一、初始化流程
在开始分析启动流程之前，我们先从混合开发流程入手，大致分两步。
1.继承ReactActivity，并完成相关初始化工作。
public class MyReactActivity extends Activity implements DefaultHardwareBackBtnHandler {
private ReactRootView mReactRootView;
private ReactInstanceManager mReactInstanceManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mReactRootView = new ReactRootView(this);
mReactInstanceManager = ReactInstanceManager.builder()
.setApplication(getApplication())
.setCurrentActivity(this)
.setBundleAssetName("index.android.bundle")
.setJSMainModulePath("index")
.addPackage(new MainReactPackage())
.setUseDeveloperSupport(BuildConfig.DEBUG)
.setInitialLifecycleState(LifecycleState.RESUMED)
.build();
// The string here (e.g. "MyReactNativeApp") has to match
// the string in AppRegistry.registerComponent() in index.js
mReactRootView.startReactApplication(mReactInstanceManager, "MyReactNativeApp", null);
setContentView(mReactRootView);
}
@Override
public void invokeDefaultOnBackPressed() {
super.onBackPressed();
}
@Override
protected void onPause() {
super.onPause();
if (mReactInstanceManager != null) {
mReactInstanceManager.onHostPause(this);
}
}
@Override
protected void onResume() {
super.onResume();
if (mReactInstanceManager != null) {
mReactInstanceManager.onHostResume(this, this);
}
}
@Override
protected void onDestroy() {
super.onDestroy();
if (mReactInstanceManager != null) {
mReactInstanceManager.onHostDestroy(this);
}
if (mReactRootView != null) {
mReactRootView.unmountReactApplication();
}
}
@Override
public void onBackPressed() {
if (mReactInstanceManager != null) {
mReactInstanceManager.onBackPressed();
} else {
super.onBackPressed();
}
}
}
复制代码注意：
a.实际开发中，一般会写一个单例来获取mReactInstanceManager对象，多个ReactFragment or ReactActivity可以共享同一个mReactInstanceManager对象。
b.mReactRootView作为ReactActivity的根布局，是一个容器View，我们编写的react代码，最终就是被attach到这里的。
2.编写React代码
import React from 'react';
import {AppRegistry, StyleSheet, Text, View} from 'react-native';
class HelloWorld extends React.Component {
render() {
return (
<View style={styles.container}>
<Text style={styles.hello}>Hello, World</Text>
</View>
);
}
}
var styles = StyleSheet.create({
container: {
flex: 1,
justifyContent: 'center',
},
hello: {
fontSize: 20,
textAlign: 'center',
margin: 10,
},
});
AppRegistry.registerComponent('MyReactNativeApp', () => HelloWorld);
复制代码完成以上2步，在增加一些配置操作，相信你应该能把一个demo run起来了。
二、启动流程
启动流程分以下几步：
1 在程序启动的时候，也就是ReactActivity的onCreate()函数中，我们会去创建一个ReactInstanceManager对象，ReactInstanceManager用于管理生命周期，管理ReactRootView，以及一些配置等。
2 ReactRootView作为应用的根视图，通过调用ReactRootView.startReactApplication()方法启动应用。
3 RN应用页面渲染前，需要先创建ReactContext的创建流程在，异步任务ReactContextInitAsyncTask负责来完成这个任务。
4 ReactContextInitAsyncTask在后台ReactContextInitAsyncTask.doInBackground()执行ReactContext的创建，创建ReactContext的过程中，会依据ReactPackage创建JavaScriptModuleRegistry与
NativeModuleRegistry注册表以及它们的管理类CatalystInstanceImpl，同时创建JS、Native与UI线程队列，并最终调用CatalystInstanceImpl.runJSBundle()去异步
加载JS Bundle文件。
5 后台任务执行完成后，在ReactContextInitAsyncTask.onPostExecute()会调用ReactInstanceManager.setupReactContext()设置创建好的ReactContext，并将
ReactRootView加载进来，并调用RN应用的JS入口APPRegistry来启动应用。
6 JS层找到已经注册的对应的启动组件，执行renderApplication()来渲染整个应用。
复制代码按照初始化流程，我们从ReactActivity入手。通过查看源码我们发现，ReactActivity并没有做太多事情，大部分事情的交给了代理类ReactActivityDelegate来实现，那我们一起看看ReactActivityDelegate都干了什么。
public class ReactActivityDelegate {
private final @Nullable Activity mActivity;
private final @Nullable String mMainComponentName;
private @Nullable ReactRootView mReactRootView;
private @Nullable DoubleTapReloadRecognizer mDoubleTapReloadRecognizer;
private @Nullable PermissionListener mPermissionListener;
private @Nullable Callback mPermissionsCallback;
protected ReactRootView createRootView() {
return new ReactRootView(getContext());
}
protected ReactNativeHost getReactNativeHost() {
return ((ReactApplication) getPlainActivity().getApplication()).getReactNativeHost();
}
public ReactInstanceManager getReactInstanceManager() {
return getReactNativeHost().getReactInstanceManager();
}
protected void onCreate(Bundle savedInstanceState) {
String mainComponentName = getMainComponentName();
if (mainComponentName != null) {
loadApp(mainComponentName);
}
mDoubleTapReloadRecognizer = new DoubleTapReloadRecognizer();
}
protected void loadApp(String appKey) {
if (mReactRootView != null) {
throw new IllegalStateException("Cannot loadApp while app is already running.");
}
mReactRootView = createRootView();
mReactRootView.startReactApplication(
getReactNativeHost().getReactInstanceManager(),
appKey,
getLaunchOptions());
getPlainActivity().setContentView(mReactRootView);
}
}
复制代码可以发现，ReactActivityDelegate在创建时主要做了3件事：
1.创建ReactRootView
2.调用mReactRootView的startReactApplication方法，继续执行应用启动流程
3.调用setContentView方法，将mReactRootView作为ReactActivity的content view
复制代码从中不难发现，ReactNative真正的核心就在ReactRootView，，ReactRootView本质上是一个FrameLayout，并没有什么神奇的魔法，好，接下来让我们看看跳进ReactRootView继续我们的启动流程分析。
public void startReactApplication(
ReactInstanceManager reactInstanceManager,
String moduleName,
@Nullable Bundle initialProperties,
@Nullable String initialUITemplate) {
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "startReactApplication");
try {
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
}
if (!mReactInstanceManager.hasStartedCreatingInitialContext()) {
mReactInstanceManager.createReactContextInBackground();
}
attachToReactInstanceManager();
} finally {
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
}
}
复制代码在这个方法中，主要创建了应用的上下文-ReactContext，同时把传入的参数赋给了成员变量。
我们来看看这4个参数：
ReactInstanceManager reactInstanceManager ：管理React实例。
String moduleName：模块的名字，对应ReactActivity.getMainComponentName()与AppRegistry.registerComponent()。
Bundle initialProperties：Bundle类型的数据，可以通过这个参数在startActivity()时传递参数到JS层。
String initialUITemplate：0.59版本并没有用到，可能是代码还没写完吧，尴尬。
复制代码继续我们的启动流程，ReactInstanceManager.createReactContextInBackground()。看名字好像是在后台线程创建上下文，我们跳进去看看。
@ThreadSafe
public class ReactInstanceManager {
@ThreadConfined(UI)
public void createReactContextInBackground() {
Log.d(ReactConstants.TAG, "ReactInstanceManager.createReactContextInBackground()");
Assertions.assertCondition(
!mHasStartedCreatingInitialContext,
"createReactContextInBackground should only be called when creating the react " +
"application for the first time. When reloading JS, e.g. from a new file, explicitly" +
"use recreateReactContextInBackground");
mHasStartedCreatingInitialContext = true;
recreateReactContextInBackgroundInner();
}
@ThreadConfined(UI)
public void recreateReactContextInBackground() {
Assertions.assertCondition(
mHasStartedCreatingInitialContext,
"recreateReactContextInBackground should only be called after the initial " +
"createReactContextInBackground call.");
recreateReactContextInBackgroundInner();
}
@ThreadConfined(UI)
private void recreateReactContextInBackgroundInner() {
Log.d(ReactConstants.TAG, "ReactInstanceManager.recreateReactContextInBackgroundInner()");
PrinterHolder.getPrinter()
.logMessage(ReactDebugOverlayTags.RN_CORE, "RNCore: recreateReactContextInBackground");
UiThreadUtil.assertOnUiThread();
if (mUseDeveloperSupport && mJSMainModulePath != null) {
final DeveloperSettings devSettings = mDevSupportManager.getDevSettings();
// If remote JS debugging is enabled, load from dev server.
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);
return;
}
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 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()");
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()");
UiThreadUtil.assertOnUiThread();
synchronized (mAttachedReactRoots) {
synchronized (mReactContextLock) {
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);
final ReactApplicationContext reactApplicationContext =
createReactContext(
initParams.getJsExecutorFactory().create(),
initParams.getJsBundleLoader());
mCreateReactContextThread = null;
ReactMarker.logMarker(PRE_SETUP_REACT_CONTEXT_START);
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();
}
private ReactApplicationContext createReactContext(
JavaScriptExecutor jsExecutor,
JSBundleLoader jsBundleLoader) {
Log.d(ReactConstants.TAG, "ReactInstanceManager.createReactContext()");
ReactMarker.logMarker(CREATE_REACT_CONTEXT_START, jsExecutor.getName());
//在这里创建ReactContext，ReactApplicationContext继承自ReactContext
final ReactApplicationContext reactContext = new ReactApplicationContext(mApplicationContext);
//查看外部是否设置NativeModuleCallExceptionHandler，它是在ReactInstanceManagerBuilder构建ReactInstanceManager是传递进来的
//如果设置了则使用外部NativeModuleCallExceptionHandler，如果没有设置则使用DevSupportManager。
NativeModuleCallExceptionHandler exceptionHandler = mNativeModuleCallExceptionHandler != null
? mNativeModuleCallExceptionHandler
: mDevSupportManager;
reactContext.setNativeModuleCallExceptionHandler(exceptionHandler);
NativeModuleRegistry nativeModuleRegistry = processPackages(reactContext, mPackages, false);
//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()
.setReactQueueConfigurationSpec(ReactQueueConfigurationSpec.createDefault())
.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 {
catalystInstance = catalystInstanceBuilder.build();
} finally {
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
ReactMarker.logMarker(CREATE_CATALYST_INSTANCE_END);
}
if (mJSIModulePackage != null) {
catalystInstance.addJSIModules(mJSIModulePackage
.getJSIModules(reactContext, catalystInstance.getJavaScriptContextHolder()));
}
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JS Bundle
catalystInstance.runJSBundle();
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
//关联ReacContext与CatalystInstance
reactContext.initializeWithInstance(catalystInstance);
return reactContext;
}
private NativeModuleRegistry processPackages(
ReactApplicationContext reactContext,
List<ReactPackage> packages,
boolean checkAndUpdatePackageMembership) {
//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。
NativeModuleRegistryBuilder nativeModuleRegistryBuilder = new NativeModuleRegistryBuilder(
reactContext,
this);
ReactMarker.logMarker(PROCESS_PACKAGES_START);
// TODO(6818138): Solve use-case of native modules overriding
synchronized (mPackages) {
for (ReactPackage reactPackage : packages) {
if (checkAndUpdatePackageMembership && mPackages.contains(reactPackage)) {
continue;
}
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "createAndProcessCustomReactPackage");
try {
if (checkAndUpdatePackageMembership) {
mPackages.add(reactPackage);
}
// 递归处理我们在Application里注入的ReactPackage，处理的过程就是把各自的Module添加到对应的注册表中。
processPackage(reactPackage, nativeModuleRegistryBuilder);
} finally {
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
}
}
}
ReactMarker.logMarker(PROCESS_PACKAGES_END);
ReactMarker.logMarker(BUILD_NATIVE_MODULE_REGISTRY_START);
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "buildNativeModuleRegistry");
NativeModuleRegistry nativeModuleRegistry;
try {
//生成Java Module注册表
nativeModuleRegistry = nativeModuleRegistryBuilder.build();
} finally {
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
ReactMarker.logMarker(BUILD_NATIVE_MODULE_REGISTRY_END);
}
return nativeModuleRegistry;
}
}
复制代码辗转反侧，最终通过runCreateReactContextOnNewThread开启了一个线程，然后调用createReactContext(JavaScriptExecutor jsExecutor,JSBundleLoader jsBundleLoader)创建了ReactContext。我们重点来看看传入的2给参数：
JavaScriptExecutor jsExecutor：当该类被加载时，它会自动去加载"reactnativejnifb.so"库，并会调用Native方
法initHybrid()初始化C++层RN与JSC通信的框架。
JSBundleLoader jsBundleLoader：缓存了JSBundle的信息，封装了上层加载JSBundle的相关接口，CatalystInstance通过其简介调用ReactBridge去加载JS文件，不同的场景会创建
不同的加载器，具体可以查看类JSBundleLoader。
复制代码createReactContext->processPackages主要做了以下几件事：
1 创建JavaModule注册表并交由CatalystInstance管理。
3 处理ReactPackage，将JavaModule放进对应的注册表里。
3 创建CatalystInstance实例。
4 关联ReactContext与CatalystInstance，并加载JS Bundle。
复制代码接着看catalystInstance.runJSBundle()，该方法的调用栈如下：
CatalystInstanceImpl.runJSBundle() -> JSBundleLoader.loadScript() ->CatalystInstanceImpl.loadScriptFromAssets()/loadScriptFromFile() -> CatalystInstanceImpl.jniLoadScriptFromAssets()/jniLoadScriptFromFile()
-> CatalystInstanceImpl::jniLoadScriptFromAssets()/jniLoadScriptFromFile() -> Instance::loadScriptFromString()/loadScriptFromFile()
-> NativeToJsBridge::loadApplication() -> JSCExecutor::loadApplicationScript()
复制代码最终由C++中的JSCExecutor.cpp完成了JS Bundle的加载，核心逻辑都在JSCExecutor.cpp中，这一块的内容我们后续的文章在详细分析，我们先来看看CatalystInstanceImpl的创建流程。
public class CatalystInstanceImpl implements CatalystInstance {
private CatalystInstanceImpl(
final ReactQueueConfigurationSpec reactQueueConfigurationSpec,
final JavaScriptExecutor jsExecutor,
final NativeModuleRegistry nativeModuleRegistry,
final JSBundleLoader jsBundleLoader,
NativeModuleCallExceptionHandler nativeModuleCallExceptionHandler) {
Log.d(ReactConstants.TAG, "Initializing React Xplat Bridge.");
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "createCatalystInstanceImpl");
// Native方法，用来创建JNI相关状态，并返回mHybridData
mHybridData = initHybrid();
//创建三个核心线程：Native Modules Thread、JS Thread、UI Thread，都是通过Handler来管理的。
mReactQueueConfiguration = ReactQueueConfigurationImpl.create(
reactQueueConfigurationSpec,
new NativeExceptionHandler());
mBridgeIdleListeners = new CopyOnWriteArrayList<>();
mNativeModuleRegistry = nativeModuleRegistry;
// 创建JavaScriptModule注册表
mJSModuleRegistry = new JavaScriptModuleRegistry();
mJSBundleLoader = jsBundleLoader;
mNativeModuleCallExceptionHandler = nativeModuleCallExceptionHandler;
mNativeModulesQueueThread = mReactQueueConfiguration.getNativeModulesQueueThread();
mTraceListener = new JSProfilerTraceListener(this);
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
Log.d(ReactConstants.TAG, "Initializing React Xplat Bridge before initializeBridge");
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "initializeCxxBridge");
//Native方法，创建BridgeCallback实例，初始化Bridge。
initializeBridge(
new BridgeCallback(this),
jsExecutor,
mReactQueueConfiguration.getJSQueueThread(),
mNativeModulesQueueThread,
mNativeModuleRegistry.getJavaModules(this),
mNativeModuleRegistry.getCxxModules());
Log.d(ReactConstants.TAG, "Initializing React Xplat Bridge after initializeBridge");
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
mJavaScriptContextHolder = new JavaScriptContextHolder(getJavaScriptContext());
}
private native void initializeBridge(
ReactCallback callback,
JavaScriptExecutor jsExecutor,
MessageQueueThread jsQueue,
MessageQueueThread moduleQueue,
Collection<JavaModuleWrapper> javaModules,
Collection<ModuleHolder> cxxModules);
}
复制代码从CatalystInstanceImpl的构建过程可以看出，CatalystInstanceImpl是个封装管理类，封装了各种注册表，以及初始化JNI，我们来看看最后初始化Bridge传入的6个参数：
ReactCallback callback：CatalystInstanceImpl的静态内部类ReactCallback，负责接口回调。
JavaScriptExecutor jsExecutor：JS执行器，将JS的调用传递给C++层。
MessageQueueThread jsQueue.getJSQueueThread()：JS线程，通过mReactQueueConfiguration.getJSQueueThread()获得，mReactQueueConfiguration通过ReactQueueConfigurationSpec.createDefault()创建。
MessageQueueThread moduleQueue：Native线程，通过mReactQueueConfiguration.getNativeModulesQueueThread()获得，mReactQueueConfiguration通过ReactQueueConfigurationSpec.createDefault()创建。
Collection<JavaModuleWrapper> javaModules：java modules，来源于mJavaRegistry.getJavaModules(this)。
Collection<ModuleHolder> cxxModules)：c++ modules，来源于mJavaRegistry.getCxxModules()。
复制代码我们接着看，CatalystInstanceImpl.runJSBundle()
@Override
public void runJSBundle() {
Log.d(ReactConstants.TAG, "CatalystInstanceImpl.runJSBundle()");
Assertions.assertCondition(!mJSBundleHasLoaded, "JS bundle was already loaded!");
// incrementPendingJSCalls();
//调用加载器加载JS Bundle，不同情况下加载器不同。
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);
}
复制代码接着调用JSBundleLoader.loadScript
public abstract class JSBundleLoader {
/**
* This loader is recommended one for release version of your app. In that case local JS executor
* should be used. JS bundle will be read from assets in native code to save on passing large
* strings from java to native memory.
*/
// 从assets文件加载
public static JSBundleLoader createAssetLoader(
final Context context,
final String assetUrl,
final boolean loadSynchronously) {
return new JSBundleLoader() {
@Override
public String loadScript(JSBundleLoaderDelegate delegate) {
delegate.loadScriptFromAssets(context.getAssets(), assetUrl, loadSynchronously);
return assetUrl;
}
};
}
/**
* This loader loads bundle from file system. The bundle will be read in native code to save on
* passing large strings from java to native memory.
*/
public static JSBundleLoader createFileLoader(final String fileName) {
return createFileLoader(fileName, fileName, false);
}
// 从文件加载
public static JSBundleLoader createFileLoader(
final String fileName,
final String assetUrl,
final boolean loadSynchronously) {
return new JSBundleLoader() {
@Override
public String loadScript(JSBundleLoaderDelegate delegate) {
delegate.loadScriptFromFile(fileName, assetUrl, loadSynchronously);
return fileName;
}
};
}
/**
* This loader is used when bundle gets reloaded from dev server. In that case loader expect JS
* bundle to be prefetched and stored in local file. We do that to avoid passing large strings
* between java and native code and avoid allocating memory in java to fit whole JS bundle in it.
* Providing correct {@param sourceURL} of downloaded bundle is required for JS stacktraces to
* work correctly and allows for source maps to correctly symbolize those.
*/
//从缓存加载
public static JSBundleLoader createCachedBundleFromNetworkLoader(
final String sourceURL,
final String cachedFileLocation) {
return new JSBundleLoader() {
@Override
public String loadScript(JSBundleLoaderDelegate delegate) {
try {
delegate.loadScriptFromFile(cachedFileLocation, sourceURL, false);
return sourceURL;
} catch (Exception e) {
throw DebugServerException.makeGeneric(e.getMessage(), e);
}
}
};
}
/**
* This loader is used to load delta bundles from the dev server. We pass each delta message to
* the loader and process it in C++. Passing it as a string leads to inefficiencies due to memory
* copies, which will have to be addressed in a follow-up.
* @param nativeDeltaClient
*/
// 从dev server加载
public static JSBundleLoader createDeltaFromNetworkLoader(
final String sourceURL,
final NativeDeltaClient nativeDeltaClient) {
return new JSBundleLoader() {
@Override
public String loadScript(JSBundleLoaderDelegate delegate) {
try {
delegate.loadScriptFromDeltaBundle(sourceURL, nativeDeltaClient, false);
return sourceURL;
} catch (Exception e) {
throw DebugServerException.makeGeneric(e.getMessage(), e);
}
}
};
}
/**
* This loader is used when proxy debugging is enabled. In that case there is no point in fetching
* the bundle from device as remote executor will have to do it anyway.
*/
// debug时加载
public static JSBundleLoader createRemoteDebuggerBundleLoader(
final String proxySourceURL,
final String realSourceURL) {
return new JSBundleLoader() {
@Override
public String loadScript(JSBundleLoaderDelegate delegate) {
delegate.setSourceURLs(realSourceURL, proxySourceURL);
return realSourceURL;
}
};
}
/** Loads the script, returning the URL of the source it loaded. */
public abstract String loadScript(JSBundleLoaderDelegate delegate);
}
复制代码接下来我们以CatalystInstanceImpl.loadScriptFromAssets()举例。
@Override
public void loadScriptFromAssets(AssetManager assetManager, String assetURL, boolean loadSynchronously) {
mSourceURL = assetURL;
jniLoadScriptFromAssets(assetManager, assetURL, loadSynchronously);
}
复制代码可以看出该方法最终调用Native方法jniLoadScriptFromAssets去加载JS Bundle，来到CatalystInstanceImpl.cpp。
void CatalystInstanceImpl::jniLoadScriptFromAssets(
jni::alias_ref<JAssetManager::javaobject> assetManager,
const std::string& assetURL,
bool loadSynchronously) {
const int kAssetsLength = 9; // strlen("assets://");
// 获取source js Bundle的路径名
auto sourceURL = assetURL.substr(kAssetsLength);
//获取AssetManager对象。
auto manager = extractAssetManager(assetManager);
//读取JS Bundle里的内容。
auto script = loadScriptFromAssets(manager, sourceURL);
// 判断是不是unbundle命令打包，build.gradle默认里是bundle打包方式。
if (JniJSModulesUnbundle::isUnbundle(manager, sourceURL)) {
auto bundle = JniJSModulesUnbundle::fromEntryFile(manager, sourceURL);
auto registry = RAMBundleRegistry::singleBundleRegistry(std::move(bundle));
instance_->loadRAMBundle(
std::move(registry),
std::move(script),
sourceURL,
loadSynchronously);
return;
} else {
//bundle命令打包走此流程
instance_->loadScriptFromString(std::move(script), sourceURL, loadSynchronously);
}
}
关于unbundle命令
<unbundle命令，使用方式和bundle命令完全相同。unbundle命令是在bundle命令的基础上增加了一项功能，除了生成整合JS文件index.android.bundle外，还会
生成各个单独的未整合JS文件（但会被优化），全部放在js-modules目录下，同时会生成一个名为UNBUNDLE的标识文件，一并放在其中。UNBUNDLE标识文件的前4个字节
固定为0xFB0BD1E5，用于加载前的校验。
复制代码接着会调用Instance.cpp的loadScriptFromString()方法去解析JS Bundle里的内容。
void Instance::loadScriptFromString(std::unique_ptr<const JSBigString> string,
std::string sourceURL,
bool loadSynchronously) {
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));
}
}
复制代码进一步调用NativeToJsBridge.cpp的loadApplication()方法，它的实现如下所示：
void NativeToJsBridge::loadApplication(
std::unique_ptr<RAMBundleRegistry> bundleRegistry,
std::unique_ptr<const JSBigString> startupScript,
std::string startupScriptSourceURL) {
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));
}
try {
//Java中的JSCJavaScriptExecutor对应。它的实例在JSIExecutor.cpp中实现。
executor->loadApplicationScript(std::move(*startupScript),
std::move(startupScriptSourceURL));
} catch (...) {
m_applicationScriptHasFailure = true;
throw;
}
});
}
复制代码进一步调用JSIExecutor.cpp的loadApplicationScript()方法。
void JSIExecutor::loadApplicationScript(
std::unique_ptr<const JSBigString> script,
std::string sourceURL) {
SystraceSection s("JSIExecutor::loadApplicationScript");
// 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");
}
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 (runtimeInstaller_) {
runtimeInstaller_(*runtime_);
}
bool hasLogger(ReactMarker::logTaggedMarker);
std::string scriptName = simpleBasename(sourceURL);
if (hasLogger) {
ReactMarker::logTaggedMarker(
ReactMarker::RUN_JS_BUNDLE_START, scriptName.c_str());
}
// //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());
}
}
void JSIExecutor::flush() {
SystraceSection s("JSIExecutor::flush");
if (flushedQueue_) {
callNativeModules(flushedQueue_->call(*runtime_), true);
return;
}
// When a native module is called from JS, BatchedBridge.enqueueNativeCall()
// is invoked. For that to work, require('BatchedBridge') has to be called,
// and when that happens, __fbBatchedBridge is set as a side effect.
Value batchedBridge =
runtime_->global().getProperty(*runtime_, "__fbBatchedBridge");
// So here, if __fbBatchedBridge doesn't exist, then we know no native calls
// have happened, and we were able to determine this without forcing
// BatchedBridge to be loaded as a side effect.
if (!batchedBridge.isUndefined()) {
// If calls were made, we bind to the JS bridge methods, and use them to
// get the pending queue of native calls.
//绑定bridge
bindBridge();
//把JS层相关通信数据通过flushedQUeue()
//返回给callNativeModules
callNativeModules(flushedQueue_->call(*runtime_), true);
} else if (delegate_) {
// If we have a delegate, we need to call it; we pass a null list to
// callNativeModules, since we know there are no native calls, without
// calling into JS again. If no calls were made and there's no delegate,
// nothing happens, which is correct.
callNativeModules(nullptr, true);
}
void JSIExecutor::bindBridge() {
std::call_once(bindFlag_, [this] {
SystraceSection s("JSIExecutor::bindBridge (once)");
Value batchedBridgeValue =
runtime_->global().getProperty(*runtime_, "__fbBatchedBridge");
if (batchedBridgeValue.isUndefined()) {
throw JSINativeException(
"Could not get BatchedBridge, make sure your bundle is packaged correctly");
}
Object batchedBridge = batchedBridgeValue.asObject(*runtime_);
callFunctionReturnFlushedQueue_ = batchedBridge.getPropertyAsFunction(
*runtime_, "callFunctionReturnFlushedQueue");
invokeCallbackAndReturnFlushedQueue_ = batchedBridge.getPropertyAsFunction(
*runtime_, "invokeCallbackAndReturnFlushedQueue");
flushedQueue_ =
batchedBridge.getPropertyAsFunction(*runtime_, "flushedQueue");
callFunctionReturnResultAndFlushedQueue_ =
batchedBridge.getPropertyAsFunction(
*runtime_, "callFunctionReturnResultAndFlushedQueue");
});
}
void JSIExecutor::callNativeModules(const Value &queue, bool isEndOfBatch) {
SystraceSection s("JSIExecutor::callNativeModules");
// If this fails, you need to pass a fully functional delegate with a
// module registry to the factory/ctor.
CHECK(delegate_) << "Attempting to use native modules without a delegate";
#if 0 // maybe useful for debugging
std::string json = runtime_->global().getPropertyAsObject(*runtime_, "JSON")
.getPropertyAsFunction(*runtime_, "stringify").call(*runtime_, queue)
.getString(*runtime_).utf8(*runtime_);
#endif
//m_delegate为JsToNativeBridge对象。
delegate_->callNativeModules(
*this, dynamicFromValue(*runtime_, queue), isEndOfBatch);
}
}
复制代码m_flushedQueueJS支线的是MessageQueue.js的flushedQueue()方法，此时JS已经被加载到队列中，等待Java层来驱动它。加载完JS后，返回reactApplicationContext，我们继续跟进它的实现。
@ThreadConfined(UI)
private void runCreateReactContextOnNewThread(final ReactContextInitParams initParams) {
Log.d(ReactConstants.TAG, "ReactInstanceManager.runCreateReactContextOnNewThread()");
UiThreadUtil.assertOnUiThread();
synchronized (mAttachedReactRoots) {
synchronized (mReactContextLock) {
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);
final ReactApplicationContext reactApplicationContext =
createReactContext(
initParams.getJsExecutorFactory().create(),
initParams.getJsBundleLoader());
mCreateReactContextThread = null;
ReactMarker.logMarker(PRE_SETUP_REACT_CONTEXT_START);
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();
}
复制代码接着调用 setupReactContext(reactApplicationContext);
private void setupReactContext(final ReactApplicationContext reactContext) {
Log.d(ReactConstants.TAG, "ReactInstanceManager.setupReactContext()");
ReactMarker.logMarker(PRE_SETUP_REACT_CONTEXT_END);
ReactMarker.logMarker(SETUP_REACT_CONTEXT_START);
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "setupReactContext");
synchronized (mAttachedReactRoots) {
synchronized (mReactContextLock) {
mCurrentReactContext = Assertions.assertNotNull(reactContext);
}
CatalystInstance catalystInstance =
Assertions.assertNotNull(reactContext.getCatalystInstance());
// Native Java module的初始化
catalystInstance.initialize();
mDevSupportManager.onNewReactContextCreated(reactContext);
mMemoryPressureRouter.addMemoryPressureListener(catalystInstance);
//复位生命周期
moveReactContextToCurrentLifecycleState();
ReactMarker.logMarker(ATTACH_MEASURED_ROOT_VIEWS_START);
//遍历ReactRootView
for (ReactRoot reactRoot : mAttachedReactRoots) {
//遍历ReactRootView
attachRootViewToInstance(reactRoot);
}
ReactMarker.logMarker(ATTACH_MEASURED_ROOT_VIEWS_END);
}
ReactInstanceEventListener[] listeners =
new ReactInstanceEventListener[mReactInstanceEventListeners.size()];
final ReactInstanceEventListener[] finalListeners =
mReactInstanceEventListeners.toArray(listeners);
UiThreadUtil.runOnUiThread(
new Runnable() {
@Override
public void run() {
for (ReactInstanceEventListener listener : finalListeners) {
listener.onReactContextInitialized(reactContext);
}
}
});
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
ReactMarker.logMarker(SETUP_REACT_CONTEXT_END);
reactContext.runOnJSQueueThread(
new Runnable() {
@Override
public void run() {
Process.setThreadPriority(Process.THREAD_PRIORITY_DEFAULT);
ReactMarker.logMarker(CHANGE_THREAD_PRIORITY, "js_default");
}
});
reactContext.runOnNativeModulesQueueThread(
new Runnable() {
@Override
public void run() {
Process.setThreadPriority(Process.THREAD_PRIORITY_DEFAULT);
}
});
}
复制代码reactRootView的attach操作。
private void attachRootViewToInstance(final ReactRoot reactRoot) {
Log.d(ReactConstants.TAG, "ReactInstanceManager.attachRootViewToInstance()");
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "attachRootViewToInstance");
UIManager uiManagerModule = UIManagerHelper.getUIManager(mCurrentReactContext, reactRoot.getUIManagerType());
@Nullable Bundle initialProperties = reactRoot.getAppProperties();
// 将ReactRootView作为根布局
final int rootTag = uiManagerModule.addRootView(
reactRoot.getRootViewGroup(),
initialProperties == null ?
new WritableNativeMap() : Arguments.fromBundle(initialProperties),
reactRoot.getInitialUITemplate());
reactRoot.setRootViewTag(rootTag);
//启动流程入口
reactRoot.runApplication();
Systrace.beginAsyncSection(
TRACE_TAG_REACT_JAVA_BRIDGE,
"pre_rootView.onAttachedToReactInstance",
rootTag);
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);
}
复制代码reactRoot.runApplication(),我们跟进去看一下。
@Override
public void runApplication() {
Systrace.beginSection(TRACE_TAG_REACT_JAVA_BRIDGE, "ReactRootView.runApplication");
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));
}
if (getUIManagerType() == FABRIC) {
appParams.putBoolean("fabric", true);
}
mShouldLogContentAppeared = true;
catalystInstance.getJSModule(AppRegistry.class).runApplication(jsAppModuleName, appParams);
}
} finally {
Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
}
}
复制代码ReactInstanceManager.attachMeasuredRootViewToInstance()最终进入了RN应用的启动流程入口，调用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：
//上面代码最终调用的就是这个函数
runApplication(appKey: string, appParameters: any): void {
const msg =
'Running application "' + appKey + '" with appParams: ' +
JSON.stringify(appParameters) + '. ' +
'__DEV__ === ' + String(__DEV__) +
', development-level warning are ' + (__DEV__ ? 'ON' : 'OFF') +
', performance optimizations are ' + (__DEV__ ? 'OFF' : 'ON');
infoLog(msg);
BugReporting.addSource('AppRegistry.runApplication' + runCount++, () => msg);
invariant(
runnables[appKey] && runnables[appKey].run,
'Application ' + appKey + ' has not been registered.\n\n' +
'Hint: This error often happens when you\'re running the packager ' +
'(local dev server) from a wrong folder. For example you have ' +
'multiple apps and the packager is still running for the app you ' +
'were working on before.\nIf this is the case, simply kill the old ' +
'packager instance (e.g. close the packager terminal window) ' +
'and start the packager in the correct app folder (e.g. cd into app ' +
'folder and run \'npm start\').\n\n' +
'This error can also happen due to a require() error during ' +
'initialization or failure to call AppRegistry.registerComponent.\n\n'
);
runnables[appKey].run(appParameters);
},
复制代码到这里就会去调用JS进行组件渲染，再通过Java层的UIManagerModule将JS组件转换为Android组件，最终显示在ReactRootView上，下期我们再见。