FlutterActivityDelegate初始化UI相關的內容

FlutterUI提供了Flutter for Android 的包，FlutterActivity,FlutterFragmentActivity,在平臺側初始化Flutter engine中的信息，上一篇中分析了Dart文件加載Android側的代碼Android加載Dart文件，第二步就是把Flutter相關的代碼繪製出來，經過兩個步驟初始化:platform_view_android_jni.cc這個類做爲Android平臺的UI調用的JNI接口

執行下述的三步操做，可以建立Flutter engine執行環境，傳遞Android端的SurfaceView給到Flutter engine，方便Flutter engine繪製相關的UI界面，執行完成上述步驟，Android側的SurfaceView已經注入到flutter引擎中，後續的文件見控制上面兩個步驟在flutter引擎中是如何工做。

在上一篇文章中調用System.load加載Flutter.so文件到Java性能機中，相關的so邏輯已經初始化文件，接下來須要把相關的Flutter相關的文件路徑傳遞到Flutter.so中進行加載執行

1.調用的nativeAttach:

• io.flutter.embedding.engine.FlutterJNI
• engine/src/flutter/shell/platform/android/platform_view_android_jni.cc,初始化flutter engine 運行環境Platform，GPU，IO,UI,MessageLoop,初始化DartVM，加載第三方庫，skia，ICU等，
• 加載配置//engine/src/flutter/common/settings.cc

2.SurfaceView

• public void surfaceCreated(SurfaceHolder holder) {}
• public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {}
• public void surfaceDestroyed(SurfaceHolder holder) {}

3. nativeDetach

刪除engine/src/flutter/shell/platform/android/android_shell_holder.cc清理運行環境 

FlutterActivityDelegate

使用代理類來處理相關的事件，Flutter是一個UI庫

• 初始化windown窗口
• 獲取Intent參數
• 所有Flutter抽取完成
• 初始化FlutterView,主要管理SurfaceView的初始化，註冊系統事件
• 添加SurfaceView到Activity窗口

public final class FlutterActivityDelegate implements FlutterActivityEvents, Provider, PluginRegistry {

    public void onCreate(Bundle savedInstanceState) {
        <!-- 判斷平臺特性，處理相關window邏輯 -->
        if (VERSION.SDK_INT >= 21) {
            Window window = this.activity.getWindow();
            window.addFlags(-2147483648);
            window.setStatusBarColor(1073741824);
            window.getDecorView().setSystemUiVisibility(1280);
        }
        <!-- 獲取intent參數 -->
        String[] args = getArgsFromIntent(this.activity.getIntent());
        <!-- 所有Flutter相關的文件初始化完成 -->
        FlutterMain.ensureInitializationComplete(this.activity.getApplicationContext(), args);
        this.flutterView = this.viewFactory.createFlutterView(this.activity);
        if (this.flutterView == null) {
        <!-- FlutterNativeView主要用於FlutterView操做JIN的方法邏輯進行封裝 -->
            FlutterNativeView nativeView = this.viewFactory.createFlutterNativeView();
            this.flutterView = new FlutterView(this.activity, (AttributeSet)null, nativeView);
            this.flutterView.setLayoutParams(matchParent);
            <!-- 添加SurfaceView到Activity窗口中 -->
            this.activity.setContentView(this.flutterView);
            <!-- 插件Flutter的啓動界面 -->
            this.launchView = this.createLaunchView();
            if (this.launchView != null) {
                this.addLaunchView();
            }
        }

        if (!this.loadIntent(this.activity.getIntent())) {
            String appBundlePath = FlutterMain.findAppBundlePath(this.activity.getApplicationContext());
            if (appBundlePath != null) {
                this.runBundle(appBundlePath);
            }

        }
    }
複製代碼

FlutterView

1.初始化DartExecutor執行相關的邏輯 2.負責處理FlutterUI相關的內容，建立SurfaceView提供給DartVM渲染FlutterUI代碼 3.註冊常規的Platform事件

public FlutterView(Context context, AttributeSet attrs, FlutterNativeView nativeView) {
    //FlutterNativeView FlutterUI與JNI傳遞信息的類，確保不爲空
    if (nativeView == null) {
        this.mNativeView = new FlutterNativeView(activity.getApplicationContext());
    } else {
        this.mNativeView = nativeView;
    }

    this.dartExecutor = new DartExecutor(this.mNativeView.getFlutterJNI());
    <!-- 判斷是否開啓軟件渲染 engine/src/flutter/common/settings.cc -->
    this.mIsSoftwareRenderingEnabled = FlutterJNI.nativeGetIsSoftwareRenderingEnabled();
    this.mAnimationScaleObserver = new FlutterView.AnimationScaleObserver(new Handler());
    this.mMetrics = new FlutterView.ViewportMetrics();
    <!-- mSurfaceCallback回調方法 -->
    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();
        }
    };
    <!-- 使用平臺通道和Flutter engine進行通訊 -->
    this.navigationChannel = new NavigationChannel(this.dartExecutor);
    this.keyEventChannel = new KeyEventChannel(this.dartExecutor);
    this.lifecycleChannel = new LifecycleChannel(this.dartExecutor);
    this.systemChannel = new SystemChannel(this.dartExecutor);
    this.settingsChannel = new SettingsChannel(this.dartExecutor);
    this.mFlutterLocalizationChannel = new MethodChannel(this, "flutter/localization", JSONMethodCodec.INSTANCE);
    PlatformPlugin platformPlugin = new PlatformPlugin(activity);
    MethodChannel flutterPlatformChannel = new MethodChannel(this, "flutter/platform", JSONMethodCodec.INSTANCE);
    flutterPlatformChannel.setMethodCallHandler(platformPlugin);
    this.addActivityLifecycleListener(platformPlugin);
    this.mImm = (InputMethodManager)this.getContext().getSystemService("input_method");
    this.mTextInputPlugin = new TextInputPlugin(this);
    this.androidKeyProcessor = new AndroidKeyProcessor(this.keyEventChannel);
    this.setLocales(this.getResources().getConfiguration());
    this.sendUserPlatformSettingsToDart();
}
複製代碼

FlutterNativeView

構造函數中調用attach調用FlutterJNI中的nativeAttach調用JNI方法進入platform_view_android_jni.cc初始化AndroidShellHolder，FlutterNativeView主要處理UI和JNI層的邏輯，FlutterJNI,直接與JNI通訊的邏輯，調用Attach對Flutter engine運行環境進行調用，初始化環境

public FlutterNativeView(Context context, boolean isBackgroundView) {
    this.mNextReplyId = 1;
    this.mPendingReplies = new HashMap();
    this.mContext = context;
    this.mPluginRegistry = new FlutterPluginRegistry(this, context);
    this.mFlutterJNI = new FlutterJNI();
    this.mFlutterJNI.setRenderSurface(new FlutterNativeView.RenderSurfaceImpl());
    this.mFlutterJNI.setPlatformMessageHandler(new FlutterNativeView.PlatformMessageHandlerImpl());
    this.mFlutterJNI.addEngineLifecycleListener(new FlutterNativeView.EngineLifecycleListenerImpl());
    <!-- 主要功能是初始化AndroidShellHolder的管理類 -->
    this.attach(this, isBackgroundView);
    this.assertAttached();
    this.mMessageHandlers = new HashMap();
}

複製代碼

AndroidShellHolder

engine/src/flutter/shell/platform/android/platform_view_android_jni.cc,flutterView在初始化時完成android_shell_holder的初始化，方法註冊進入JNI，主要的做用是對AndroidShellHolder進行初始

static jlong AttachJNI(JNIEnv* env, jclass clazz, jobject flutterJNI, jboolean is_background_view) {
  fml::jni::JavaObjectWeakGlobalRef java_object(env, flutterJNI);
  // 初始化shellholder
  auto shell_holder = std::make_unique<AndroidShellHolder>(
      FlutterMain::Get().GetSettings(), java_object, is_background_view);
  if (shell_holder->IsValid()) {
    return reinterpret_cast<jlong>(shell_holder.release());
  } else {
    return 0;
  }
}
複製代碼

!!! WARNING "從這裏開始就是初始化相關的環境，包括MessageLoop,Platform,GPU,UI,IO線程進行建立，加載第三方庫，建立DartVM提供一個能夠運行Dart代碼的環境。後續文件回調Flutter Engine進行初始化進行擴展"

FlutterView

本地SurfaceView初始化完成以後提供給FlutterUI繪製的接口，Flutter使用skia引擎繪製2D圖像，把Platform相關的View注入到Flutter engine中提供能夠繪製的UI給skia進行圖像繪製

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();
  }
};

複製代碼

engine/src/flutter/shell/platform/android/platform_view_android_jni.cc,android本地Surface建立時調用android本地窗口進行繪製ANativeWindow_fromSurface,使用AnativeWindow本地接口提供給本地接口使用

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));
}



static void SurfaceChanged(JNIEnv* env, jobject jcaller, jlong shell_holder, jint width, jint height) {
  ANDROID_SHELL_HOLDER->GetPlatformView()->NotifyChanged(
      SkISize::Make(width, height));
}


static void SurfaceDestroyed(JNIEnv* env, jobject jcaller, jlong shell_holder) {
  ANDROID_SHELL_HOLDER->GetPlatformView()->NotifyDestroyed();
}

複製代碼

至此，Android端的View的初始化就已經完成，等待DartVM執行相關的代碼來完成相關的繪製工做,Android端的 View 的初始化比較簡單，後續再對JNI層的代碼進行分析。