public void onCreate(Bundle savedInstanceState) {
        ...
        this.flutterView = this.viewFactory.createFlutterView(this.activity);
        if (this.flutterView == null) {
            FlutterNativeView nativeView = this.viewFactory.createFlutterNativeView();
            this.flutterView = new FlutterView(this.activity, (AttributeSet)null, nativeView);
            this.flutterView.setLayoutParams(matchParent);
            this.activity.setContentView(this.flutterView);
            this.launchView = this.createLaunchView();
            if (this.launchView != null) {
                this.addLaunchView();
            }
        }
        ...
    }

public FlutterView(Context context, AttributeSet attrs, FlutterNativeView nativeView) {
            super(context, attrs);
            ...
            //創建在native層的處理對象，相關繪制邏輯其實都是在native層處理的，Java層只負責傳入
            this.mNativeView = new FlutterNativeView(activity.getApplicationContext());
            //創建dart的解釋器
            this.dartExecutor = this.mNativeView.getDartExecutor();
            //創建渲染對象
            this.flutterRenderer = new FlutterRenderer(this.mNativeView.getFlutterJNI());
            //native層的view對象進行綁定   
            this.mNativeView.attachViewAndActivity(this, activity);
            //由于是surfaceView，所以在surface創建好之后傳入naitve
            this.mSurfaceCallback = new Callback() {
                public void surfaceCreated(SurfaceHolder holder) {
                    FlutterView.this.assertAttached();
                    FlutterView.this.mNativeView.getFlutterJNI().onSurfaceCreated(holder.getSurface());
                }
                public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
                    FlutterView.this.assertAttached();
                    FlutterView.this.mNativeView.getFlutterJNI().onSurfaceChanged(width, height);
                }
                public void surfaceDestroyed(SurfaceHolder holder) {
                    FlutterView.this.assertAttached();
                    FlutterView.this.mNativeView.getFlutterJNI().onSurfaceDestroyed();
                }
            };
            this.getHolder().addCallback(this.mSurfaceCallback);
            //
            this.mActivityLifecycleListeners = new ArrayList();
            this.mFirstFrameListeners = new ArrayList();
            this.navigationChannel = new NavigationChannel(this.dartExecutor);
            this.keyEventChannel = new KeyEventChannel(this.dartExecutor);
            this.lifecycleChannel = new LifecycleChannel(this.dartExecutor);
            this.localizationChannel = new LocalizationChannel(this.dartExecutor);
            this.platformChannel = new PlatformChannel(this.dartExecutor);
            this.systemChannel = new SystemChannel(this.dartExecutor);
            this.settingsChannel = new SettingsChannel(this.dartExecutor);
            final PlatformPlugin platformPlugin = new PlatformPlugin(activity, this.platformChannel);
            this.addActivityLifecycleListener(new ActivityLifecycleListener() {
                public void onPostResume() {
                    platformPlugin.updateSystemUiOverlays();
                }
            });
            this.mImm = (InputMethodManager)this.getContext().getSystemService("input_method");
            PlatformViewsController platformViewsController = this.mNativeView.getPluginRegistry().getPlatformViewsController();
            this.mTextInputPlugin = new TextInputPlugin(this, this.dartExecutor, platformViewsController);
            this.androidKeyProcessor = new AndroidKeyProcessor(this.keyEventChannel, this.mTextInputPlugin);
            this.androidTouchProcessor = new AndroidTouchProcessor(this.flutterRenderer);
            this.mNativeView.getPluginRegistry().getPlatformViewsController().attachTextInputPlugin(this.mTextInputPlugin);
            this.sendLocalesToDart(this.getResources().getConfiguration());
            this.sendUserPlatformSettingsToDart();

FlutterView.this.mNativeView.getFlutterJNI().onSurfaceCreated(holder.getSurface());

static void SurfaceCreated(JNIEnv* env,
                           jobject jcaller,
                           jlong shell_holder,
                           jobject jsurface) {
  // Note: This frame ensures that any local references used by
  // ANativeWindow_fromSurface are released immediately. This is needed as a
  // workaround for https://code.google.com/p/android/issues/detail?id=68174
  fml::jni::ScopedJavaLocalFrame scoped_local_reference_frame(env);
  auto window = fml::MakeRefCounted<AndroidNativeWindow>(
      ANativeWindow_fromSurface(env, jsurface));
  ANDROID_SHELL_HOLDER->GetPlatformView()->NotifyCreated(std::move(window));
}

void PlatformViewAndroid::NotifyCreated(
    fml::RefPtr<AndroidNativeWindow> native_window) {
  if (android_surface_) {
    //1
    InstallFirstFrameCallback();
    ...
  }
  //2
  PlatformView::NotifyCreated();
}

void PlatformView::NotifyCreated() {
  std::unique_ptr<Surface> surface;
  ...
  delegate_.OnPlatformViewCreated(std::move(surface));
}

// |PlatformView::Delegate|
void Shell::OnPlatformViewCreated(std::unique_ptr<Surface> surface) {
  TRACE_EVENT0("flutter", "Shell::OnPlatformViewCreated");
  FML_DCHECK(is_setup_);
  FML_DCHECK(task_runners_.GetPlatformTaskRunner()->RunsTasksOnCurrentThread());
 
  ...
  //這里主要是一系列的判斷，避免死鎖
  const bool should_post_raster_task =
      !task_runners_.GetRasterTaskRunner()->RunsTasksOnCurrentThread();
 
  fml::AutoResetWaitableEvent latch;
  //UI線程執行，渲染的流程
  auto raster_task =
      fml::MakeCopyable([&waiting_for_first_frame = waiting_for_first_frame_,
                         rasterizer = rasterizer_->GetWeakPtr(),  //
                         surface = std::move(surface)]() mutable {
        if (rasterizer) {
          // Enables the thread merger which may be used by the external view
          // embedder.
          rasterizer->EnableThreadMergerIfNeeded();
          rasterizer->Setup(std::move(surface));
        }
 
        waiting_for_first_frame.store(true);
      });
  ...
    auto ui_task = [engine = engine_->GetWeakPtr()] {
    if (engine) {
      engine->OnOutputSurfaceCreated();
    }
  };
  ...
    //啟動各種渲染的流程
    fml::TaskRunner::RunNowOrPostTask(task_runners_.GetIOTaskRunner(), io_task);
    latch.Wait();
  if (!should_post_raster_task) {
    // See comment on should_post_raster_task, in this case the raster_task
    // wasn't executed, and we just run it here as the platform thread
    // is the raster thread.
    raster_task();
  }
}