React Native之启动流程

import { AppRegistry } from 'react-native'
 ...省略代码

 AppRegistry.registerComponent('demo', () => Index)

public class MainApplication extends Application implements ReactApplication {
    //ReactNativeHost：持有ReactInstanceManager实例，做一些初始化操作。
  private final ReactNativeHost mReactNativeHost = new ReactNativeHost(this) {
    @Override
    public boolean getUseDeveloperSupport() {
      return BuildConfig.DEBUG;
    }

    @Override
    protected List<ReactPackage> getPackages() {
      return Arrays.<ReactPackage>asList(
          new MainReactPackage()
      );
    }
  };

  @Override
  public ReactNativeHost getReactNativeHost() {
    return mReactNativeHost;
  }

  @Override
  public void onCreate() {
    super.onCreate();
    //SoLoader：加载C++底层库，准备解析JS。
    SoLoader.init(this, /* native exopackage */ false);
  }
}
}

public class MainActivity extends ReactActivity {

    @Override
    protected String getMainComponentName() {
        return "demo";
    }
}

public abstract class ReactActivity extends Activity
    implements DefaultHardwareBackBtnHandler, PermissionAwareActivity {
    private final ReactActivityDelegate mDelegate;

    ...省略代码

     @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    mDelegate.onCreate(savedInstanceState);
  }    
}

public class ReactActivityDelegate {
      protected void onCreate(Bundle savedInstanceState) {
      // 弹框权限判断
    boolean needsOverlayPermission = false;
    if (getReactNativeHost().getUseDeveloperSupport() && Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
      // Get permission to show redbox in dev builds.
      if (!Settings.canDrawOverlays(getContext())) {
        needsOverlayPermission = true;
        Intent serviceIntent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, Uri.parse("package:" + getContext().getPackageName()));
        FLog.w(ReactConstants.TAG, REDBOX_PERMISSION_MESSAGE);
        Toast.makeText(getContext(), REDBOX_PERMISSION_MESSAGE, Toast.LENGTH_LONG).show();
        ((Activity) getContext()).startActivityForResult(serviceIntent, REQUEST_OVERLAY_PERMISSION_CODE);
      }
    }
        // 加载组建逻辑 mMainComponentName为getMainComponentName返回的值
    if (mMainComponentName != null && !needsOverlayPermission) {
      loadApp(mMainComponentName);
    }
    // 双击判断工具类
    mDoubleTapReloadRecognizer = new DoubleTapReloadRecognizer();
  }

  protected void loadApp(String appKey) {
     //空判断
    if (mReactRootView != null) {
      throw new IllegalStateException("Cannot loadApp while app is already running.");
    }
    // 创建 RN容器根视图
    mReactRootView = createRootView();
    mReactRootView.startReactApplication(
      getReactNativeHost().getReactInstanceManager(),
      appKey,
      getLaunchOptions());
      //将rootview添加入activity
    getPlainActivity().setContentView(mReactRootView);
  }
}

public void startReactApplication(
      ReactInstanceManager reactInstanceManager,
      String moduleName,
      @Nullable Bundle initialProperties) {
        ...省略代码
    try {
        //在UI线程中进行
      UiThreadUtil.assertOnUiThread();

      Assertions.assertCondition(
        mReactInstanceManager == null,
        "This root view has already been attached to a catalyst instance manager");
        // 赋值
      mReactInstanceManager = reactInstanceManager;
      mJSModuleName = moduleName;
      mAppProperties = initialProperties;
        // 判断ReactContext是否初始化，没有就异步进行初始化
      if (!mReactInstanceManager.hasStartedCreatingInitialContext()) {
        mReactInstanceManager.createReactContextInBackground();
      }
        //宽高计算完成后添加布局监听
      attachToReactInstanceManager();
    } finally {
      Systrace.endSection(TRACE_TAG_REACT_JAVA_BRIDGE);
    }
  }

public void createReactContextInBackground() {
    //首次执行
     mHasStartedCreatingInitialContext = true;
    recreateReactContextInBackgroundInner();
}