FlutterView

  • 继承SurfaceView，它的外部有两个线程即主线程和渲染线程，应用渲染线程中向屏幕上绘图能够防止主线程阻塞，从而进步了程序的反应速度。应用了双缓冲机制。
  • 实现BinaryMesaenger接口， 这个接口定义了Android代码和Flutter代码间接通信的形式，此接口还有2个外部接口。 FlutterView实现了这个接口，领有了和flutter通信的的能力
  • 实现TextureRegistry接口，这个接口次要是创立一个SurfaceTexture对象，应用SurfaceTextureEntry包装起来，领有惟一的ID。
  • 实现onAccessibilityChanged接口，次要用来监听系统accessibility 状态变动的。

  • 创立一大堆Channel用于Android和flutter通信

        navigationChannel = new NavigationChannel(dartExecutor);    keyEventChannel = new KeyEventChannel(dartExecutor);    lifecycleChannel = new LifecycleChannel(dartExecutor);    localizationChannel = new LocalizationChannel(dartExecutor);    platformChannel = new PlatformChannel(dartExecutor);    systemChannel = new SystemChannel(dartExecutor);    settingsChannel = new SettingsChannel(dartExecutor);

  • 创立FlutterNativeView

     //初始化 mNativeView = new FlutterNativeView(activity.getApplicationContext()); OnAccessibilityChangeListener AccessibilityStateChangeListener

  • 创立一堆成员变量

    mIsSoftwareRenderingEnabled 硬件加速渲染相干的

    dartExecutor = mNativeView.getDartExecutor();    flutterRenderer = new FlutterRenderer(mNativeView.getFlutterJNI());    mIsSoftwareRenderingEnabled = mNativeView.getFlutterJNI().nativeGetIsSoftwareRenderingEnabled();    mMetrics = new ViewportMetrics();    mMetrics.devicePixelRatio = context.getResources().getDisplayMetrics().density;    setFocusable(true);    setFocusableInTouchMode(true);        //attach到以后Activity    mNativeView.attachViewAndActivity(this, activity);    mSurfaceCallback =        new SurfaceHolder.Callback() {          @Override          public void surfaceCreated(SurfaceHolder holder) {            assertAttached();            mNativeView.getFlutterJNI().onSurfaceCreated(holder.getSurface());          }          @Override          public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {            assertAttached();            mNativeView.getFlutterJNI().onSurfaceChanged(width, height);          }          @Override          public void surfaceDestroyed(SurfaceHolder holder) {            assertAttached();            mNativeView.getFlutterJNI().onSurfaceDestroyed();          }        };

FlutterNativeView

  1. 创立
if (nativeView == null) {      mNativeView = new FlutterNativeView(activity.getApplicationContext());    } else {      mNativeView = nativeView;    }  public FlutterNativeView(@NonNull Context context, boolean isBackgroundView) {    mContext = context;    mPluginRegistry = new FlutterPluginRegistry(this, context);    mFlutterJNI = new FlutterJNI();    mFlutterJNI.addIsDisplayingFlutterUiListener(flutterUiDisplayListener);    this.dartExecutor = new DartExecutor(mFlutterJNI, context.getAssets());    mFlutterJNI.addEngineLifecycleListener(new EngineLifecycleListenerImpl());    attach(this, isBackgroundView);    assertAttached();  }
  • FlutterPluginRegistry是actitiy和flutterView绑定关系操作类，而FlutterJNI创立时，将绑定绘制、跨平台通信、生命周期的监听办法。
  • mFlutterJNI ，Engine层c++办法的一个封装类。所有Flutter JNI的调用都汇合在这个类中。 一个FlutterJNI对象是和一个Platform View相关联，所以蕴含一个nativePlatformViewId来标识
 attach(this, isBackgroundView);  private void attach(FlutterNativeView view, boolean isBackgroundView) {    mFlutterJNI.attachToNative(isBackgroundView);    dartExecutor.onAttachedToJNI();  }  public void attachToNative(boolean isBackgroundView) {    ensureRunningOnMainThread();    ensureNotAttachedToNative();    nativePlatformViewId = nativeAttach(this, isBackgroundView);  }

总结

  1. FlutterView提供了SurfaceView来绘制Flutter的UI
  2. 同时把Android的生命周期、点击事件等信息发送给Flutter。
  3. FlutterView并不负责间接和Flutter Engine通信，具体的通信性能在FlutterNativeView
  4. FlutterNativeView外部有一个FlutterJNI，它负责调用Flutter Engine的C++代码。

java到c++调用

public void attachToNative(boolean isBackgroundView) {    ensureRunningOnMainThread();    ensureNotAttachedToNative();    nativePlatformViewId = nativeAttach(this, isBackgroundView);  }//nativeAttach对应bool RegisterApi(JNIEnv* env) {  static const JNINativeMethod flutter_jni_methods[] = {      // Start of methods from FlutterJNI      {          .name = "nativeAttach",          .signature = "(Lio/flutter/embedding/engine/FlutterJNI;Z)J",          .fnPtr = reinterpret_cast<void*>(&AttachJNI),      },    //对应到AttachJNI    static jlong AttachJNI(JNIEnv* env,                       jclass clazz,                       jobject flutterJNI,                       jboolean is_background_view) {  fml::jni::JavaObjectWeakGlobalRef java_object(env, flutterJNI);  std::shared_ptr<PlatformViewAndroidJNI> jni_facade =      std::make_shared<PlatformViewAndroidJNIImpl>(java_object);  auto shell_holder = std::make_unique<AndroidShellHolder>(      FlutterMain::Get().GetSettings(), jni_facade, is_background_view);  if (shell_holder->IsValid()) {    return reinterpret_cast<jlong>(shell_holder.release());  } else {    return 0;  }}    //创立auto shell_holder = std::make_unique<AndroidShellHolder>//对应flutter/shell/platform/android/android_shell_holder.cc    AndroidShellHolder::AndroidShellHolder创建对象

engine初始化

AndroidShellHolder::AndroidShellHolder(    flutter::Settings settings,    std::shared_ptr<PlatformViewAndroidJNI> jni_facade,    bool is_background_view)    : settings_(std::move(settings)), jni_facade_(jni_facade) {  static size_t shell_count = 1;  auto thread_label = std::to_string(shell_count++);  FML_CHECK(pthread_key_create(&thread_destruct_key_, ThreadDestructCallback) ==            0);  if (is_background_view) {    thread_host_ = {thread_label, ThreadHost::Type::UI};  } else {    thread_host_ = {thread_label, ThreadHost::Type::UI | ThreadHost::Type::GPU |                                      ThreadHost::Type::IO};  }  // Detach from JNI when the UI and raster threads exit.  auto jni_exit_task([key = thread_destruct_key_]() {    FML_CHECK(pthread_setspecific(key, reinterpret_cast<void*>(1)) == 0);  });  thread_host_.ui_thread->GetTaskRunner()->PostTask(jni_exit_task);  if (!is_background_view) {    thread_host_.raster_thread->GetTaskRunner()->PostTask(jni_exit_task);  }  fml::WeakPtr<PlatformViewAndroid> weak_platform_view;  //创立PlatformViewAndroid  //创立on_create_platform_view  Shell::CreateCallback<PlatformView> on_create_platform_view =      [is_background_view, &jni_facade, &weak_platform_view](Shell& shell) {        std::unique_ptr<PlatformViewAndroid> platform_view_android;        if (is_background_view) {          platform_view_android = std::make_unique<PlatformViewAndroid>(              shell,                   // delegate              shell.GetTaskRunners(),  // task runners              jni_facade               // JNI interop          );        } else {          platform_view_android = std::make_unique<PlatformViewAndroid>(              shell,                   // delegate              shell.GetTaskRunners(),  // task runners              jni_facade,              // JNI interop              shell.GetSettings()                  .enable_software_rendering  // use software rendering          );        }        weak_platform_view = platform_view_android->GetWeakPtr();        return platform_view_android;      };  Shell::CreateCallback<Rasterizer> on_create_rasterizer = [](Shell& shell) {    return std::make_unique<Rasterizer>(shell, shell.GetTaskRunners(),                                        shell.GetIsGpuDisabledSyncSwitch());  };  // 创立四个线程 并把以后线程设置platform thread  fml::MessageLoop::EnsureInitializedForCurrentThread();  fml::RefPtr<fml::TaskRunner> gpu_runner;  fml::RefPtr<fml::TaskRunner> ui_runner;  fml::RefPtr<fml::TaskRunner> io_runner;  fml::RefPtr<fml::TaskRunner> platform_runner =      fml::MessageLoop::GetCurrent().GetTaskRunner();  if (is_background_view) {    auto single_task_runner = thread_host_.ui_thread->GetTaskRunner();    gpu_runner = single_task_runner;    ui_runner = single_task_runner;    io_runner = single_task_runner;  } else {    gpu_runner = thread_host_.raster_thread->GetTaskRunner();    ui_runner = thread_host_.ui_thread->GetTaskRunner();    io_runner = thread_host_.io_thread->GetTaskRunner();  }  flutter::TaskRunners task_runners(thread_label,     // label                                    platform_runner,  // platform                                    gpu_runner,       // raster                                    ui_runner,        // ui                                    io_runner         // io  );//shell创立//不论是iOS，Android，linux，嵌入式平台，都有对应的 Shell::Create，差别最大的应该是web端，web端的整体架构形式就齐全不同。//Create的 时候传入platform view create  shell_ =      Shell::Create(task_runners,             // task runners                    GetDefaultWindowData(),   // window data                    settings_,                // settings                    on_create_platform_view,  // platform view create callback                    on_create_rasterizer      // rasterizer create callback      );  platform_view_ = weak_platform_view;  FML_DCHECK(platform_view_);  is_valid_ = shell_ != nullptr;  if (is_valid_) {    task_runners.GetRasterTaskRunner()->PostTask([]() {      // Android describes -8 as "most important display threads, for      // compositing the screen and retrieving input events". Conservatively      // set the raster thread to slightly lower priority than it.      if (::setpriority(PRIO_PROCESS, gettid(), -5) != 0) {        // Defensive fallback. Depending on the OEM, it may not be possible        // to set priority to -5.        if (::setpriority(PRIO_PROCESS, gettid(), -2) != 0) {          FML_LOG(ERROR) << "Failed to set GPU task runner priority";        }      }    });    task_runners.GetUITaskRunner()->PostTask([]() {      if (::setpriority(PRIO_PROCESS, gettid(), -1) != 0) {        FML_LOG(ERROR) << "Failed to set UI task runner priority";      }    });  }}

Shell::Create中调用shell = CreateShellOnPlatformThread，而后回调on_create_platform_view

std::unique_ptr<Shell> Shell::CreateShellOnPlatformThread中过程

  1. 创立shell
  auto shell =      std::unique_ptr<Shell>(new Shell(std::move(vm), task_runners, settings));
  1. 创立platform view
  auto platform_view = on_create_platform_view(*shell.get());  if (!platform_view || !platform_view->GetWeakPtr()) {    return nullptr;
  1. 创立rasterizer
     std::promise<std::unique_ptr<Rasterizer>> rasterizer_promise;     auto rasterizer_future = rasterizer_promise.get_future();     std::promise<fml::WeakPtr<SnapshotDelegate>> snapshot_delegate_promise;     auto snapshot_delegate_future = snapshot_delegate_promise.get_future();     fml::TaskRunner::RunNowOrPostTask(         task_runners.GetRasterTaskRunner(), [&rasterizer_promise,  //                                              &snapshot_delegate_promise,                                              on_create_rasterizer,  //                                              shell = shell.get()    //     ]() {           TRACE_EVENT0("flutter", "ShellSetupGPUSubsystem");           std::unique_ptr<Rasterizer> rasterizer(on_create_rasterizer(*shell));           snapshot_delegate_promise.set_value(rasterizer->GetSnapshotDelegate());           rasterizer_promise.set_value(std::move(rasterizer));         });
  1. 创立 IO manager
    std::promise<std::unique_ptr<ShellIOManager>> io_manager_promise;    auto io_manager_future = io_manager_promise.get_future();    std::promise<fml::WeakPtr<ShellIOManager>> weak_io_manager_promise;    auto weak_io_manager_future = weak_io_manager_promise.get_future();    std::promise<fml::RefPtr<SkiaUnrefQueue>> unref_queue_promise;    auto unref_queue_future = unref_queue_promise.get_future();    auto io_task_runner = shell->GetTaskRunners().GetIOTaskRunner();
  1. 创立 engine
    std::promise<std::unique_ptr<Engine>> engine_promise;    auto engine_future = engine_promise.get_future();    fml::TaskRunner::RunNowOrPostTask(        shell->GetTaskRunners().GetUITaskRunner(),        fml::MakeCopyable([&engine_promise,                                 //                           shell = shell.get(),                             //                           &dispatcher_maker,                               //                           &window_data,                                    //                           isolate_snapshot = std::move(isolate_snapshot),  //                           vsync_waiter = std::move(vsync_waiter),          //                           &weak_io_manager_future,                         //                           &snapshot_delegate_future,                       //                           &unref_queue_future                              //    ]() mutable {          TRACE_EVENT0("flutter", "ShellSetupUISubsystem");          const auto& task_runners = shell->GetTaskRunners();            // The animator is owned by the UI thread but it gets its vsync pulses          // from the platform.          auto animator = std::make_unique<Animator>(*shell, task_runners,                                                     std::move(vsync_waiter));            engine_promise.set_value(std::make_unique<Engine>(              *shell,                         //              dispatcher_maker,               //              *shell->GetDartVM(),            //              std::move(isolate_snapshot),    //              task_runners,                   //              window_data,                    //              shell->GetSettings(),           //              std::move(animator),            //              weak_io_manager_future.get(),   //              unref_queue_future.get(),       //              snapshot_delegate_future.get()  //              ));        }));