【ReactNative For Android】框架启动核心路径剖析

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2017-08-29
原文链接:mp.weixin.qq.com

        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:

        1.通过Builder构建上文概念讲过的NativeModuleRegistry及JavaScriptModuleConfig;

        2.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;

        3.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;

        4.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;

        5.调用reactContext.initializeWithInstance进一步将创建完的CatalystInstance及线程等缓存在ReactContext中;

        6.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 */@Overridepublic 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);},
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