Revert "Prevent long flash when switching to Flutter app. (flutter#47903) (flutter#16527)"

This reverts commit 95f7aa3.

Author: NoamDev

shell/platform/android/io/flutter/embedding/android/FlutterActivityAndFragmentDelegate.java

@@ -12,6 +12,7 @@
 import android.content.Intent;
 import android.os.Build;
 import android.os.Bundle;
+import android.os.Handler;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.annotation.VisibleForTesting;
@@ -237,14 +238,8 @@ void onAttach(@NonNull Context context) {
    *
    * <p>{@code inflater} and {@code container} may be null when invoked from an {@code Activity}.
    *
-   * <p>This method:
-   *
-   * <ol>
-   *   <li>creates a new {@link FlutterView} in a {@code View} hierarchy
-   *   <li>adds a {@link FlutterUiDisplayListener} to it
-   *   <li>attaches a {@link FlutterEngine} to the new {@link FlutterView}
-   *   <li>returns the new {@code View} hierarchy
-   * </ol>
+   * <p>This method creates a new {@link FlutterView}, adds a {@link FlutterUiDisplayListener} to
+   * it, and then returns it.
    */
   @NonNull
   View onCreateView(
@@ -266,9 +261,6 @@ View onCreateView(
     }
     flutterSplashView.displayFlutterViewWithSplash(flutterView, host.provideSplashScreen());
 
-    Log.v(TAG, "Attaching FlutterEngine to FlutterView.");
-    flutterView.attachToFlutterEngine(flutterEngine);
-
     return flutterSplashView;
   }
 
@@ -289,13 +281,31 @@ void onActivityCreated(@Nullable Bundle bundle) {
    * <p>
    *
    * <ol>
+   *   <li>Attaches the {@link FlutterEngine} owned by this delegate to the {@link FlutterView}
+   *       owned by this delegate.
    *   <li>Begins executing Dart code, if it is not already executing.
    * </ol>
    */
   void onStart() {
     Log.v(TAG, "onStart()");
     ensureAlive();
-    doInitialFlutterViewRun();
+
+    // We post() the code that attaches the FlutterEngine to our FlutterView because there is
+    // some kind of blocking logic on the native side when the surface is connected. That lag
+    // causes launching Activitys to wait a second or two before launching. By post()'ing this
+    // behavior we are able to move this blocking logic to after the Activity's launch.
+    // TODO(mattcarroll): figure out how to avoid blocking the MAIN thread when connecting a surface
+    new Handler()
+        .post(
+            new Runnable() {
+              @Override
+              public void run() {
+                Log.v(TAG, "Attaching FlutterEngine to FlutterView.");
+                flutterView.attachToFlutterEngine(flutterEngine);
+
+                doInitialFlutterViewRun();
+              }
+            });
   }
 
   /**
@@ -408,6 +418,7 @@ void onStop() {
     Log.v(TAG, "onStop()");
     ensureAlive();
     flutterEngine.getLifecycleChannel().appIsPaused();
+    flutterView.detachFromFlutterEngine();
   }
 
   /**
@@ -418,8 +429,6 @@ void onStop() {
   void onDestroyView() {
     Log.v(TAG, "onDestroyView()");
     ensureAlive();
-
-    flutterView.detachFromFlutterEngine();
     flutterView.removeOnFirstFrameRenderedListener(flutterUiDisplayListener);
   }