后才可以启用，假如不传，则默认交由DevSupportManger去处理；
创建ReactPackage。ReactPackage主要通过createNativeModules、createJSModules和createViewManagers等API去创建本地模块，JS模块及视图组件等。ReactPackage分为framework的CoreModulesPackage和业务方可选的基础MainReactPackage，CoreModulesPackage封装了大部分通信，调试核心类，如UIManagerModule，这个负责控制Js层Dom到Native View的核心类；
创建CatalystInstance。CatalystInstance并不直接面向开发者，开发者通ReactInstanceManger间接操作CatalystInstance。CatalystInstance持有对ReactBridge的引用，主要通过ReactBridge这个JNI类去实现Java层与Js层的通信，ReactBridge由CatalystInstance的Constructor创建。同时初始化的时候调用了ReactQueueConfigurationSpec.createDefault创建了ReactNative通信的两个线程 JsQueueThread&NativeModulesQueueThread；
调用reactContext.initializeWithInstance进一步将创建完的CatalystInstance及线程等缓存在ReactContext中；
调用catalystInstance.runJSBundle加载解析Jsbundle；

/**
 * ReactInstanceManagerImpl.java
 *
 * @return instance of {@link ReactContext} configured a {@link CatalystInstance} set
 */
private ReactApplicationContext createReactContext( JavaScriptExecutor jsExecutor, JSBundleLoader jsBundleLoader) { mSourceUrl = jsBundleLoader.getSourceUrl(); NativeModuleRegistry.Builder nativeRegistryBuilder = new NativeModuleRegistry.Builder(); JavaScriptModulesConfig.Builder jsModulesBuilder = new JavaScriptModulesConfig.Builder(); ReactApplicationContext reactContext = new ReactApplicationContext(mApplicationContext); if (mUseDeveloperSupport) { reactContext.setNativeModuleCallExceptionHandler(mDevSupportManager); } CoreModulesPackage coreModulesPackage = new CoreModulesPackage(this, mBackBtnHandler, mUIImplementationProvider); processPackage(coreModulesPackage, reactContext, nativeRegistryBuilder, jsModulesBuilder); for (ReactPackage reactPackage : mPackages) { processPackage(reactPackage, reactContext, nativeRegistryBuilder, jsModulesBuilder); } nativeModuleRegistry = nativeRegistryBuilder.build(); javaScriptModulesConfig = jsModulesBuilder.build(); NativeModuleCallExceptionHandler exceptionHandler = mNativeModuleCallExceptionHandler != null ? mNativeModuleCallExceptionHandler : mDevSupportManager; CatalystInstanceImpl.Builder catalystInstanceBuilder = new CatalystInstanceImpl.Builder() .setReactQueueConfigurationSpec(ReactQueueConfigurationSpec.createDefault()) .setJSExecutor(jsExecutor) .setRegistry(nativeModuleRegistry) .setJSModulesConfig(javaScriptModulesConfig) .setJSBundleLoader(jsBundleLoader) .setNativeModuleCallExceptionHandler(exceptionHandler); CatalystInstance catalystInstance= catalystInstanceBuilder.build(); if (mBridgeIdleDebugListener != null) { catalystInstance.addBridgeIdleDebugListener(mBridgeIdleDebugListener); } reactContext.initializeWithInstance(catalystInstance); catalystInstance.runJSBundle(); return reactContext; }

ReactBridge由CatalystInstance的Constructor创建。

/**
 *  CatalystInstanceImpl.java
 */
private CatalystInstanceImpl( final ReactQueueConfigurationSpec ReactQueueConfigurationSpec, final JavaScriptExecutor jsExecutor, final NativeModuleRegistry registry, final JavaScriptModulesConfig jsModulesConfig, final JSBundleLoader jsBundleLoader, NativeModuleCallExceptionHandler nativeModuleCallExceptionHandler) { mReactQueueConfiguration = ReactQueueConfigurationImpl.create( ReactQueueConfigurationSpec, new NativeExceptionHandler()); mBridgeIdleListeners = new CopyOnWriteArrayList<>(); mJavaRegistry = registry; mJSModuleRegistry = new JavaScriptModuleRegistry(CatalystInstanceImpl.this, jsModulesConfig); mJSBundleLoader = jsBundleLoader; mNativeModuleCallExceptionHandler = nativeModuleCallExceptionHandler; mTraceListener = new JSProfilerTraceListener(); try { mBridge = mReactQueueConfiguration.getJSQueueThread().callOnQueue( new Callable<ReactBridge>() { @Override public ReactBridge call() throws Exception { Systrace.beginSection(Systrace.TRACE_TAG_REACT_JAVA_BRIDGE, "initializeBridge"); try { return initializeBridge(jsExecutor, jsModulesConfig); } finally { Systrace.endSection(Systrace.TRACE_TAG_REACT_JAVA_BRIDGE); } } }).get(); } catch (Exception t) { throw new RuntimeException("Failed to initialize bridge", t); } }

ReactBridge将注册表信息存入与前端互通的全局变量 __fbBatchedBridgeConfig 中，使得Js层与Java层存在同样的模块注册表。

/**
 *  CatalystInstanceImpl.java
 */
private ReactBridge initializeBridge( JavaScriptExecutor jsExecutor, JavaScriptModulesConfig jsModulesConfig) { ReactBridge bridge = new ReactBridge(jsExecutor, new NativeModulesReactCallback(), mReactQueueConfiguration.getNativeModulesQueueThread()); Systrace.beginSection(Systrace.TRACE_TAG_REACT_JAVA_BRIDGE, "setBatchedBridgeConfig"); bridge.setGlobalVariable( "__fbBatchedBridgeConfig", buildModulesConfigJSONProperty(mJavaRegistry, jsModulesConfig)); bridge.setGlobalVariable( "__RCTProfileIsProfiling", return bridge; }

调用catalystInstance.runJSBundle加载解析Jsbundle。假如在解析过程中出现Exception，统一交给NativeModuleCallExceptionHandler处理，建议开发者设置自己的NativeModuleCallExceptionHandler，可以归避部分Crash（SyntaxError: Unexpected token ‘<‘ 或 SyntaxError: Unexpected end of script）。

/**
 *  CatalystInstanceImpl.java
 */
public void runJSBundle() { try { mJSBundleHasLoaded = mReactQueueConfiguration.getJSQueueThread().callOnQueue( new Callable<Boolean>() { @Override public Boolean call() throws Exception { incrementPendingJSCalls(); try { mJSBundleLoader.loadScript(mBridge); Systrace.registerListener(mTraceListener); } catch (JSExecutionException e) { mNativeModuleCallExceptionHandler.handleException(e); } finally { Systrace.endSection(Systrace.TRACE_TAG_REACT_JAVA_BRIDGE); } return true; } }).get(); } catch (Exception t) { throw new RuntimeException(t); } }

在创建完React Context后会执行ReactContextInitAsyncTask的onPostExecute，从而调用setUpReactContext，会将ReactRootView做为Root View传递给UIManagerModule，此后Js通过UIManager创建的View都会add到该View上。

/**
 * ReactInstanceManagerImpl.java
 */
@Override
public void attachMeasuredRootView(ReactRootView rootView) { UiThreadUtil.assertOnUiThread(); if(mIsNeedDetachView){ Log.d(ReactConstants.QZONE_REACT_SRC_TAG,"attachMeasuredRootView do add"); mAttachedRootViews.add(rootView); // If react context is being created in the background, JS application will be started // automatically when creation completes, as root view is part of the attached root view list. if (!mIsContextInitAsyncTaskRunning && mCurrentReactContext != null) { attachMeasuredRootViewToInstance(rootView, mCurrentReactContext.getCatalystInstance()); } }else{ Log.d(ReactConstants.QZONE_REACT_SRC_TAG,"attachMeasuredRootView do nothing"); } }

在绑定完RootView后，通过CatalystInstance获取AppRegistry这个JSModule后，进一步调用runApplication启动Js Application。

/**
 * ReactInstanceManagerImpl.java
 */
private void attachMeasuredRootViewToInstance( ReactRootView rootView, CatalystInstance catalystInstance) { rootView.removeAllViews(); rootView.setId(View.NO_ID); UIManagerModule uiManagerModule = catalystInstance.getNativeModule(UIManagerModule.class); int rootTag = uiManagerModule.addMeasuredRootView(rootView); @Nullable Bundle launchOptions = rootView.getLaunchOptions(); WritableMap initialProps = launchOptions != null ? Arguments.fromBundle(launchOptions) : Arguments.createMap(); String jsAppModuleName = rootView.getJSModuleName(); WritableNativeMap appParams = new WritableNativeMap(); appParams.putDouble("rootTag", rootTag); appParams.putMap("initialProps", initialProps); catalystInstance.getJSModule(AppRegistry.class).runApplication(jsAppModuleName, appParams); }

ReactNative中Java与Js通信不再赘述。至此，启动Js层AppRegistry的runApplication启动Js Application。

/**
* AppRegistry.js
*/
runApplication: function(appKey: string, appParameters: any): void { console.log( 'Running application "' + appKey + '" with appParams: ' + JSON.stringify(appParameters) + '. ' + '__DEV__ === ' + String(__DEV__) + ', development-level warning are ' + (__DEV__ ? 'ON' : 'OFF') + ', performance optimizations are ' + (__DEV__ ? 'OFF' : 'ON') ); invariant( runnables[appKey] && runnables[appKey].run, 'Application ' + appKey + ' has not been registered. This ' + 'is either due to a require() error during initialization ' + 'or failure to call AppRegistry.registerComponent.' ); runnables[appKey].run(appParameters); },