ReactNative的启动流程精讲(基于ReactNative
2020-04-15 本文已影响0人
Frewen_Wong
title: ReactNative的启动流程精讲(基于ReactNative0.61.5)
date: 2020-03-13 21:00:02
tags: ReactNative；Android；
ReactNative的启动流程精讲(基于ReactNative0.61.5)
文章参考：https://www.jianshu.com/p/baff68f85d41
创建ReactNativeHost
ReactNative的启动流程，我们首先看Application中的代码，实例化ReactNativeHost。ReactNativeHost主要的工作就是创建了ReactInstanceManager，它将一些信息传递给了ReactInstanceManager。同时，我们看一下ReactNativeHost的提供的方法。
public abstract class ReactNativeHost {
protected ReactInstanceManager createReactInstanceManager() {
ReactInstanceManagerBuilder builder = ReactInstanceManager.builder()
//应用上下文
.setApplication(mApplication)
//JSMainModuleP相当于应用首页的js Bundle，可以传递url从服务器拉取js Bundle
//当然这个只在dev模式下可以使用
.setJSMainModulePath(getJSMainModuleName())
//是否开启dev模式
.setUseDeveloperSupport(getUseDeveloperSupport())
//红盒的回调
.setRedBoxHandler(getRedBoxHandler())
//自定义UI实现机制，这个我们一般用不到
.setUIImplementationProvider(getUIImplementationProvider())
.setInitialLifecycleState(LifecycleState.BEFORE_CREATE);
//添加ReactPackage
for (ReactPackage reactPackage : getPackages()) {
builder.addPackage(reactPackage);
}
//获取js Bundle的加载路径
String jsBundleFile = getJSBundleFile();
if (jsBundleFile != null) {
builder.setJSBundleFile(jsBundleFile);
} else {
builder.setBundleAssetName(Assertions.assertNotNull(getBundleAssetName()));
}
return builder.build();
}
}
下面是ReactNativeHost提供的一些方法：
protected @Nullable RedBoxHandler getRedBoxHandler();
protected @Nullable JavaScriptExecutorFactory getJavaScriptExecutorFactory();
protected final Application getApplication();
protected UIImplementationProvider getUIImplementationProvider();
实例化ReactActivityDelegate：
启动ReactActivity的子类实例，在这个Activty的启动流程中，正式开始我们ReactNative启动和加载流程。
我们先来分析一下ReactActivityDelegate。我么可以看到ReactActivityDelegate的一些提供的方法。就知道这个类的一些职责。他主要就是Activity的宿主的一些生命周期的委托调用。也就是所有ReactNative和宿主Activity的关联都是通过这个类类简历联系的。
当然我们也看到。其实所有的生命周期的方法。这个类要么委托给ReactDelegate。要么就是直接ReactInstanceManager进行处理。所以这个类的职责也是非常简单的。
可以说ReactNative和她的宿主Activity达到了很好的解耦。
public abstract class ReactActivity extends AppCompatActivity
implements DefaultHardwareBackBtnHandler, PermissionAwareActivity {
private final ReactActivityDelegate mDelegate;
protected ReactActivity() {
mDelegate = createReactActivityDelegate();
}
/**
* Returns the name of the main component registered from JavaScript. This is used to schedule
* rendering of the component. e.g. "MoviesApp"
*/
protected @Nullable String getMainComponentName() {
return null;
}
/** Called at construction time, override if you have a custom delegate implementation. */
protected ReactActivityDelegate createReactActivityDelegate() {
return new ReactActivityDelegate(this, getMainComponentName());
}
.......
}
这个类很简单，就是实例化的一个Activity的委托对象。然后所有的生命周期调用全部使用ReactActivityDelegate的代理对象完成。
那么下面，我们看一下这个类的实现。
public ReactActivityDelegate(ReactActivity activity, @Nullable String mainComponentName) {
Log.d(TAG, "第二步：FMsg: 实例化ReactActivityDelegate called with: activity = [" + activity + "], mainComponentName = [" + mainComponentName + "]");
mActivity = activity;
mMainComponentName = mainComponentName;
}
我们看一下。Activity的onCreate的方法的代理实现。
实例化ReactDelegate
protected void onCreate(Bundle savedInstanceState) {
String mainComponentName = getMainComponentName();
mReactDelegate =
new ReactDelegate(
getPlainActivity(), getReactNativeHost(), mainComponentName, getLaunchOptions()) {
@Override
protected ReactRootView createRootView() {
return ReactActivityDelegate.this.createRootView();
}
};
//mMainComponentName就是上面ReactActivity.getMainComponentName()返回的组件名
if (mMainComponentName != null) {
//载入app页面
loadApp(mainComponentName);
}
}
这个方法一个，实例化ReactDelegate对象。二是调用loadApp的方法。
我们来看一下ReactDelegate的这个对象。他的职责到底是什么呢？？
protected void loadApp(String appKey) {
mReactDelegate.loadApp(appKey);
getPlainActivity().setContentView(mReactDelegate.getReactRootView());
}
这个方法很简单。还是调用了ReactDelegate的loadApp方法。至此位置ReactActivityDelegate的启动流程中的职责也就告一段落。下面我们看一下ReactDelegate里面的loadApp
public void loadApp(String appKey) {
if (mReactRootView != null) {
throw new IllegalStateException("Cannot loadApp while app is already running.");
}
//创建ReactRootView作为根视图,它本质上是一个FrameLayout
mReactRootView = createRootView();、
//启动RN应用.这个地方我们要注意下。ReactInstanceManager就是从这个地方开始实例化的。
mReactRootView.startReactApplication(
getReactNativeHost().getReactInstanceManager(), appKey, mLaunchOptions);
}
最终这个方法是调用到ReactRootView。这个View我们知道，其实就是我们通过setContentView设置给Activity宿主的FameLayout
实例化ReactInstanceManager
我们可以从代码中看到，在startReactApplication的时候，我们通过ReactNativeHost的实例化对象来获取ReactInstanceManager
/** Get the current {@link ReactInstanceManager} instance, or create one. */
public ReactInstanceManager getReactInstanceManager() {
if (mReactInstanceManager == null) {
ReactMarker.logMarker(ReactMarkerConstants.GET_REACT_INSTANCE_MANAGER_START);
mReactInstanceManager = createReactInstanceManager();
ReactMarker.logMarker(ReactMarkerConstants.GET_REACT_INSTANCE_MANAGER_END);
}
return mReactInstanceManager;
}
protected ReactInstanceManager createReactInstanceManager() {
ReactMarker.logMarker(ReactMarkerConstants.BUILD_REACT_INSTANCE_MANAGER_START);
Log.d(TAG, "FMsg:第五步：createReactInstanceManager() called");
ReactInstanceManagerBuilder builder =
ReactInstanceManager.builder()
.setApplication(mApplication)
// 设置JSMain的根路径地址。也就是index.js //"index.android"
.setJSMainModulePath(getJSMainModuleName())
.setUseDeveloperSupport(getUseDeveloperSupport())
//红盒的回调
.setRedBoxHandler(getRedBoxHandler())
// 获取JS执行引擎的工作累的方法。默认是JSC。当然我们也可以自定义设置成V8的引擎
// 如果需要自定义设置，那么Application中重写这个方法
.setJavaScriptExecutorFactory(getJavaScriptExecutorFactory())
//自定义UI实现机制，这个我们一般用不到
.setUIImplementationProvider(getUIImplementationProvider())
.setJSIModulesPackage(getJSIModulePackage())
.setInitialLifecycleState(LifecycleState.BEFORE_CREATE);
// 类实例化的作用就是传递给ReactInstanceManager所有的Packages
Log.i(TAG, "FMsg:第五步：createReactInstanceManager: addPackage size = " + getPackages().size());
// 这个使我们Application实例化的时候，我们提供的ReactPackage
for (ReactPackage reactPackage : getPackages()) {
builder.addPackage(reactPackage);
}
String jsBundleFile = getJSBundleFile();
Log.i(TAG, "FMsg:第五步：createReactInstanceManager: jsBundleFile = "+jsBundleFile);
if (jsBundleFile != null) {
builder.setJSBundleFile(jsBundleFile);
} else {
builder.setBundleAssetName(Assertions.assertNotNull(getBundleAssetName()));
}
// 这个建造者模式，可以好好分析一下。里面有很多的默认参数
ReactInstanceManager reactInstanceManager = builder.build();
ReactMarker.logMarker(ReactMarkerConstants.BUILD_REACT_INSTANCE_MANAGER_END);
return reactInstanceManager;
}
其实从这个地方。ReactNativeHost的历史使命就完成了。所有我们复写的他的提供方法都是在这个地方传递给ReactInstance的构造化实例对象。
下面，我们来看一下ReactInstanceManager的构造函数
/* package */ ReactInstanceManager(
Context applicationContext,
@Nullable Activity currentActivity,
@Nullable DefaultHardwareBackBtnHandler defaultHardwareBackBtnHandler,
JavaScriptExecutorFactory javaScriptExecutorFactory,
@Nullable JSBundleLoader bundleLoader,
@Nullable String jsMainModulePath,
List<ReactPackage> packages,
boolean useDeveloperSupport,
@Nullable NotThreadSafeBridgeIdleDebugListener bridgeIdleDebugListener,
LifecycleState initialLifecycleState,
@Nullable UIImplementationProvider mUIImplementationProvider,
NativeModuleCallExceptionHandler nativeModuleCallExceptionHandler,
@Nullable RedBoxHandler redBoxHandler,
boolean lazyViewManagersEnabled,
@Nullable DevBundleDownloadListener devBundleDownloadListener,
int minNumShakes,
// 这个参数也比较重要，这个参数就是ReactNative的刷新帧的频率。默认-1.表示直接使用Android的刷新帧频率
int minTimeLeftInFrameForNonBatchedOperationMs,
@Nullable JSIModulePackage jsiModulePackage,
@Nullable Map<String, RequestHandler> customPackagerCommandHandlers) {
Log.d(ReactConstants.TAG, "ReactInstanceManager.ctor()");
Log.d(TAG, "FMsg:第五步：ReactInstanceManager() called with: currentActivity = [" + currentActivity + "], defaultHardwareBackBtnHandler = [" + defaultHardwareBackBtnHandler + "], javaScriptExecutorFactory = [" + javaScriptExecutorFactory + "], bundleLoader = [" + bundleLoader + "], jsMainModulePath = [" + jsMainModulePath + "], packages = [" + packages + "], useDeveloperSupport = [" + useDeveloperSupport + "], bridgeIdleDebugListener = [" + bridgeIdleDebugListener + "], initialLifecycleState = [" + initialLifecycleState + "], mUIImplementationProvider = [" + mUIImplementationProvider + "], nativeModuleCallExceptionHandler = [" + nativeModuleCallExceptionHandler + "], redBoxHandler = [" + redBoxHandler + "], lazyViewManagersEnabled = [" + lazyViewManagersEnabled + "], devBundleDownloadListener = [" + devBundleDownloadListener + "], minNumShakes = [" + minNumShakes + "], minTimeLeftInFrameForNonBatchedOperationMs = [" + minTimeLeftInFrameForNonBatchedOperationMs + "], jsiModulePackage = [" + jsiModulePackage + "], customPackagerCommandHandlers = [" + customPackagerCommandHandlers + "]");
initializeSoLoaderIfNecessary(applicationContext);
DisplayMetricsHolder.initDisplayMetricsIfNotInitialized(applicationContext);
mApplicationContext = applicationContext;
mCurrentActivity = currentActivity;
mDefaultBackButtonImpl = defaultHardwareBackBtnHandler;
// 其实默认传入的null 如果我们想使用其他JS引擎，比如V8.我们可以在这里面进行传入
mJavaScriptExecutorFactory = javaScriptExecutorFactory;
mBundleLoader = bundleLoader;
mJSMainModulePath = jsMainModulePath;
mPackages = new ArrayList<>();
mUseDeveloperSupport = useDeveloperSupport;
Systrace.beginSection(
Systrace.TRACE_TAG_REACT_JAVA_BRIDGE, "ReactInstanceManager.initDevSupportManager");
mDevSupportManager =
DevSupportManagerFactory.create(
applicationContext,
createDevHelperInterface(),
mJSMainModulePath,
useDeveloperSupport,
redBoxHandler,
devBundleDownloadListener,
minNumShakes,
customPackagerCommandHandlers);
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
mBridgeIdleDebugListener = bridgeIdleDebugListener;
mLifecycleState = initialLifecycleState;
mMemoryPressureRouter = new MemoryPressureRouter(applicationContext);
mNativeModuleCallExceptionHandler = nativeModuleCallExceptionHandler;
/// 这个地方就是添加ReactPackage
synchronized (mPackages) {
PrinterHolder.getPrinter()
.logMessage(ReactDebugOverlayTags.RN_CORE, "RNCore: Use Split Packages");
// 这个方法很重要，这个方法我们会将系统内置的那些CoreModulesPackage添加进去
// AndroidInfoModule.class,
// DeviceEventManagerModule.class,
// DeviceInfoModule.class,
// DevSettingsModule.class,
// ExceptionsManagerModule.class,
// HeadlessJsTaskSupportModule.class,
// SourceCodeModule.class,
// Timing.class,
// UIManagerModule.class
mPackages.add(
new CoreModulesPackage(
this,
new DefaultHardwareBackBtnHandler() {
@Override
public void invokeDefaultOnBackPressed() {
ReactInstanceManager.this.invokeDefaultOnBackPressed();
}
},
mUIImplementationProvider,
lazyViewManagersEnabled,
minTimeLeftInFrameForNonBatchedOperationMs));
if (mUseDeveloperSupport) {
mPackages.add(new DebugCorePackage());
}
mPackages.addAll(packages);
}
mJSIModulePackage = jsiModulePackage;
// Instantiate ReactChoreographer in UI thread.
// 这个就是实例化Android的序列帧的监听对象
ReactChoreographer.initialize();
if (mUseDeveloperSupport) {
mDevSupportManager.startInspector();
}
}
从ReactInstanceManager的构造函数，我们可以看到。所有ReactNative的启动的初始化资源基本都已经准备完毕。所以startReactApplication的方法。我们必须要传入ReactInstanceManager实例化对象。
其实通过查看ReactInstance的类的内容，我们可以看到这个类的方法其实也是比较简单的。他的关于启动流程最大的一个作用就是创建ReactContext。那么这个创建ReactContext是什么开始的呢？
我们来继续看ReactRootView的startReactApplication方法。
startReactApplication
@ThreadConfined(UI)
public void startReactApplication(
ReactInstanceManager reactInstanceManager,
String moduleName,
@Nullable Bundle initialProperties,
@Nullable String initialUITemplate) {
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "startReactApplication");
try {
// 线程检查
UiThreadUtil.assertOnUiThread();
// TODO(6788889): Use POJO instead of bundle here, apparently we can't just use WritableMap
// here as it may be deallocated in native after passing via JNI bridge, but we want to reuse
// it in the case of re-creating the catalyst instance
Assertions.assertCondition(
mReactInstanceManager == null,
"This root view has already been attached to a catalyst instance manager");
mReactInstanceManager = reactInstanceManager;
mJSModuleName = moduleName;
mAppProperties = initialProperties;
mInitialUITemplate = initialUITemplate;
if (mUseSurface) {
// TODO initialize surface here
}
//创建RN上下文上下文对象
mReactInstanceManager.createReactContextInBackground();
//attachToReactInstanceManager 调用的是mReactInstanceManager.attachRootView(this)
attachToReactInstanceManager();
} finally {
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
}
}
这个方法比较深，我们可以一步步往下看。进入到这个方法，就进入到ReactInstance的核心功能。也是ReactNative启动的核心流程。也是最重要的流程中。createReactContext的创建流程。
@ThreadConfined(UI)
public void createReactContextInBackground() {
Log.d(ReactConstants.TAG, "ReactInstanceManager.createReactContextInBackground()");
Log.d(TAG, "FMsg:第六步：ReactRootView开始创建ReactContext createReactContextInBackground() called");
UiThreadUtil
.assertOnUiThread(); // Assert before setting mHasStartedCreatingInitialContext = true
if (!mHasStartedCreatingInitialContext) {
mHasStartedCreatingInitialContext = true;
recreateReactContextInBackgroundInner();
}
}
@ThreadConfined(UI)
private void recreateReactContextInBackgroundInner() {
Log.d(ReactConstants.TAG, "ReactInstanceManager.recreateReactContextInBackgroundInner()");
Log.d(TAG, "FMsg:第六步：调用内部方法recreateReactContextInBackgroundInner() called");
PrinterHolder.getPrinter()
.logMessage(ReactDebugOverlayTags.RN_CORE, "RNCore: recreateReactContextInBackground");
UiThreadUtil.assertOnUiThread();
// 调试相关的逻辑，咱们暂时忽略
if (mUseDeveloperSupport && mJSMainModulePath != null) {
final DeveloperSettings devSettings = mDevSupportManager.getDevSettings();
if (!Systrace.isTracing(TRACE_TAG_REACT_APPS | TRACE_TAG_REACT_JS_VM_CALLS)) {
if (mBundleLoader == null) {
mDevSupportManager.handleReloadJS();
} else {
mDevSupportManager.isPackagerRunning(
new PackagerStatusCallback() {
@Override
public void onPackagerStatusFetched(final boolean packagerIsRunning) {
UiThreadUtil.runOnUiThread(
new Runnable() {
@Override
public void run() {
if (packagerIsRunning) {
mDevSupportManager.handleReloadJS();
} else if (mDevSupportManager.hasUpToDateJSBundleInCache()
&& !devSettings.isRemoteJSDebugEnabled()) {
// If there is a up-to-date bundle downloaded from server,
// with remote JS debugging disabled, always use that.
onJSBundleLoadedFromServer(null);
} else {
// If dev server is down, disable the remote JS debugging.
devSettings.setRemoteJSDebugEnabled(false);
recreateReactContextInBackgroundFromBundleLoader();
}
}
});
}
});
}
return;
}
}
recreateReactContextInBackgroundFromBundleLoader();
}
@ThreadConfined(UI)
private void recreateReactContextInBackgroundFromBundleLoader() {
Log.d(
ReactConstants.TAG,
"ReactInstanceManager.recreateReactContextInBackgroundFromBundleLoader()");
Log.d(TAG, "FMsg:第六步：线上环境来将会使用后台任务创建ReactContext recreateReactContextInBackgroundFromBundleLoader() called");
PrinterHolder.getPrinter()
.logMessage(ReactDebugOverlayTags.RN_CORE, "RNCore: load from BundleLoader");
recreateReactContextInBackground(mJavaScriptExecutorFactory, mBundleLoader);
}
@ThreadConfined(UI)
private void runCreateReactContextOnNewThread(final ReactContextInitParams initParams) {
Log.d(ReactConstants.TAG, "ReactInstanceManager.runCreateReactContextOnNewThread()");
Log.d(TAG, "FMsg:第六步：runCreateReactContextOnNewThread() called with: initParams = [" + initParams + "]");
UiThreadUtil.assertOnUiThread();
synchronized (mAttachedReactRoots) {
synchronized (mReactContextLock) {
// 生命周期的回收，主要是针对可能会造成的多次初始化RN环境的
if (mCurrentReactContext != null) {
tearDownReactContext(mCurrentReactContext);
mCurrentReactContext = null;
}
}
}
mCreateReactContextThread =
new Thread(
null,
new Runnable() {
@Override
public void run() {
ReactMarker.logMarker(REACT_CONTEXT_THREAD_END);
synchronized (ReactInstanceManager.this.mHasStartedDestroying) {
while (ReactInstanceManager.this.mHasStartedDestroying) {
try {
ReactInstanceManager.this.mHasStartedDestroying.wait();
} catch (InterruptedException e) {
continue;
}
}
}
// As destroy() may have run and set this to false, ensure that it is true before we
// create
mHasStartedCreatingInitialContext = true;
try {
Process.setThreadPriority(Process.THREAD_PRIORITY_DISPLAY);
ReactMarker.logMarker(VM_INIT);
Log.i(TAG, "FMsg:第六步：runCreateReactContextOnNewThread run: " + Thread.currentThread().getName());
final ReactApplicationContext reactApplicationContext =
createReactContext(
initParams.getJsExecutorFactory().create(),
initParams.getJsBundleLoader());
mCreateReactContextThread = null;
ReactMarker.logMarker(PRE_SETUP_REACT_CONTEXT_START);
// 这个地方也是一个保护机制，我们暂时不需要关注
final Runnable maybeRecreateReactContextRunnable =
new Runnable() {
@Override
public void run() {
if (mPendingReactContextInitParams != null) {
runCreateReactContextOnNewThread(mPendingReactContextInitParams);
mPendingReactContextInitParams = null;
}
}
};
Runnable setupReactContextRunnable =
new Runnable() {
@Override
public void run() {
try {
setupReactContext(reactApplicationContext);
} catch (Exception e) {
mDevSupportManager.handleException(e);
}
}
};
reactApplicationContext.runOnNativeModulesQueueThread(setupReactContextRunnable);
UiThreadUtil.runOnUiThread(maybeRecreateReactContextRunnable);
} catch (Exception e) {
mDevSupportManager.handleException(e);
}
}
},
"create_react_context");
ReactMarker.logMarker(REACT_CONTEXT_THREAD_START);
mCreateReactContextThread.start();
}
这个地方就是我们比较重要的创建ReactContext对象的逻辑。
/** @return instance of {@link ReactContext} configured a {@link CatalystInstance} set */
private ReactApplicationContext createReactContext(
JavaScriptExecutor jsExecutor, JSBundleLoader jsBundleLoader) {
Log.d(TAG, "FMsg:第六步：ReactInstanceManager.createReactContext " + Thread.currentThread().getName());
Log.d(TAG, "FMsg:第六步：createReactContext() called with: jsExecutor = [" + jsExecutor + "], jsBundleLoader = [" + jsBundleLoader + "]");
ReactMarker.logMarker(CREATE_REACT_CONTEXT_START, jsExecutor.getName());
// 这个地方就进行了实例化reactContext
// ReactApplicationContext extends ReactContext extends ContextWrapper
// 构造函数传入的是Context。 eactApplicationContext是ReactContext的包装类。
final ReactApplicationContext reactContext = new ReactApplicationContext(mApplicationContext);
// 这个就是NativeModuleCallExceptionHandler.异常捕获器
NativeModuleCallExceptionHandler exceptionHandler =
mNativeModuleCallExceptionHandler != null
? mNativeModuleCallExceptionHandler
: mDevSupportManager;
reactContext.setNativeModuleCallExceptionHandler(exceptionHandler);
// 创建JavaModule注册表Builder，用来创建JavaModule注册表，JavaModule注册表将所有的JavaModule注册到CatalystInstance中。
NativeModuleRegistry nativeModuleRegistry = processPackages(reactContext, mPackages, false);
// 最最重要的一个对象，催化器实例对象
// jsExecutor、nativeModuleRegistry、nativeModuleRegistry等各种参数处理好之后，开始构建CatalystInstanceImpl实例。
CatalystInstanceImpl.Builder catalystInstanceBuilder =
new CatalystInstanceImpl.Builder()
// 设置ReactNative的消息队列的配置数据
.setReactQueueConfigurationSpec(ReactQueueConfigurationSpec.createDefault())
// 通过JS执行器工厂实例化的JS线程执行器
.setJSExecutor(jsExecutor)
.setRegistry(nativeModuleRegistry)
.setJSBundleLoader(jsBundleLoader)
.setNativeModuleCallExceptionHandler(exceptionHandler);
ReactMarker.logMarker(CREATE_CATALYST_INSTANCE_START);
// CREATE_CATALYST_INSTANCE_END is in JSCExecutor.cpp
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "createCatalystInstance");
final CatalystInstance catalystInstance;
try {
// 没什么好说的。空值判断。但是催化器的构造函数我们需要研究一下。
// 里面针对消息队列的线程进行初始化
catalystInstance = catalystInstanceBuilder.build();
} finally {
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
ReactMarker.logMarker(CREATE_CATALYST_INSTANCE_END);
}
// 关联ReacContext与CatalystInstance实例化
// 解析上面实例化的是三个线程封装对象
reactContext.initializeWithInstance(catalystInstance);
if (mJSIModulePackage != null) {
// 这个默认是为null的。这个数据最初是在ReactNativeHost里面传入的
catalystInstance.addJSIModules(
mJSIModulePackage.getJSIModules(
reactContext, catalystInstance.getJavaScriptContextHolder()));
// 这个地方没太看懂
if (ReactFeatureFlags.useTurboModules) {
catalystInstance.setTurboModuleManager(
catalystInstance.getJSIModule(JSIModuleType.TurboModuleManager));
}
}
if (mBridgeIdleDebugListener != null) {
catalystInstance.addBridgeIdleDebugListener(mBridgeIdleDebugListener);
}
if (Systrace.isTracing(TRACE_TAG_REACT_APPS | TRACE_TAG_REACT_JS_VM_CALLS)) {
catalystInstance.setGlobalVariable("__RCTProfileIsProfiling", "true");
}
ReactMarker.logMarker(ReactMarkerConstants.PRE_RUN_JS_BUNDLE_START);
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "runJSBundle");
// 加载JSBundle的数据
catalystInstance.runJSBundle();
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
return reactContext;
}
这个是非常重要的方法，我们需要一点点来分析一下。
1、首先他将Application的对象用ReactApplicationContext进行包装，生成ReactApplication对象。这个没什么好说的。简单的包装而已。
2、创建JavaModule的注册表
3、进行CatalystInstanceImpl实例化
4、关联ReacContext与CatalystInstance实例化 解析上面实例化的是三个线程封装对象。这个地方。
我们主要作用是让reactContext来持有catalystInstance对象 两个作用：1、获取这个实力上面传入ReactQueueConfigurationSpec实例，或者三个消息队列线程封装的对象 2、主要是通过催化器实例获取JSModule、NativeModule
其次，ReacContext还有就是一些生命周期的管理
实例化CatalystInstanceImpl
下面就是最重要的催化剂实例的构造方法
private CatalystInstanceImpl(
final ReactQueueConfigurationSpec reactQueueConfigurationSpec,
final JavaScriptExecutor jsExecutor,
final NativeModuleRegistry nativeModuleRegistry,
final JSBundleLoader jsBundleLoader,
NativeModuleCallExceptionHandler nativeModuleCallExceptionHandler) {
Log.d(ReactConstants.TAG, "Initializing React Xplat Bridge.");
Log.d(TAG, "FMsg:第七步：CatalystInstanceImpl() called with: reactQueueConfigurationSpec = [" + reactQueueConfigurationSpec + "], jsExecutor = [" + jsExecutor + "], nativeModuleRegistry = [" + nativeModuleRegistry + "], jsBundleLoader = [" + jsBundleLoader + "], nativeModuleCallExceptionHandler = [" + nativeModuleCallExceptionHandler + "]");
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "createCatalystInstanceImpl");
// 重点关注一下这一方法。这是一个Native方法。这样我们就调用到Native层
mHybridData = initHybrid();
// ReactNative的消息队列相关的实例化
// TODO 这个地方要重点看一下
// 这个主要是分别在对应的线程中创建消息任务队列的Handler(搬运工)
// 当然还创建了两个线程(主线程不用创建)
mReactQueueConfiguration =
ReactQueueConfigurationImpl.create(
reactQueueConfigurationSpec, new NativeExceptionHandler());
mBridgeIdleListeners = new CopyOnWriteArrayList<>();
// NativeModules注入器
mNativeModuleRegistry = nativeModuleRegistry;
mJSModuleRegistry = new JavaScriptModuleRegistry();
// JSBundlerLoader
mJSBundleLoader = jsBundleLoader;
mNativeModuleCallExceptionHandler = nativeModuleCallExceptionHandler;
mNativeModulesQueueThread = mReactQueueConfiguration.getNativeModulesQueueThread();
mTraceListener = new JSProfilerTraceListener(this);
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
Log.d(TAG, "FMsg: 第七步：CatalystInstanceImpl() called Initializing React Xplat Bridge before initializeBridge");
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "initializeCxxBridge");
Log.d(TAG, "FMsg:第七步：CatalystInstanceImpl() called with: initializeCxxBridge");
// TODO 这个地方要重点看一下. 又一个非常重要的方法。
// 初始化Java和Native之间的Bridge桥。这个是一个Native方法
initializeBridge(
//
new BridgeCallback(this),
// JSCore的JS引擎
jsExecutor,
// JS消息队列线程封装对象
mReactQueueConfiguration.getJSQueueThread(),
// Native消息队列线程封装对象
mNativeModulesQueueThread,
// 非C++的Modules就是JavaModule.也就是我们在Application里面封装的Modules
// 这些NativeModules都会被封装成JavaModuleWrapper对象送给Native层
mNativeModuleRegistry.getJavaModules(this),
// 获取我们所有的Module中的C++的modules。这个是通过注解来标记那个NativeModule是C++
// 但是我们翻了一下源码，没看到哪个NativeModule是C++
mNativeModuleRegistry.getCxxModules());
Log.d(ReactConstants.TAG, "第七步：实例化Initializing React Xplat Bridge after initializeBridge");
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
mJavaScriptContextHolder = new JavaScriptContextHolder(getJavaScriptContext());
}
下面，我们看一下Native层的调用
jni::local_ref<CatalystInstanceImpl::jhybriddata> CatalystInstanceImpl::initHybrid(
jni::alias_ref<jclass>) {
cout<<"===========FMsg:CatalystInstanceImpl initHybrid called==============="<<endl;
return makeCxxInstance();
}
void CatalystInstanceImpl::initializeBridge(
jni::alias_ref<ReactCallback::javaobject> callback,
// This executor is actually a factory holder.
JavaScriptExecutorHolder* jseh,
jni::alias_ref<JavaMessageQueueThread::javaobject> jsQueue,
jni::alias_ref<JavaMessageQueueThread::javaobject> nativeModulesQueue,
jni::alias_ref<jni::JCollection<JavaModuleWrapper::javaobject>::javaobject> javaModules,
jni::alias_ref<jni::JCollection<ModuleHolder::javaobject>::javaobject> cxxModules) {
LOG(INFO) <<"===========FMsg:CatalystInstanceImpl initializeBridge==============="<<endl;
// .............省略部分代码
moduleRegistry_ = std::make_shared<ModuleRegistry>(
buildNativeModuleList(
std::weak_ptr<Instance>(instance_),
javaModules,
cxxModules,
moduleMessageQueue_));
instance_->initializeBridge(
std::make_unique<JInstanceCallback>(
callback,
moduleMessageQueue_),
jseh->getExecutorFactory(),
folly::make_unique<JMessageQueueThread>(jsQueue),
moduleRegistry_);
}
至此，Java层的代码执行完毕。我们彻底就进入Native层的代码逻辑了。上面Jni代码中，调用的instance_->initializeBridge()。 这个逻辑层，我们要到Native层去查找逻辑实现了。
void Instance::initializeBridge(
std::unique_ptr<InstanceCallback> callback,
std::shared_ptr<JSExecutorFactory> jsef,
std::shared_ptr<MessageQueueThread> jsQueue,
std::shared_ptr<ModuleRegistry> moduleRegistry) {
LOG(INFO) <<"===========FMsg:Instance initializeBridge==============="<<endl;
callback_ = std::move(callback);
moduleRegistry_ = std::move(moduleRegistry);
jsQueue->runOnQueueSync([this, &jsef, jsQueue]() mutable {
nativeToJsBridge_ = folly::make_unique<NativeToJsBridge>(
jsef.get(), moduleRegistry_, jsQueue, callback_);
std::lock_guard<std::mutex> lock(m_syncMutex);
m_syncReady = true;
m_syncCV.notify_all();
});
CHECK(nativeToJsBridge_);
}
上线的代码中。催化器对象在启动的流程中的主要作用就完成了。主要就是将催化器初始化的一些Java、Native、JS层的一些通信对象准备好。
我们在回过头去，看catalystInstance.runJSBundle()方法的调用。
@Override
public void runJSBundle() {
Log.d(ReactConstants.TAG, "CatalystInstanceImpl.runJSBundle()");
Log.d(TAG, "FMsg:第九步：runJSBundle() called");
Assertions.assertCondition(!mJSBundleHasLoaded, "JS bundle was already loaded!");
// incrementPendingJSCalls();
mJSBundleLoader.loadScript(CatalystInstanceImpl.this);
synchronized (mJSCallsPendingInitLock) {
// Loading the bundle is queued on the JS thread, but may not have
// run yet. It's safe to set this here, though, since any work it
// gates will be queued on the JS thread behind the load.
mAcceptCalls = true;
for (PendingJSCall function : mJSCallsPendingInit) {
function.call(this);
}
mJSCallsPendingInit.clear();
mJSBundleHasLoaded = true;
}
// This is registered after JS starts since it makes a JS call
Systrace.registerListener(mTraceListener);
}
public static JSBundleLoader createFileLoader(
final String fileName, final String assetUrl, final boolean loadSynchronously) {
Log.d(TAG, "FMsg:第九步：createFileLoader() called with: fileName = [" + fileName + "], assetUrl = [" + assetUrl + "], loadSynchronously = [" + loadSynchronously + "]");
return new JSBundleLoader() {
@Override
public String loadScript(JSBundleLoaderDelegate delegate) {
delegate.loadScriptFromFile(fileName, assetUrl, loadSynchronously);
return fileName;
}
};
}
@Override
public void loadScriptFromFile(String fileName, String sourceURL, boolean loadSynchronously) {
Log.d(TAG, "FMsg:第九步：loadScriptFromFile() called with: fileName = [" + fileName + "], sourceURL = [" + sourceURL + "], loadSynchronously = [" + loadSynchronously + "]");
mSourceURL = sourceURL;
jniLoadScriptFromFile(fileName, sourceURL, loadSynchronously);
}
这个jniLoadScriptFromFile也是一个Native的方法，我们可以看到他会调用到CatalystInstanceImpl.cpp的
void CatalystInstanceImpl::jniLoadScriptFromFile(const std::string& fileName,
const std::string& sourceURL,
bool loadSynchronously) {
LOG(INFO) <<"===========FMsg:CatalystInstanceImpl jniLoadScriptFromFile==============="<<endl;
if (Instance::isIndexedRAMBundle(fileName.c_str())) {
instance_->loadRAMBundleFromFile(fileName, sourceURL, loadSynchronously);
} else {
std::unique_ptr<const JSBigFileString> script;
RecoverableError::runRethrowingAsRecoverable<std::system_error>(
[&fileName, &script]() {
script = JSBigFileString::fromPath(fileName);
});
instance_->loadScriptFromString(std::move(script), sourceURL, loadSynchronously);
}
}
调用到Instancee.cpp的
void Instance::loadScriptFromString(std::unique_ptr<const JSBigString> string,
std::string sourceURL,
bool loadSynchronously) {
LOG(INFO) <<"===========FMsg:Instance loadScriptFromString==============="<<endl;
SystraceSection s("Instance::loadScriptFromString", "sourceURL",
sourceURL);
if (loadSynchronously) {
loadApplicationSync(nullptr, std::move(string), std::move(sourceURL));
} else {
loadApplication(nullptr, std::move(string), std::move(sourceURL));
}
}
void Instance::loadApplication(std::unique_ptr<RAMBundleRegistry> bundleRegistry,
std::unique_ptr<const JSBigString> string,
std::string sourceURL) {
LOG(INFO) <<"===========FMsg:Instance loadApplication=========string======"<<endl;
callback_->incrementPendingJSCalls();
SystraceSection s("Instance::loadApplication", "sourceURL",
sourceURL);
nativeToJsBridge_->loadApplication(std::move(bundleRegistry), std::move(string),
std::move(sourceURL));
}
下面有调用到了
void NativeToJsBridge::loadApplication(
std::unique_ptr<RAMBundleRegistry> bundleRegistry,
std::unique_ptr<const JSBigString> startupScript,
std::string startupScriptSourceURL) {
LOG(INFO) <<"===========FMsg:NativeToJsBridge loadApplication==============="<<endl;
runOnExecutorQueue(
[this,
bundleRegistryWrap=folly::makeMoveWrapper(std::move(bundleRegistry)),
startupScript=folly::makeMoveWrapper(std::move(startupScript)),
startupScriptSourceURL=std::move(startupScriptSourceURL)]
(JSExecutor* executor) mutable {
auto bundleRegistry = bundleRegistryWrap.move();
if (bundleRegistry) {
executor->setBundleRegistry(std::move(bundleRegistry));
}
//executor从runOnExecutorQueue()返回的map中取得，与OnLoad中的JSCJavaScriptExecutorHolder对应，也与
//Java中的JSCJavaScriptExecutor对应。它的实例在JSExecutor.cpp中实现。
try {
LOG(INFO) <<"===========FMsg:NativeToJsBridge executor loadApplicationScript======" << startupScriptSourceURL << "。"<<endl;
executor->loadApplicationScript(std::move(*startupScript),
std::move(startupScriptSourceURL));
} catch (...) {
m_applicationScriptHasFailure = true;
throw;
}
});
}
void NativeToJsBridge::runOnExecutorQueue(std::function<void(JSExecutor*)> task) {
if (*m_destroyed) {
return;
}
std::shared_ptr<bool> isDestroyed = m_destroyed;
m_executorMessageQueueThread->runOnQueue([this, isDestroyed, task=std::move(task)] {
if (*isDestroyed) {
return;
}
// The executor is guaranteed to be valid for the duration of the task because:
// 1. the executor is only destroyed after it is unregistered
// 2. the executor is unregistered on this queue
// 3. we just confirmed that the executor hasn't been unregistered above
task(m_executor.get());
});
}
下面，我们看到他调用了JSIExecutor的loadApplicationScript。下面我们来看一下这个方法的实现。
void JSIExecutor::loadApplicationScript(
std::unique_ptr<const JSBigString> script,
std::string sourceURL) {
SystraceSection s("JSIExecutor::loadApplicationScript");
LOG(INFO) <<"===========FMsg:JSIExecutor loadApplicationScript===============sourceURL = " << sourceURL << "。" <<endl;
// TODO: check for and use precompiled HBC
runtime_->global().setProperty(
*runtime_,
"nativeModuleProxy",
Object::createFromHostObject(
*runtime_, std::make_shared<NativeModuleProxy>(*this)));
runtime_->global().setProperty(
*runtime_,
"nativeFlushQueueImmediate",
Function::createFromHostFunction(
*runtime_,
PropNameID::forAscii(*runtime_, "nativeFlushQueueImmediate"),
1,
[this](
jsi::Runtime &,
const jsi::Value &,
const jsi::Value *args,
size_t count) {
if (count != 1) {
throw std::invalid_argument(
"nativeFlushQueueImmediate arg count must be 1");
}
// 应该是JSIExecutor⾥里里⾯面callNativeModules中的delegate_->callNativeModules
LOG(INFO) <<"===========FMsg:JSIExecutor loadApplicationScript======callNativeModules======="<<endl;
callNativeModules(args[0], false);
return Value::undefined();
}));
runtime_->global().setProperty(
*runtime_,
"nativeCallSyncHook",
Function::createFromHostFunction(
*runtime_,
PropNameID::forAscii(*runtime_, "nativeCallSyncHook"),
1,
[this](
jsi::Runtime &,
const jsi::Value &,
const jsi::Value *args,
size_t count) { return nativeCallSyncHook(args, count); }));
#if DEBUG
runtime_->global().setProperty(
*runtime_,
"globalEvalWithSourceUrl",
Function::createFromHostFunction(
*runtime_,
PropNameID::forAscii(*runtime_, "globalEvalWithSourceUrl"),
1,
[this](
jsi::Runtime &,
const jsi::Value &,
const jsi::Value *args,
size_t count) { return globalEvalWithSourceUrl(args, count); }));
#endif
if (runtimeInstaller_) {
runtimeInstaller_(*runtime_);
}
bool hasLogger(ReactMarker::logTaggedMarker);
std::string scriptName = simpleBasename(sourceURL);
if (hasLogger) {
ReactMarker::logTaggedMarker(
ReactMarker::RUN_JS_BUNDLE_START, scriptName.c_str());
}
//使用Webkit JSC去解释执行JS
runtime_->evaluateJavaScript(
std::make_unique<BigStringBuffer>(std::move(script)), sourceURL);
flush();
if (hasLogger) {
ReactMarker::logMarker(ReactMarker::CREATE_REACT_CONTEXT_STOP);
ReactMarker::logTaggedMarker(
ReactMarker::RUN_JS_BUNDLE_STOP, scriptName.c_str());
}
}
最后代码调用到evaluateJavaScript方法中。这个方法的实现JSCRuntime.cpp中。我们简简单看一下：
jsi::Value JSCRuntime::evaluateJavaScript(
const std::shared_ptr<const jsi::Buffer> &buffer,
const std::string& sourceURL) {
// LOG(INFO) <<"===========FMsg:JSCRuntime evaluateJavaScript===============sourceURL = " << sourceURL << "。" <<endl;
std::string tmp(
reinterpret_cast<const char*>(buffer->data()), buffer->size());
JSStringRef sourceRef = JSStringCreateWithUTF8CString(tmp.c_str());
JSStringRef sourceURLRef = nullptr;
if (!sourceURL.empty()) {
sourceURLRef = JSStringCreateWithUTF8CString(sourceURL.c_str());
}
JSValueRef exc = nullptr;
JSValueRef res =
JSEvaluateScript(ctx_, sourceRef, nullptr, sourceURLRef, 0, &exc);
JSStringRelease(sourceRef);
if (sourceURLRef) {
JSStringRelease(sourceURLRef);
}
checkException(res, exc);
return createValue(res);
}
从上面的代码中，我们我们开始加载JSBundle的逻辑已经执行完毕。但是这个时候其实ReactNative并没有启动起来。
我们下面来看一下启动流程的最后一步：
我们来回到ReactRootView的startReactApplication这个方法中的最后一步：
private void attachToReactInstanceManager() {
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "attachToReactInstanceManager");
Log.d(TAG, "FMsg:attachToReactInstanceManager() called");
try {
if (mIsAttachedToInstance) {
return;
}
mIsAttachedToInstance = true;
// ReactInstanceManager绑定到当前的RootView
Assertions.assertNotNull(mReactInstanceManager).attachRootView(this);
getViewTreeObserver().addOnGlobalLayoutListener(getCustomGlobalLayoutListener());
} finally {
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
}
}
方法很简单，我们来看attachRootView的实现
public void attachRootView(ReactRoot reactRoot) {
Log.d(TAG, "FMsg:attachRootView() called with: reactRoot = [" + reactRoot + "]");
UiThreadUtil.assertOnUiThread();
// ReactInstanceManager 是支持多 RootView 的.其实这个地方大家可以猜想，其实我们的ReactNative的页面，可以作为一个小的页面View
// 附着到宿主Activity上。
mAttachedReactRoots.add(reactRoot);
// Reset reactRoot content as it's going to be populated by the application content from JS.
clearReactRoot(reactRoot);
// If react context is being created in the background, JS application will be started
// automatically when creation completes, as reactRoot reactRoot is part of the attached
// reactRoot reactRoot list.
ReactContext currentContext = getCurrentReactContext();
if (mCreateReactContextThread == null && currentContext != null) {
// 最后，取出 ReactContext，让 ReactRootView 与 CatalystInstance 相关联：
attachRootViewToInstance(reactRoot);
}
}
private void attachRootViewToInstance(final ReactRoot reactRoot) {
Log.d(ReactConstants.TAG, "ReactInstanceManager.attachRootViewToInstance()");
Log.d(TAG, "FMsg:第十步：attachRootViewToInstance() called with: reactRoot = [" + reactRoot + "]");
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "attachRootViewToInstance");
// 首先通过 UIManagerHelper 拿到 UIManager：
// UIManager 是什么呢？它有两个实现类：FabricUIManager、UIManagerModule
// 我们来看后者，它的注释中说：这是一个原生模块，允许JS创建和更新原生视图。其实这个就是我们后来看RN的渲染流程中非常重要的类
UIManager uiManager =
UIManagerHelper.getUIManager(mCurrentReactContext, reactRoot.getUIManagerType());
@Nullable Bundle initialProperties = reactRoot.getAppProperties();
final int rootTag =
uiManager.addRootView(
reactRoot.getRootViewGroup(),
initialProperties == null
? new WritableNativeMap()
: Arguments.fromBundle(initialProperties),
reactRoot.getInitialUITemplate());
reactRoot.setRootViewTag(rootTag);
if (reactRoot.getUIManagerType() == FABRIC) {
// Fabric requires to call updateRootLayoutSpecs before starting JS Application,
// this ensures the root will hace the correct pointScaleFactor.
uiManager.updateRootLayoutSpecs(
rootTag, reactRoot.getWidthMeasureSpec(), reactRoot.getHeightMeasureSpec());
reactRoot.setShouldLogContentAppeared(true);
} else {
Log.d(TAG, "FMsg:第十步：attachRootViewToInstance() called with: reactRoot = [" + reactRoot + "]");
// 这个方法就是我们真的去调用JS的相关代码，我们可以看看这个代码
reactRoot.runApplication();
}
Systrace.beginAsyncSection(
TRACE_TAG_REACT_JAVA_BRIDGE, "pre_rootView.onAttachedToReactInstance", rootTag);
// 这个地方其实，我们有疑问：
// 为什么使用UiThreadUtil.runOnUiThread。而不是
// mCurrentReactContext.runOnUiQueueThread();???
UiThreadUtil.runOnUiThread(
new Runnable() {
@Override
public void run() {
Systrace.endAsyncSection(
TRACE_TAG_REACT_JAVA_BRIDGE, "pre_rootView.onAttachedToReactInstance", rootTag);
reactRoot.onStage(ReactStage.ON_ATTACH_TO_INSTANCE);
}
});
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
}
这个方法的最后一步，我们就可以看到reactRoot.runApplication() 这个方法很明显，就是运行起来JS的相关代码逻辑。
@Override
public void runApplication() {
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "ReactRootView.runApplication");
Log.d(TAG, "FMsg:第十一步：ReactRootView runApplication() called");
try {
if (mReactInstanceManager == null || !mIsAttachedToInstance) {
return;
}
ReactContext reactContext = mReactInstanceManager.getCurrentReactContext();
if (reactContext == null) {
return;
}
CatalystInstance catalystInstance = reactContext.getCatalystInstance();
String jsAppModuleName = getJSModuleName();
if (mUseSurface) {
// TODO call surface's runApplication
} else {
if (mWasMeasured) {
updateRootLayoutSpecs(mWidthMeasureSpec, mHeightMeasureSpec);
}
WritableNativeMap appParams = new WritableNativeMap();
appParams.putDouble("rootTag", getRootViewTag());
@Nullable Bundle appProperties = getAppProperties();
if (appProperties != null) {
appParams.putMap("initialProps", Arguments.fromBundle(appProperties));
}
mShouldLogContentAppeared = true;
Log.i(TAG, "FMsg: 第十步：==============runApplication: ==========================" + jsAppModuleName);
Log.i(TAG, "FMsg: 第十步：==============runApplication: ==========================" + appParams);
catalystInstance.getJSModule(AppRegistry.class).runApplication(jsAppModuleName, appParams);
}
} finally {
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
}
}
这个方法也是比较简单的。通过ReactContext的实例，拿到催化器实例。然后通过催化器实例获取JSModule的runApplication
@Override
public <T extends JavaScriptModule> T getJSModule(Class<T> jsInterface) {
// Log.d(TAG, "FMsg:getJSModule() called with: jsInterface = [" + jsInterface + "]");
// mJSModuleRegistry注入器获取当前的注入器。至于怎么去获取的。我们可以再分析
return mJSModuleRegistry.getJavaScriptModule(this, jsInterface);
}
可以看到，最终调用的是 catalystInstance.getJSModule(AppRegistry.class).runApplication(jsAppModuleName, appParams) ， AppRegistry.class 是JS层暴露给Java层的接口方法。它的真正实现在 AppRegistry.js 里， AppRegistry.js 是运行所有 RN 应用的 JS 层入口，我们来看看它的实现：在 Libraries/ReactNative 中的 AppRegistry.js
/**
* Loads the JavaScript bundle and runs the app.
*
* See http://facebook.github.io/react-native/docs/appregistry.html#runapplication
*/
runApplication(appKey: string, appParameters: any): void {
const msg =
'Running "' + appKey + '" with ' + JSON.stringify(appParameters);
infoLog(msg);
BugReporting.addSource(
'AppRegistry.runApplication' + runCount++,
() => msg,
);
invariant(
runnables[appKey] && runnables[appKey].run,
`"${appKey}" has not been registered. This can happen if:\n` +
'* Metro (the local dev server) is run from the wrong folder. ' +
'Check if Metro is running, stop it and restart it in the current project.\n' +
"* A module failed to load due to an error and `AppRegistry.registerComponent` wasn't called.",
);
SceneTracker.setActiveScene({name: appKey});
runnables[appKey].run(appParameters);
},
到这里就会去调用JS进行渲染，在通过 UIManagerModule 将JS组件转换成Android组件，最终显示在 ReactRootView 上。
最后总结一下，就是先在应用终端启动并创建上下文对象，启动 JS Runtime ，进行布局，将JS端的代码通过C++层， UIManagerMoodule 转化成 Android 组件，再进行渲染，最后将渲染的View添加到 ReactRootView 上，最终呈现在用户面前。
