如何进行ReactNativeForAndroid框架启动核心路径剖析
如何进行ReactNative For Android 框架启动核心路径剖析,相信很多没有经验的人对此束手无策,为此本文总结了问题出现的原因和解决方法,通过这篇文章希望你能解决这个问题。
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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。
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> { @Override protected void onPreExecute() { if (mCurrentReactContext != null) { tearDownReactContext(mCurrentReactContext); mCurrentReactContext = null; } } @Override protected Result 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 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() { @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() { @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); },
看完上述内容,你们掌握如何进行ReactNative For Android 框架启动核心路径剖析的方法了吗?如果还想学到更多技能或想了解更多相关内容,欢迎关注创新互联行业资讯频道,感谢各位的阅读!
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