整个flutter引擎的相关初始化工作在onCreate方法里开始的:
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
switchLaunchThemeForNormalTheme();
super.onCreate(savedInstanceState);
lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_CREATE);
delegate = new FlutterActivityAndFragmentDelegate(this);
///创建绑定引擎等
delegate.onAttach(this);
///用于插件、框架恢复状态
delegate.onActivityCreated(savedInstanceState);
///设置窗口背景透明，隐藏 status bar
configureWindowForTransparency();
///这里是咱们的入口
setContentView(createFlutterView());
configureStatusBarForFullscreenFlutterExperience();
}
setContentView大家很熟悉，我们直接看createFlutterView（） 这个方法：
@NonNull
private View createFlutterView() {
return delegate.onCreateView(
null /* inflater /, null / container /, null / savedInstanceState */);
}
FlutterActivityAndFragmentDelegate
flutter的初始化、启动等操作都是委托给它的。
我们继续看onCreateView，我将说明以注释的形式写在代码里
@NonNull
View onCreateView(
LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
Log.v(TAG, “Creating FlutterView.”);
ensureAlive();
if (host.getRenderMode() == RenderMode.surface) {
/// flutter 应用在surface上显示，所以会进入到这里
FlutterSurfaceView flutterSurfaceView =
new FlutterSurfaceView(
host.getActivity(), host.getTransparencyMode() == TransparencyMode.transparent);
// Allow our host to customize FlutterSurfaceView, if desired.
host.onFlutterSurfaceViewCreated(flutterSurfaceView);
// Create the FlutterView that owns the FlutterSurfaceView.
///用我们的flutterSurfaceView 初始化了一个 FlutterView
flutterView = new FlutterView(host.getActivity(), flutterSurfaceView);
} else {
FlutterTextureView flutterTextureView = new FlutterTextureView(host.getActivity());
// Allow our host to customize FlutterSurfaceView, if desired.
host.onFlutterTextureViewCreated(flutterTextureView);
// 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);
/// 创建一个闪屏view - FlutterSplashView
flutterSplashView = new FlutterSplashView(host.getContext());
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
flutterSplashView.setId(View.generateViewId());
} else {
// TODO(mattcarroll): Find a better solution to this ID. This is a random, static ID.
// It might conflict with other Views, and it means that only a single FlutterSplashView
// can exist in a View hierarchy at one time.
flutterSplashView.setId(486947586);
}
/// 显示闪屏页
flutterSplashView.displayFlutterViewWithSplash(flutterView, host.provideSplashScreen());
Log.v(TAG, “Attaching FlutterEngine to FlutterView.”);
///所创建surface 绑定到engine上
flutterView.attachToFlutterEngine(flutterEngine);
return flutterSplashView;
}
这里我们可以大致了解到，创建了一个FlutterSurfaceView 它继承自surfaceView(我们的flutter页面也是渲染在这个surface上的)。之后我们用它初始化一个FlutterView，
FlutterView继承自 FrameLayout
随后我们再创建一个FlutterSplashView （继承FrameLayout）并调用displayFlutterViewWithSplash（）方法。
public void displayFlutterViewWithSplash(
@NonNull FlutterView flutterView, @Nullable SplashScreen splashScreen) {
// If we were displaying a previous FlutterView, remove it.
if (this.flutterView != null) {
this.flutterView.removeOnFirstFrameRenderedListener(flutterUiDisplayListener);
removeView(this.flutterView);
}
// If we were displaying a previous splash screen View, remove it.
if (splashScreenView != null) {
removeView(splashScreenView);
}
// Display the new FlutterView.
this.flutterView = flutterView;
///添加flutterView
addView(flutterView);
this.splashScreen = splashScreen;
// Display the new splash screen, if needed.
if (splashScreen != null) {
if (isSplashScreenNeededNow()) {
Log.v(TAG, “Showing splash screen UI.”);
// This is the typical case. A FlutterEngine is attached to the FlutterView and we’re
// waiting for the first frame to render. Show a splash UI until that happens.
splashScreenView = splashScreen.createSplashView(getContext(), splashScreenState);
///添加 splashScreenView
addView(this.splashScreenView);
flutterView.addOnFirstFrameRenderedListener(flutterUiDisplayListener);
} else if (isSplashScreenTransitionNeededNow()) {
Log.v(
TAG,
“Showing an immediate splash transition to Flutter due to previously interrupted transition.”);
splashScreenView = splashScreen.createSplashView(getContext(), splashScreenState);
addView(splashScreenView);
transitionToFlutter();
} else if (!flutterView.isAttachedToFlutterEngine()) {
Log.v(
TAG,
“FlutterView is not yet attached to a FlutterEngine. Showing nothing until a FlutterEngine is attached.”);
flutterView.addFlutterEngineAttachmentListener(flutterEngineAttachmentListener);
}
}
}
这个方法对flutterView进行了保存（不用管这个），随后我们保存了一个 接口的实现类——splashScreen，这个实现类则是由FlutterActivity实现的(MainActivity)来提供的:
///host 是个接口，由FlutterActivity实现
回顾上面：flutterSplashView.displayFlutterViewWithSplash(flutterView, host.provideSplashScreen());
public SplashScreen provideSplashScreen() {
Drawable manifestSplashDrawable = getSplashScreenFromManifest();
if (manifestSplashDrawable != null) {
///DrawableSplashScreen 实现了 splashScreen的接口
return new DrawableSplashScreen(manifestSplashDrawable);
} else {
return null;
}
}
通过getSplashScreenFromManifest 初始化了一个drawable，我们看一下它内部：
@Nullable
@SuppressWarnings(“deprecation”)
private Drawable getSplashScreenFromManifest() {
try {
ActivityInfo activityInfo =
getPackageManager().getActivityInfo(getComponentName(), PackageManager.GET_META_DATA);
Bundle metadata = activityInfo.metaData;
///这里就是我们在 AndroidManifest.xml中设置启动页了
///SPLASH_SCREEN_META_DATA_KEY 的值 见下方
int splashScreenId = metadata != null ? metadata.getInt(SPLASH_SCREEN_META_DATA_KEY) : 0;
return splashScreenId != 0
? Build.VERSION.SDK_INT > Build.VERSION_CODES.LOLLIPOP
-
? getResources().getDrawable(splashScreenId, getTheme())
-
getResources().getDrawable(splashScreenId)
-
null;
} catch (PackageManager.NameNotFoundException e) {
// This is never expected to happen.
return null;
}
}
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