Flutter启动页(闪屏页)的具体实现及原理详析

public class SplashActivity extends FlutterActivity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 GeneratedPluginRegistrant.registerWith(this);
 }
}

 <activity
 android:name=".SplashActivity"
 android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
 android:hardwareAccelerated="true"
 android:launchMode="singleTop"
 android:theme="@style/LaunchTheme"
 android:windowSoftInputMode="adjustResize">
 <meta-data
 android:name="io.flutter.app.android.SplashScreenUntilFirstFrame"
 android:value="true" />
 <intent-filter>
 <action android:name="android.intent.action.MAIN" />
 <category android:name="android.intent.category.LAUNCHER" />
 </intent-filter>
 </activity>

public final class FlutterActivityDelegate
 implements FlutterActivityEvents,
  FlutterView.Provider,
  PluginRegistry {
 private static final String SPLASH_SCREEN_META_DATA_KEY = "io.flutter.app.android.SplashScreenUntilFirstFrame";

 private View launchView;

 @Override
 public void onCreate(Bundle savedInstanceState) {
 String[] args = getArgsFromIntent(activity.getIntent());
 FlutterMain.ensureInitializationComplete(activity.getApplicationContext(), args);
 flutterView = viewFactory.createFlutterView(activity);
 if (flutterView == null) {
 FlutterNativeView nativeView = viewFactory.createFlutterNativeView();
 flutterView = new FlutterView(activity, null, nativeView);
 flutterView.setLayoutParams(matchParent);
 activity.setContentView(flutterView);
 launchView = createLaunchView();//1
 if (launchView != null) {
 addLaunchView();//2
 }
 }
 }

 private View createLaunchView() {
 if (!showSplashScreenUntilFirstFrame()) {//3
 return null;
 }
 final Drawable launchScreenDrawable = getLaunchScreenDrawableFromActivityTheme();
 final View view = new View(activity);
 view.setBackground(launchScreenDrawable);
 return view;
 }

 private Drawable getLaunchScreenDrawableFromActivityTheme() {
 //省略了部分代码
 try {
 return activity.getResources().getDrawable(typedValue.resourceId);
 } catch (NotFoundException e) {
 return null;
 }
 }

 private Boolean showSplashScreenUntilFirstFrame() {
 try {
 ActivityInfo activityInfo = activity.getPackageManager().getActivityInfo(
 activity.getComponentName(),
 PackageManager.GET_META_DATA|PackageManager.GET_ACTIVITIES);
 Bundle metadata = activityInfo.metaData;
 return metadata != null && metadata.getBoolean(SPLASH_SCREEN_META_DATA_KEY);
 } catch (NameNotFoundException e) {
 return false;
 }
 }

 private void addLaunchView() {
 activity.addContentView(launchView, matchParent);//4
 flutterView.addFirstFrameListener(new FlutterView.FirstFrameListener() {//5
 @Override
 public void onFirstFrame() {
 FlutterActivityDelegate.this.launchView.animate()
  .alpha(0f)
  .setListener(new AnimatorListenerAdapter() {
  @Override
  public void onAnimationEnd(Animator animation) {
  ((ViewGroup) FlutterActivityDelegate.this.launchView.getParent())
  .removeView(FlutterActivityDelegate.this.launchView);//5
  }
  });
 }
 });
 activity.setTheme(android.R.style.Theme_Black_NoTitleBar);
 }
}

<resources>
 <style name="LaunchTheme" parent="@android:style/Theme.Black.NoTitleBar">
 <!-- Show a splash screen on the activity. Automatically removed when
 Flutter draws its first frame -->
 <item name="android:windowBackground">@drawable/launch_background</item>
 </style>
</resources>

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android"
 android:opacity="opaque">
 <item>
 <bitmap android:src="@mipmap/ic_launch_bg" />
 </item>
 <item
 android:width="90dp"
 android:height="90dp"
 android:gravity="center">
 <bitmap android:src="@mipmap/ic_launch_logo" />
 </item>
</layer-list>