React Native之底层源码分析篇
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学习React-Native有一段时间了。今天就从源码的角度来分析下React-Native底层的通信机制。了解下底层是如何通信的对开发也有所好处。
概要
先大概讲一下React-Native的通信过程。RN主要的通信在于java与js之间，平常我们写的jsx代码最终会调用到原生的View。上一篇博客我们也了解到了要新建一个原生模块需要在java层和js层分别写一个Module，那这彼此之间联系是如何实现的呢？
层次结构
RN总共分为三层，java层，C++层，js层。借用一幅图来看下：
Java层：java层就是app原生代码，它通过启动C++层的javascript解析器javascriptCore来执行js代码，从而构建原生UI等。java层依赖于众多优秀开源库，在图片处理使用的是Fresco，网络通信使用的是okhttp，Json解析工具用jackson,动画库用NineOldandroids等，在java层原生的功能均封装为Module，如Toast和Log等。
C++层：c++层最主要是封装了JavaScriptCore，它是一个全新的支持ES6的webKit。Bridge连接了java与js之间的通信。解析js文件是通过JSCExectutor进行的。
Js层：主要处理事件分发及UI Layout，平常开发最常用的。通用jsx来写业务代码，通过flexbox来实现布局。不依赖DOM。由于react有 DOM diff这个算法，所以它的效率非常高。
通信机制
在Java层与Js层的bridge分别存有相同一份模块配置表，Java与Js互相通信时，通过将里配置表中的moduleID，methodID转换成json数据的形式传递给到C++层，C++层传送到js层，通过js层的的模块配置表找到对应的方法进行执行，如果有callback，则回传给java层。这里只是大概介绍，后面会有详细讲解。
主要流程与主要类
先看下java层的流程图：
- ReactInstanceManager：主要是用来创建及管理CatalyInstance的实例的上层接口，控制开发调试，生命周期与ReactRootView所在activity保持一致。
- ReactRootView：为启动入口核心类，负责监听及分发事件并重新渲染元素，App启动后，其将作为App的root view。
- CatalystInstance：提供Java与Js互通的环境，创建Java模块注册表及Javascript模块注册表，并遍历实例化模块，最后通过ReactBridge将Js Bundle传送到Js引擎。
- JSBuilderLoader: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。
- NativeModuleRegistry：Java层模块注册表，即暴露给Js的API集合。
- JavascriptModuleRegistry：Js层模块注册表，负责将所有JavaScriptModule注册到CatalystInstance。
- CoreModulePackage：CoreModulesPackage里面定义了RN框架核心的一些Java和JS的module，创建NativeModules&JsModules组件模块。
源码分析
加载Module
首先看MainActivity的
protected List<ReactPackage> getPackages()
return Arrays.<ReactPackage>asList(
new MainReactPackage(),
new AppReactPackage()
);
AppReactPackage是我们自定义的一个ReactPackage，也就是说如果自己定义了新组件，要在这里添加。看下ReactActivity，看它的onCreate方法：
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
if(this.getUseDeveloperSupport() && VERSION.SDK_INT >= 23 && !Settings.canDrawOverlays(this))
Intent mReactRootView = new Intent("android.settings.action.MANAGE_OVERLAY_PERMISSION");
this.startActivity(mReactRootView);
FLog.w("React", "Overlay permissions needs to be granted in order for react native apps to run in dev mode");
Toast.makeText(this, "Overlay permissions needs to be granted in order for react native apps to run in dev mode", 1).show();
this.mReactInstanceManager = this.createReactInstanceManager();
ReactRootView mReactRootView1 = this.createRootView();
mReactRootView1.startReactApplication(this.mReactInstanceManager, this.getMainComponentName(), this.getLaunchOptions());
this.setContentView(mReactRootView1);
主要完成三个功能，通过createReactInstanceManager创建ReactInstanceManager,它主要是用来创建及管理CatalyInstance的实例的上层接口。第二步是通过createRootView来创建ReactRootView。最后调用ReactRootView的startReactApplication来启动应用，并把它当作rootview setContentView到界面上。重点看startReactApplication方法：
public void startReactApplication(ReactInstanceManager reactInstanceManager, String moduleName, @Nullable Bundle launchOptions)
UiThreadUtil.assertOnUiThread();
Assertions.assertCondition(this.mReactInstanceManager == null, "This root view has already been attached to a catalyst instance manager");
this.mReactInstanceManager = reactInstanceManager;
this.mJSModuleName = moduleName;
this.mLaunchOptions = launchOptions;
if(!this.mReactInstanceManager.hasStartedCreatingInitialContext())
this.mReactInstanceManager.createReactContextInBackground();
if(this.mWasMeasured && this.mIsAttachedToWindow)
this.mReactInstanceManager.attachMeasuredRootView(this);
this.mIsAttachedToInstance = true;
this.getViewTreeObserver().addOnGlobalLayoutListener(this.getKeyboardListener());
else
this.mAttachScheduled = true;
mJSModuleName是与前端约定好所要启动的JS Application Name。先看createReactContextInBackground方法，它位于ReactInstanceManager的实现类ReactInstanceManagerImpl中：
public void recreateReactContextInBackground()
Assertions.assertCondition(this .mHasStartedCreatingInitialContext , "recreateReactContextInBackground should only be called after the initial createReactContextInBackground call.") ;
this. recreateReactContextInBackgroundInner() ;
createReactContextInBackground最终调用到recreateReactContextInBackgroundInner：
private void recreateReactContextInBackgroundInner()
UiThreadUtil.assertOnUiThread();
if( this.mUseDeveloperSupport && this.mJSMainModuleName != null)
if (this.mDevSupportManager.hasUpToDateJSBundleInCache())
this .onJSBundleLoadedFromServer() ;
else if(this .mJSBundleFile == null)
this .mDevSupportManager.handleReloadJS() ;
else
this .mDevSupportManager.isPackagerRunning( new PackagerStatusCallback()
public void onPackagerStatusFetched( final boolean packagerIsRunning)
UiThreadUtil.runOnUiThread( new Runnable()
public void run()
if(packagerIsRunning)
ReactInstanceManagerImpl.this .mDevSupportManager.handleReloadJS() ;
else
ReactInstanceManagerImpl.this .recreateReactContextInBackgroundFromBundleFile() ;
) ;
);
else
this .recreateReactContextInBackgroundFromBundleFile() ;
接着调用recreateReactContextInBackgroundFromBundleFile：
private void recreateReactContextInBackgroundFromBundleFile()
this.recreateReactContextInBackground(new com.facebook.react.bridge.JSCJavaScriptExecutor.Factory(), JSBundleLoader.createFileLoader(this.mApplicationContext, this.mJSBundleFile));
经过一系列的周转，最后调用到了recreateReactContextInBackground：
private void recreateReactContextInBackground(com.facebook.react.bridge.JavaScriptExecutor.Factory jsExecutorFactory, JSBundleLoader jsBundleLoader)
UiThreadUtil.assertOnUiThread();
ReactInstanceManagerImpl.ReactContextInitParams initParams = new ReactInstanceManagerImpl.ReactContextInitParams(jsExecutorFactory , jsBundleLoader);
if( this.mReactContextInitAsyncTask == null)
this .mReactContextInitAsyncTask = new ReactInstanceManagerImpl.ReactContextInitAsyncTask( null);
this.mReactContextInitAsyncTask.execute( new ReactInstanceManagerImpl.ReactContextInitParams[]initParams) ;
else
this .mPendingReactContextInitParams = initParams ;
上面代码通过ReactContextInitAsyncTask这个AsyncTask来初始化ReactCotext。
private final class ReactContextInitAsyncTask extends AsyncTask<ReactInstanceManagerImpl.ReactContextInitParams, Void, ReactInstanceManagerImpl.Result<ReactApplicationContext>>
private ReactContextInitAsyncTask()
protected void onPreExecute()
if(ReactInstanceManagerImpl.this.mCurrentReactContext != null)
ReactInstanceManagerImpl.this.tearDownReactContext(ReactInstanceManagerImpl.this.mCurrentReactContext);
ReactInstanceManagerImpl.this.mCurrentReactContext = null;
protected ReactInstanceManagerImpl.Result<ReactApplicationContext> doInBackground(ReactInstanceManagerImpl.ReactContextInitParams... params)
Assertions.assertCondition(params != null && params.length > 0 && params[0] != null);
try
JavaScriptExecutor e = params[0].getJsExecutorFactory().create(ReactInstanceManagerImpl.this.mJSCConfig == null?new WritableNativeMap():ReactInstanceManagerImpl.this.mJSCConfig.getConfigMap());
return ReactInstanceManagerImpl.Result.of((Object)ReactInstanceManagerImpl.this.createReactContext(e, params[0].getJsBundleLoader()));
catch (Exception var3)
return ReactInstanceManagerImpl.Result.of(var3);
protected void onPostExecute(ReactInstanceManagerImpl.Result<ReactApplicationContext> result)
try
ReactInstanceManagerImpl.this.setupReactContext((ReactApplicationContext)result.get());
catch (Exception var6)
ReactInstanceManagerImpl.this.mDevSupportManager.handleException(var6);
finally
ReactInstanceManagerImpl.this.mReactContextInitAsyncTask = null;
if(ReactInstanceManagerImpl.this.mPendingReactContextInitParams != null)
ReactInstanceManagerImpl.this.recreateReactContextInBackground(ReactInstanceManagerImpl.this.mPendingReactContextInitParams.getJsExecutorFactory(), ReactInstanceManagerImpl.this.mPendingReactContextInitParams.getJsBundleLoader());
ReactInstanceManagerImpl.this.mPendingReactContextInitParams = null;
ReactContextInitAsyncTask为创建ReactContext的核心类，随后，调用createReactContext进一步创建ReactContext。在创建完React Context后会调用setUpReactContext，将ReactRootView做为Root View传递给UIManagerModule，调用AppRegistry的runApplication去启动Js Application等。看createReactContext的代码：
private ReactApplicationContext createReactContext(JavaScriptExecutor jsExecutor , JSBundleLoader jsBundleLoader)
FLog.i("React" , "Creating react context.");
ReactMarker.logMarker( "CREATE_REACT_CONTEXT_START" );
this.mSourceUrl = jsBundleLoader.getSourceUrl() ;
Builder nativeRegistryBuilder = new Builder();
com.facebook.react.bridge.JavaScriptModulesConfig.Builder jsModulesBuilder = new com.facebook.react.bridge.JavaScriptModulesConfig.Builder() ;
ReactApplicationContext reactContext = new ReactApplicationContext( this.mApplicationContext);
if( this.mUseDeveloperSupport)
reactContext.setNativeModuleCallExceptionHandler(this.mDevSupportManager) ;
ReactMarker.logMarker("PROCESS_PACKAGES_START" );
Systrace.beginSection( 0L, "createAndProcessCoreModulesPackage" );
try
CoreModulesPackage nativeModuleRegistry = new CoreModulesPackage( this, this.mBackBtnHandler , this.mUIImplementationProvider);
this.processPackage(nativeModuleRegistry , reactContext, nativeRegistryBuilder, jsModulesBuilder) ;
finally
Systrace.endSection(0L );
Iterator nativeModuleRegistry2 = this .mPackages.iterator();
while(nativeModuleRegistry2.hasNext())
ReactPackage javaScriptModulesConfig = (ReactPackage)nativeModuleRegistry2.next();
Systrace.beginSection( 0L, "createAndProcessCustomReactPackage" );
try
this .processPackage(javaScriptModulesConfig , reactContext, nativeRegistryBuilder, jsModulesBuilder) ;
finally
Systrace.endSection(0L) ;
ReactMarker.logMarker("PROCESS_PACKAGES_END" );
ReactMarker.logMarker( "BUILD_NATIVE_MODULE_REGISTRY_START" );
Systrace.beginSection( 0L, "buildNativeModuleRegistry" );
NativeModuleRegistry nativeModuleRegistry1 ;
try
nativeModuleRegistry1 = nativeRegistryBuilder.build();
finally
Systrace.endSection(0L );
ReactMarker.logMarker( "BUILD_NATIVE_MODULE_REGISTRY_END" );
ReactMarker.logMarker("BUILD_JS_MODULE_CONFIG_START" );
Systrace.beginSection( 0L, "buildJSModuleConfig" );
JavaScriptModulesConfig javaScriptModulesConfig1 ;
try
javaScriptModulesConfig1 = jsModulesBuilder.build();
finally
Systrace.endSection(0L );
ReactMarker.logMarker( "BUILD_JS_MODULE_CONFIG_END" );
Object exceptionHandler = this .mNativeModuleCallExceptionHandler != null?this .mNativeModuleCallExceptionHandler: this.mDevSupportManager;
com.facebook.react.bridge.CatalystInstanceImpl.Builder catalystInstanceBuilder = ( new com.facebook.react.bridge.CatalystInstanceImpl.Builder()).setReactQueueConfigurationSpec(ReactQueueConfigurationSpec.createDefault()).setJSExecutor(jsExecutor).setRegistry(nativeModuleRegistry1).setJSModulesConfig(javaScriptModulesConfig1).setJSBundleLoader(jsBundleLoader).setNativeModuleCallExceptionHandler((NativeModuleCallExceptionHandler)exceptionHandler) ;
ReactMarker.logMarker( "CREATE_CATALYST_INSTANCE_START" );
Systrace.beginSection( 0L, "createCatalystInstance" );
CatalystInstanceImpl catalystInstance ;
try
catalystInstance = catalystInstanceBuilder.build();
finally
Systrace.endSection(0L );
ReactMarker.logMarker( "CREATE_CATALYST_INSTANCE_END" );
if (this.mBridgeIdleDebugListener != null)
catalystInstance.addBridgeIdleDebugListener(this.mBridgeIdleDebugListener) ;
reactContext.initializeWithInstance(catalystInstance);
ReactMarker.logMarker( "RUN_JS_BUNDLE_START" );
Systrace.beginSection( 0L, "runJSBundle" );
try
catalystInstance.runJSBundle();
finally
Systrace.endSection(0L );
ReactMarker.logMarker( "RUN_JS_BUNDLE_END" );
return reactContext;
代码很长，我们来分段分析。
第一步
com.facebook.react.bridge.JavaScriptModulesConfig.Builder jsModulesBuilder = new com.facebook.react.bridge.JavaScriptModulesConfig.Builder();创建JavaScriptModulesConfig。
第二步
ReactApplicationContext reactContext = new ReactApplicationContext(this.mApplicationContext);创建ReactApplicationContext上下文。
第三步
try
CoreModulesPackage nativeModuleRegistry = new CoreModulesPackage(this, this.mBackBtnHandler, this.mUIImplementationProvider);
this.processPackage(nativeModuleRegistry, reactContext, nativeRegistryBuilder, jsModulesBuilder);
finally
Systrace.endSection(0L);
Iterator nativeModuleRegistry2 = this.mPackages.iterator();
while(nativeModuleRegistry2.hasNext())
ReactPackage javaScriptModulesConfig = (ReactPackage)nativeModuleRegistry2.next();
Systrace.beginSection(0L, "createAndProcessCustomReactPackage");
try
this.processPackage(javaScriptModulesConfig, reactContext, nativeRegistryBuilder, jsModulesBuilder);
finally
Systrace.endSection(0L);
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；看下processPackage方法：
private void processPackage(ReactPackage reactPackage, ReactApplicationContext reactContext, Builder nativeRegistryBuilder, com.facebook.react.bridge.JavaScriptModulesConfig.Builder jsModulesBuilder)
Iterator i$ = reactPackage.createNativeModules(reactContext).iterator();
while(i$.hasNext())
NativeModule jsModuleClass = (NativeModule)i$.next();
nativeRegistryBuilder.add(jsModuleClass);
i$ = reactPackage.createJSModules().iterator();
while(i$.hasNext())
Class jsModuleClass1 = (Class)i$.next();
jsModulesBuilder.add(jsModuleClass1);
很简单，拿到具体的native和JS的module把它们添加到对应的builder中。先是添加CoreModulesPackage中的module再添加我们自定义的module，先看CoreModulesPackage中的createNativeModules方法：
public List<NativeModule> createNativeModules(ReactApplicationContext catalystApplicationContext)
Systrace.beginSection(0L, "createUIManagerModule");
UIManagerModule uiManagerModule;
try
List viewManagersList = this.mReactInstanceManager.createAllViewManagers(catalystApplicationContext);
uiManagerModule = new UIManagerModule(catalystApplicationContext, viewManagersList, this.mUIImplementationProvider.createUIImplementation(catalystApplicationContext, viewManagersList));
finally
Systrace.endSection(0L);
return Arrays.asList(new NativeModule[]new AnimationsDebugModule(catalystApplicationContext, this.mReactInstanceManager.getDevSupportManager().getDevSettings()), new AndroidInfoModule(), new DeviceEventManagerModule(catalystApplicationContext, this.mHardwareBackBtnHandler), new ExceptionsManagerModule(this.mReactInstanceManager.getDevSupportManager()), new Timing(catalystApplicationContext), new SourceCodeModule(this.mReactInstanceManager.getSourceUrl(), this.mReactInstanceManager.getDevSupportManager().getSourceMapUrl()), uiManagerModule, new DebugComponentOwnershipModule(catalystApplicationContext));
就是将UIManagerModule、AnimationsDebugModule等装到build中。
接着添加我们自定义的组件，以自定义Log为例，需要如下内容吗：
public class AppReactPackage implements ReactPackage
@Override
public List<NativeModule> createNativeModules(ReactApplicationContext reactApplicationContext)
List<NativeModule> modules=new ArrayList<>();
modules.add(new LogModule(reactApplicationContext));
return modules;
@Override
public List<Class<? extends JavaScriptModule>> createJSModules()
return Collections.emptyList();
@Override
public List<ViewManager> createViewManagers(ReactApplicationContext reactApplicationContext)
return Collections.emptyList();
很简单，装到自定义的List中。
第四步
CatalystInstanceImpl catalystInstance;
try
catalystInstance = catalystInstanceBuilder.build();
finally
Systrace.endSection(0L);
ReactMarker.logMarker("CREATE_CATALYST_INSTANCE_END");
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；
在这里ReactBridge由CatalystInstance的Constructor创建。看下它的构造函数：
private CatalystInstanceImpl(ReactQueueConfigurationSpec ReactQueueConfigurationSpec, final JavaScriptExecutor jsExecutor, NativeModuleRegistry registry, final JavaScriptModulesConfig jsModulesConfig, JSBundleLoader jsBundleLoader, NativeModuleCallExceptionHandler nativeModuleCallExceptionHandler)
this.mPendingJSCalls = new AtomicInteger(0);
this.mJsPendingCallsTitleForTrace = "pending_js_calls_instance" + sNextInstanceIdForTrace.getAndIncrement();
this.mDestroyed = false;
this.mJSToJavaCallsTeardownLock = new Object();
this.mJavaToJSCallsTeardownLock = new Object();
this.mInitialized = false;
FLog.d("React", "Initializing React Bridge.");
this.mReactQueueConfiguration = ReactQueueConfigurationImpl.create(ReactQueueConfigurationSpec, new CatalystInstanceImpl.NativeExceptionHandler(null));
this.mBridgeIdleListeners = new CopyOnWriteArrayList();
this.mJavaRegistry = registry;
this.mJSModuleRegistry = new JavaScriptModuleRegistry(this, jsModulesConfig);
this.mJSBundleLoader = jsBundleLoader;
this.mNativeModuleCallExceptionHandler = nativeModuleCallExceptionHandler;
this.mTraceListener = new CatalystInstanceImpl.JSProfilerTraceListener(null);
try
this.mBridge = (ReactBridge)this.mReactQueueConfiguration.getJSQueueThread().callOnQueue(new Callable()
public ReactBridge call() throws Exception
Systrace.beginSection(0L, "initializeBridge");
ReactBridge var1;
try
var1 = CatalystInstanceImpl.this.initializeBridge(jsExecutor, jsModulesConfig);
finally
Systrace.endSection(0L);
return var1;
).get();
catch (Exception var8)
throw new RuntimeException("Failed to initialize bridge", var8);
注意到这行代码：
this.mJSModuleRegistry = new JavaScriptModuleRegistry(this, jsModulesConfig);这里通过jsModulesConfig（封装了module）创建了JSModuleRegistry。好了js注册表终于创建成功了。这里有两个问题，native注册表在哪创建呢，还有就是注册表什么时候传给js层呢。先留着这两个问题。
接下来看下initializeBridge方法：
private ReactBridge initializeBridge (JavaScriptExecutor jsExecutor, JavaScriptModulesConfig jsModulesConfig)
this .mReactQueueConfiguration.getJSQueueThread().assertIsOnThread() ;
Assertions.assertCondition( this.mBridge == null, "initializeBridge should be called once" );
Systrace.beginSection( 0L, "ReactBridgeCtor" );
ReactBridge bridge ;
try
bridge = new ReactBridge(jsExecutor, new CatalystInstanceImpl.NativeModulesReactCallback( null), this.mReactQueueConfiguration.getNativeModulesQueueThread()) ;
this.mMainExecutorToken = bridge.getMainExecutorToken() ;
finally
Systrace.endSection(0L );
Systrace.beginSection(0L , "setBatchedBridgeConfig");
try
bridge.setGlobalVariable("__fbBatchedBridgeConfig" , this.buildModulesConfigJSONProperty( this.mJavaRegistry, jsModulesConfig));
bridge.setGlobalVariable( "__RCTProfileIsProfiling" , Systrace.isTracing( 0L)?"true" :"false") ;
finally
Systrace.endSection(0L );
this .mJavaRegistry.notifyReactBridgeInitialized(bridge) ;
return bridge ;
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。bridge.setGlobalVariable是一个native函数。让我们猜一下下它的功能，就是用jsModulesConfig这个参数在js层中生成模块注册表，先看一下参数 buildModulesConfigJSONProperty的代码：
private String buildModulesConfigJSONProperty(NativeModuleRegistry nativeModuleRegistry, JavaScriptModulesConfig jsModulesConfig)
StringWriter stringWriter = new StringWriter();
JsonWriter writer = new JsonWriter(stringWriter);
String ioe;
try
writer.beginObject();
writer.name("remoteModuleConfig");
nativeModuleRegistry.writeModuleDescriptions(writer);
writer.name("localModulesConfig");
jsModulesConfig.writeModuleDescriptions(writer);
writer.endObject();
ioe = stringWriter.toString();
catch (IOException var14)
throw new RuntimeException("Unable to serialize JavaScript module declaration", var14);
finally
try
writer.close();
catch (IOException var13)
;
return ioe;
看到JsonWriter就知道是把NativeModuleRegistry 和JavaScriptModulesConfig 转换成Json字符串，其中remoteModuleConfig指NativeModuleRegistry 信息，localModulesConfig指JavaScriptModulesConfig 信息。看下JavaScriptModulesConfig 的writeModuleDescriptions方法：
public void writeModuleDescriptions(JsonWriter writer) throws IOException
writer.beginObject();
Iterator i$ = this.mModules.iterator();
while(i$.hasNext())
JavaScriptModuleRegistration registration = (JavaScriptModuleRegistration)i$.next();
writer.name(registration.getName()).beginObject();
this.appendJSModuleToJSONObject(writer, registration);
writer.endObject();
writer.endObject();
看下appendJSModuleToJSONObject方法：
private void appendJSModuleToJSONObject(JsonWriter writer, JavaScriptModuleRegistration registration) throws IOException
writer.name("moduleID").value((long)registration.getModuleId());
writer.name("methods").beginObject();
Iterator i$ = registration.getMethods().iterator();
while(i$.hasNext())
Method method = (Method)i$.next();
writer.name(method.getName()).beginObject();
writer.name("methodID").value((long)registration.getMethodId(method));
writer.endObject();
writer.endObject();
if(registration.getModuleInterface().isAnnotationPresent(SupportsWebWorkers.class))
writer.name("supportsWebWorkers").value(true);
从上代码可知生成的json字符串包含moduleID和methodID信息。NativeModuleRegistry 也同理，我们大概看下它的代码：
void writeModuleDescriptions(JsonWriter writer) throws IOException
Systrace.beginSection(0L, "CreateJSON");
try
writer.beginObject();
Iterator i$ = this.mModuleTable.iterator();
while(i$.hasNext())
NativeModuleRegistry.ModuleDefinition moduleDef = (NativeModuleRegistry.ModuleDefinition)i$.next();
writer.name(moduleDef.name).beginObject();
writer.name("moduleID").value((long)moduleDef.id);
writer.name("supportsWebWorkers").value(moduleDef.target.supportsWebWorkers());
writer.name("methods").beginObject();
for(int i = 0; i < moduleDef.methods.size(); ++i)
NativeModuleRegistry.MethodRegistration method = (NativeModuleRegistry.MethodRegistration)moduleDef.methods.get(i);
writer.name(method.name).beginObject();
writer.name("methodID").value((long)i);
writer.name("type").value(method.method.getType());
writer.endObject();
writer.endObject();
moduleDef.target.writeConstantsField(writer, "constants");
writer.endObject();
writer.endObject();
finally
Systrace.endSection(0L);
接下来我们要找到setGlobalVariable的Native层代码，C++层代码我不太懂，这里参考了下别人的分析过程。大概过程是这样，首先入口是OnLoad.cpp。在其中找到如下代码：
void Bridge::setGlobalVariable(const std::string& propName, const std::string& jsonValue)
runOnExecutorQueue(*m_mainExecutorToken, [=] (JSExecutor* executor)
executor->setGlobalVariable(propName, jsonValue);
);
都是塞进runOnExecutorQueue执行队列里面等待调用，最后回调到JSExecutor，而JSExecutor的实现类是JSCExecutor，最后来看看它的setGlobalVariable方法。
void JSCExecutor::setGlobalVariable(const std::string& propName, const std::string& jsonValue)
auto globalObject = JSContextGetGlobalObject(m_context);
String jsPropertyName(propName.c_str());
String jsValueJSON(jsonValue.c_str());
auto valueToInject = JSValueMakeFromJSONString(m_context, jsValueJSON);
JSObjectSetProperty(m_context, globalObject, jsPropertyName, valueToInject, 0, NULL);
懂个大概吧，参数propName是从Java层传递过来的，相当于java代码中的__fbBatchedBridgeConfig和__RCTProfileIsProfiling。jsPropertyName方法就是buildModulesConfigJSONProperty封装好的对象。JSContextGetGlobalObject是WeiKit的方法，接下来会调用到js层的MessageQueue中：
const MessageQueue = require('MessageQueue');
const BatchedBridge = new MessageQueue(
__fbBatchedBridgeConfig.remoteModuleConfig,
__fbBatchedBridgeConfig.localModulesConfig,
);生成两个映射表，从上面的代码我们己经分析过了，remoteModuleConfig是NativeModuleRegisty映射表内容。localModulesConfig则是JavaScriptModule内容。
到这里，js就生成了两张映射表了，这样java层和js层就都存在同样的映射表，相互通信就是通过它来实现。扯远了，回到createReactView。
第五步
try
catalystInstance.runJSBundle();
finally
Systrace.endSection(0L);
ReactMarker.logMarker("RUN_JS_BUNDLE_END");
调用catalystInstance.runJSBundle加载解析Jsbundle。
回到createReactView方法，看catalystInstance.runJSBundle：
public void runJSBundle()
try
this.mJSBundleHasLoaded = ((Boolean)this.mReactQueueConfiguration.getJSQueueThread().callOnQueue(new Callable()
public Boolean call() throws Exception
Assertions.assertCondition(!CatalystInstanceImpl.this.mJSBundleHasLoaded, "JS bundle was already loaded!");
CatalystInstanceImpl.this.incrementPendingJSCalls();
Systrace.beginSection(0L, "loadJSScript");
try
CatalystInstanceImpl.this.mJSBundleLoader.loadScript(CatalystInstanceImpl.this.mBridge);
Systrace.registerListener(CatalystInstanceImpl.this.mTraceListener);
catch (JSExecutionException var5)
CatalystInstanceImpl.this.mNativeModuleCallExceptionHandler.handleException(var5);
finally
Systrace.endSection(0L);
return Boolean.valueOf(true);
).get()).booleanValue();
catch (Exception var2)
throw new RuntimeException(var2);
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。
在创建完React Context后会执行ReactContextInitAsyncTask的onPostExecute。来看下onPostExecute的代码：
private void setupReactContext(ReactApplicationContext reactContext)
UiThreadUtil.assertOnUiThread();
Assertions.assertCondition(this.mCurrentReactContext == null);
this.mCurrentReactContext = (ReactContext)Assertions.assertNotNull(reactContext);
CatalystInstance catalystInstance = (CatalystInstance)Assertions.assertNotNull(reactContext.getCatalystInstance());
catalystInstance.initialize();
this.mDevSupportManager.onNewReactContextCreated(reactContext);
this.mMemoryPressureRouter.addMemoryPressureListener(catalystInstance);
this.moveReactContextToCurrentLifecycleState();
Iterator listeners = this.mAttachedRootViews.iterator();
while(listeners.hasNext())
ReactRootView arr$ = (ReactRootView)listeners.next();
this.attachMeasuredRootViewToInstance(arr$, catalystInstance);
ReactInstanceEventListener[] var8 = new ReactInstanceEventListener[this.mReactInstanceEventListeners.size()];
var8 = (ReactInstanceEventListener[])this.mReactInstanceEventListeners.toArray(var8);
ReactInstanceEventListener[] var9 = var8;
int len$ = var8.length;
for(int i$ = 0; i$ < len$; ++i$)
ReactInstanceEventListener listener = var9[i$];
listener.onReactContextInitialized(reactContext);
这里主要实现两个功能，第一，调用catalystInstance.initialize()来创建NativeModuleRegistry,好啦，回答了一个问题了哈。
public void<以上是关于React Native之底层源码分析篇的主要内容，如果未能解决你的问题，请参考以下文章
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