flutter和android原生通信的理解(1)
flutter和android原生通信的理解(2)

android原生的 flutter api

FlutterActivity

 public class FlutterActivity extends Activity {
//...
protected FlutterActivityAndFragmentDelegate delegate;
 @Override
  protected void onCreate(@Nullable Bundle savedInstanceState) {
   //...
    delegate = new FlutterActivityAndFragmentDelegate(this);
    delegate.onAttach(this);
    delegate.onActivityCreated(savedInstanceState);
 //...
  }

  @Override
  protected void onStart() {
    super.onStart();
    lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_START);
    delegate.onStart();
  }

  @Override
  protected void onResume() {
    super.onResume();
   //...
    delegate.onResume();
  }

FlutterFragment

public class FlutterFragment extends Fragment {
 //...
 FlutterActivityAndFragmentDelegate delegate;
 
//...
 @Override
  public void onAttach(@NonNull Context context) {
    super.onAttach(context);
    delegate = new FlutterActivityAndFragmentDelegate(this);
    delegate.onAttach(context);
  }

  @Nullable
  @Override
  public View onCreateView(
      LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    return delegate.onCreateView(inflater, container, savedInstanceState);
  }

 @Override
  public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    delegate.onActivityCreated(savedInstanceState);
  }

  @Override
  public void onStart() {
    super.onStart();
    delegate.onStart();
  }
//...

FlutterActivity 和 FlutterFragment 类都有一个FlutterActivityAndFragmentDelegate delegate 对象；

final class FlutterActivityAndFragmentDelegate {
   private FlutterEngine flutterEngine;
   private FlutterView flutterView;

  void onAttach(@NonNull Context context) {
    //..
    if (flutterEngine == null) {
      setupFlutterEngine();
     }
  }
  void setupFlutterEngine() {
   //...
    flutterEngine =new FlutterEngine(
            host.getContext(),
            host.getFlutterShellArgs().toArray(),
            /*automaticallyRegisterPlugins=*/ false);
   //...
  }

  View onCreateView(
      LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
  

    if (host.getRenderMode() == RenderMode.surface) {
      FlutterSurfaceView flutterSurfaceView =
          new FlutterSurfaceView(
              host.getActivity(), host.getTransparencyMode() == TransparencyMode.transparent);

      //..

      // Create the FlutterView that owns the FlutterSurfaceView.
      flutterView = new FlutterView(host.getActivity(), flutterSurfaceView);
    } else {
      FlutterTextureView flutterTextureView = new FlutterTextureView(host.getActivity());
 //..
      // Create the FlutterView that owns the FlutterTextureView.
      flutterView = new FlutterView(host.getActivity(), flutterTextureView);
    }

    // Add listener to be notified when Flutter renders its first frame.
    flutterView.addOnFirstFrameRenderedListener(flutterUiDisplayListener);

    flutterSplashView = new FlutterSplashView(host.getContext());
    //..
    flutterSplashView.displayFlutterViewWithSplash(flutterView, host.provideSplashScreen());

    Log.v(TAG, "Attaching FlutterEngine to FlutterView.");
    flutterView.attachToFlutterEngine(flutterEngine);

    return flutterSplashView;
  }

• FlutterView 是android原生view的封装；
  持有flutterSurfaceView对象，flutterTextureView对象；

Paints a Flutter UI on a {@link android.view.Surface}.

用来绘制Flutter UI，当然绘制需要借助flutterEngine

• FlutterEngine flutterEngine 是 安卓原生平台 封装的接口
  为了调用Flutter层Engine；

FlutterEngine

public class FlutterEngine {
//都在FlutterEngine 中创建
  @NonNull private final FlutterJNI flutterJNI;
  @NonNull private final FlutterRenderer renderer;
  @NonNull private final DartExecutor dartExecutor;

//..

public FlutterEngine(
      @NonNull Context context,
      @NonNull FlutterLoader flutterLoader,
      @NonNull FlutterJNI flutterJNI,
      @NonNull PlatformViewsController platformViewsController,
      @Nullable String[] dartVmArgs,
      boolean automaticallyRegisterPlugins) {
    this.flutterJNI = flutterJNI;
    //..
    attachToJni();

    this.dartExecutor = new DartExecutor(flutterJNI, context.getAssets());
    this.dartExecutor.onAttachedToJNI();

    // TODO(mattcarroll): FlutterRenderer is temporally coupled to attach(). Remove that coupling if
    // possible.
    this.renderer = new FlutterRenderer(flutterJNI);
  //..
  }

• FlutterJNI flutterJNI;是android原生 调用底层c++的 native接口
• DartExecutor dartExecutor;
  是android原生 调用 Fluter层dart代码的 接口，具体实现肯定离不开FlutterJNI;

DartExecutor

public class DartExecutor {
  //..
  @NonNull private final FlutterJNI flutterJNI;
  @NonNull private final DartMessenger dartMessenger;
  @NonNull private final BinaryMessenger binaryMessenger;//发送消息
  @Nullable private IsolateServiceIdListener isolateServiceIdListener;//接收消息

  private final BinaryMessenger.BinaryMessageHandler isolateChannelMessageHandler =
      new BinaryMessenger.BinaryMessageHandler() {
        @Override
        public void onMessage(ByteBuffer message, final BinaryReply callback) {
          isolateServiceId = StringCodec.INSTANCE.decodeMessage(message);
          if (isolateServiceIdListener != null) {
            isolateServiceIdListener.onIsolateServiceIdAvailable(isolateServiceId);
          }
        }
      };


 public DartExecutor(@NonNull FlutterJNI flutterJNI, @NonNull AssetManager assetManager) {
    this.flutterJNI = flutterJNI;
    //..
    this.dartMessenger = new DartMessenger(flutterJNI);
    dartMessenger.setMessageHandler("flutter/isolate", isolateChannelMessageHandler);
    this.binaryMessenger = new DefaultBinaryMessenger(dartMessenger);
  }
//...

 /** @deprecated Use {@link #getBinaryMessenger()} instead. */
  @Deprecated
  @Override
  @UiThread
  public void send(@NonNull String channel, @Nullable ByteBuffer message) {
    binaryMessenger.send(channel, message);
  }
 
 /**
   * Returns a {@link BinaryMessenger} that can be used to send messages to, and receive messages
   * from, Dart code that this {@code DartExecutor} is executing.
   */
  @NonNull
  public BinaryMessenger getBinaryMessenger() {
    return binaryMessenger;
  }

}

• DartMessenger dartMessenger；信使，用来跟 Flutter层 通信
• BinaryMessenger binaryMessenger; 通过信使 对Flutter层 发送消息
• IsolateServiceIdListener isolateServiceIdListener; 通过信使 接收 来自Flutter层 的消息

Flutter plugin 在android原生的注册

关键是注册MethodChannel 通过FluuterJNI 到底层c++;

 @Override
public void onAttachedToEngine(FlutterPluginBinding flutterPluginBinding) {
        channel = new MethodChannel(flutterPluginBinding.getFlutterEngine().getDartExecutor(), "flutter_datafinder");
        channel.setMethodCallHandler(this);
       //..
    }

//或者,差异在于Flutter 版本1.12前后  注册插件的方法不同；
 public static void registerWith(Registrar registrar) {
        final MethodChannel channel = new MethodChannel(registrar.messenger(), "flutter_datafinder");
        channel.setMethodCallHandler(new FlutterDataFinderPlugin());
        //
        application = (Application) registrar.context().getApplicationContext();
    }

为 MethodChannel 传入 信使的发送对象 BinaryMessenger messenger;
channel.setMethodCallHandler() 为channel设置MethodCallHandler对象；然后MethodCallHandler 包装成为 信使的接收对象，来接收来自Flutter层的消息;

补充