Android Embedding PR25: Prevent black rectangle when launching FlutterActivity (#8460)

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

@@ -9,6 +9,8 @@ import android.content.Intent;
 import android.content.pm.ActivityInfo;
 import android.content.pm.ApplicationInfo;
 import android.content.pm.PackageManager;
+import android.graphics.Color;
+import android.graphics.drawable.Drawable;
 import android.os.Build;
 import android.os.Bundle;
 import android.support.annotation.NonNull;
@@ -16,6 +18,7 @@ import android.support.annotation.Nullable;
 import android.support.v4.app.FragmentActivity;
 import android.support.v4.app.FragmentManager;
 import android.util.Log;
+import android.util.TypedValue;
 import android.view.View;
 import android.view.ViewGroup;
 import android.view.Window;
@@ -24,6 +27,7 @@ import android.widget.FrameLayout;
 
 import io.flutter.embedding.engine.FlutterEngine;
 import io.flutter.embedding.engine.FlutterShellArgs;
+import io.flutter.embedding.engine.renderer.OnFirstFrameRenderedListener;
 import io.flutter.plugin.platform.PlatformPlugin;
 import io.flutter.view.FlutterMain;
 
@@ -61,7 +65,7 @@ import io.flutter.view.FlutterMain;
  * {@code Fragment}.
  */
 // TODO(mattcarroll): explain each call forwarded to Fragment (first requires resolution of PluginRegistry API).
-public class FlutterActivity extends FragmentActivity {
+public class FlutterActivity extends FragmentActivity implements OnFirstFrameRenderedListener {
   private static final String TAG = "FlutterActivity";
 
   // Meta-data arguments, processed from manifest XML.
@@ -82,6 +86,10 @@ public class FlutterActivity extends FragmentActivity {
   private static final int FRAGMENT_CONTAINER_ID = 609893468; // random number
   private FlutterFragment flutterFragment;
 
+  // Used to cover the Activity until the 1st frame is rendered so as to
+  // avoid a brief black flicker from a SurfaceView version of FlutterView.
+  private View coverView;
+
   /**
    * Creates an {@link Intent} that launches a {@code FlutterActivity}, which executes
    * a {@code main()} Dart entrypoint, and displays the "/" route as Flutter's initial route.
@@ -147,10 +155,64 @@ public class FlutterActivity extends FragmentActivity {
     Log.d(TAG, "onCreate()");
     super.onCreate(savedInstanceState);
     setContentView(createFragmentContainer());
+    showCoverView();
     configureStatusBarForFullscreenFlutterExperience();
     ensureFlutterFragmentCreated();
   }
 
+  /**
+   * Cover all visible {@code Activity} area with a {@code View} that paints everything the same
+   * color as the {@code Window}.
+   * <p>
+   * This cover {@code View} should be displayed at the very beginning of the {@code Activity}'s
+   * lifespan and then hidden once Flutter renders its first frame. The purpose of this cover is to
+   * cover {@link FlutterSurfaceView}, which briefly displays a black rectangle before it can make
+   * itself transparent.
+   */
+  private void showCoverView() {
+    // Create the coverView.
+    if (coverView == null) {
+      coverView = new View(this);
+      addContentView(coverView, new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));
+    }
+
+    // Pain the coverView with the Window's background.
+    Drawable background = createCoverViewBackground();
+    if (background != null) {
+      coverView.setBackground(background);
+    } else {
+      // If we can't obtain a window background to replicate then we'd be guessing as to the least
+      // intrusive color. But there is no way to make an accurate guess. In this case we don't
+      // give the coverView any color, which means a brief black rectangle will be visible upon
+      // Activity launch.
+    }
+  }
+
+  @Nullable
+  private Drawable createCoverViewBackground() {
+    TypedValue typedValue = new TypedValue();
+    boolean hasBackgroundColor = getTheme().resolveAttribute(
+        android.R.attr.windowBackground,
+        typedValue,
+        true
+    );
+    if (hasBackgroundColor && typedValue.resourceId != 0) {
+      return getResources().getDrawable(typedValue.resourceId, getTheme());
+    } else {
+      return null;
+    }
+  }
+
+  /**
+   * Hides the cover {@code View}.
+   * <p>
+   * This method should be called when Flutter renders its first frame. See {@link #showCoverView()}
+   * for details.
+   */
+  private void hideCoverView() {
+    coverView.setVisibility(View.GONE);
+  }
+
   private void configureStatusBarForFullscreenFlutterExperience() {
     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
       Window window = getWindow();
@@ -360,4 +422,9 @@ public class FlutterActivity extends FragmentActivity {
   private boolean isDebuggable() {
     return (getApplicationInfo().flags & ApplicationInfo.FLAG_DEBUGGABLE) != 0;
   }
+
+  @Override
+  public void onFirstFrameRendered() {
+    hideCoverView();
+  }
 }

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

@@ -21,6 +21,7 @@ import android.view.ViewGroup;
 import io.flutter.embedding.engine.FlutterEngine;
 import io.flutter.embedding.engine.FlutterShellArgs;
 import io.flutter.embedding.engine.dart.DartExecutor;
+import io.flutter.embedding.engine.renderer.OnFirstFrameRenderedListener;
 import io.flutter.plugin.platform.PlatformPlugin;
 import io.flutter.view.FlutterMain;
 
@@ -214,16 +215,27 @@ public class FlutterFragment extends Fragment {
   @Nullable
   private PlatformPlugin platformPlugin;
 
+  private final OnFirstFrameRenderedListener onFirstFrameRenderedListener = new OnFirstFrameRenderedListener() {
+    @Override
+    public void onFirstFrameRendered() {
+      // Notify our subclasses that the first frame has been rendered.
+      FlutterFragment.this.onFirstFrameRendered();
+
+      // Notify our owning Activity that the first frame has been rendered.
+      FragmentActivity fragmentActivity = getActivity();
+      if (fragmentActivity != null && fragmentActivity instanceof OnFirstFrameRenderedListener) {
+        OnFirstFrameRenderedListener activityAsListener = (OnFirstFrameRenderedListener) fragmentActivity;
+        activityAsListener.onFirstFrameRendered();
+      }
+    }
+  };
+
   public FlutterFragment() {
     // Ensure that we at least have an empty Bundle of arguments so that we don't
     // need to continually check for null arguments before grabbing one.
     setArguments(new Bundle());
   }
 
-  public void prepareForNavigation() {
-    flutterView.setAlpha(0.0f);
-  }
-
   /**
    * The {@link FlutterEngine} that backs the Flutter content presented by this {@code Fragment}.
    *
@@ -304,6 +316,7 @@ public class FlutterFragment extends Fragment {
   @Override
   public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
     flutterView = new FlutterView(getContext(), getRenderMode());
+    flutterView.addOnFirstFrameRenderedListener(onFirstFrameRenderedListener);
 
     // 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
@@ -433,6 +446,7 @@ public class FlutterFragment extends Fragment {
   public void onDestroyView() {
     super.onDestroyView();
     Log.d(TAG, "onDestroyView()");
+    flutterView.removeOnFirstFrameRenderedListener(onFirstFrameRenderedListener);
     flutterView.detachFromFlutterEngine();
   }
 
@@ -580,6 +594,16 @@ public class FlutterFragment extends Fragment {
       : getActivity();
   }
 
+  /**
+   * Invoked after the {@link FlutterView} within this {@code FlutterFragment} renders its first
+   * frame.
+   * <p>
+   * The owning {@code Activity} is also sent this message, if it implements
+   * {@link OnFirstFrameRenderedListener}. This method is invoked before the {@code Activity}'s
+   * version.
+   */
+  protected void onFirstFrameRendered() {}
+
   /**
    * Provides a {@link FlutterEngine} instance to be used by a {@code FlutterFragment}.
    * <p>

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

@@ -12,7 +12,11 @@ import android.util.Log;
 import android.view.SurfaceHolder;
 import android.view.SurfaceView;
 
+import java.util.HashSet;
+import java.util.Set;
+
 import io.flutter.embedding.engine.renderer.FlutterRenderer;
+import io.flutter.embedding.engine.renderer.OnFirstFrameRenderedListener;
 
 /**
  * Paints a Flutter UI on a {@link android.view.Surface}.
@@ -36,6 +40,8 @@ public class FlutterSurfaceView extends SurfaceView implements FlutterRenderer.R
   private boolean isAttachedToFlutterRenderer = false;
   @Nullable
   private FlutterRenderer flutterRenderer;
+  @NonNull
+  private Set<OnFirstFrameRenderedListener> onFirstFrameRenderedListeners = new HashSet<>();
 
   // Connects the {@code Surface} beneath this {@code SurfaceView} with Flutter's native code.
   // Callbacks are received by this Object and then those messages are forwarded to our
@@ -177,11 +183,33 @@ public class FlutterSurfaceView extends SurfaceView implements FlutterRenderer.R
     flutterRenderer.surfaceDestroyed();
   }
 
+  /**
+   * Adds the given {@code listener} to this {@code FlutterSurfaceView}, to be notified upon Flutter's
+   * first rendered frame.
+   */
+  @Override
+  public void addOnFirstFrameRenderedListener(@NonNull OnFirstFrameRenderedListener listener) {
+    onFirstFrameRenderedListeners.add(listener);
+  }
+
+  /**
+   * Removes the given {@code listener}, which was previously added with
+   * {@link #addOnFirstFrameRenderedListener(OnFirstFrameRenderedListener)}.
+   */
+  @Override
+  public void removeOnFirstFrameRenderedListener(@NonNull OnFirstFrameRenderedListener listener) {
+    onFirstFrameRenderedListeners.remove(listener);
+  }
+
   @Override
   public void onFirstFrameRendered() {
     // TODO(mattcarroll): decide where this method should live and what it needs to do.
     Log.d(TAG, "onFirstFrameRendered()");
     // Now that a frame is ready to display, take this SurfaceView from transparent to opaque.
     setAlpha(1.0f);
+
+    for (OnFirstFrameRenderedListener listener : onFirstFrameRenderedListeners) {
+      listener.onFirstFrameRendered();
+    }
   }
 }

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

@@ -13,7 +13,11 @@ import android.util.Log;
 import android.view.Surface;
 import android.view.TextureView;
 
+import java.util.HashSet;
+import java.util.Set;
+
 import io.flutter.embedding.engine.renderer.FlutterRenderer;
+import io.flutter.embedding.engine.renderer.OnFirstFrameRenderedListener;
 
 /**
  * Paints a Flutter UI on a {@link SurfaceTexture}.
@@ -37,6 +41,8 @@ public class FlutterTextureView extends TextureView implements FlutterRenderer.R
   private boolean isAttachedToFlutterRenderer = false;
   @Nullable
   private FlutterRenderer flutterRenderer;
+  @NonNull
+  private Set<OnFirstFrameRenderedListener> onFirstFrameRenderedListeners = new HashSet<>();
 
   // Connects the {@code SurfaceTexture} beneath this {@code TextureView} with Flutter's native code.
   // Callbacks are received by this Object and then those messages are forwarded to our
@@ -181,9 +187,31 @@ public class FlutterTextureView extends TextureView implements FlutterRenderer.R
     flutterRenderer.surfaceDestroyed();
   }
 
+  /**
+   * Adds the given {@code listener} to this {@code FlutterTextureView}, to be notified upon Flutter's
+   * first rendered frame.
+   */
+  @Override
+  public void addOnFirstFrameRenderedListener(@NonNull OnFirstFrameRenderedListener listener) {
+    onFirstFrameRenderedListeners.add(listener);
+  }
+
+  /**
+   * Removes the given {@code listener}, which was previously added with
+   * {@link #addOnFirstFrameRenderedListener(OnFirstFrameRenderedListener)}.
+   */
+  @Override
+  public void removeOnFirstFrameRenderedListener(@NonNull OnFirstFrameRenderedListener listener) {
+    onFirstFrameRenderedListeners.remove(listener);
+  }
+
   @Override
   public void onFirstFrameRendered() {
     // TODO(mattcarroll): decide where this method should live and what it needs to do.
     Log.d(TAG, "onFirstFrameRendered()");
+
+    for (OnFirstFrameRenderedListener listener : onFirstFrameRenderedListeners) {
+      listener.onFirstFrameRendered();
+    }
   }
 }

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

@@ -31,6 +31,7 @@ import java.util.Locale;
 
 import io.flutter.embedding.engine.FlutterEngine;
 import io.flutter.embedding.engine.renderer.FlutterRenderer;
+import io.flutter.embedding.engine.renderer.OnFirstFrameRenderedListener;
 import io.flutter.plugin.editing.TextInputPlugin;
 import io.flutter.view.AccessibilityBridge;
 
@@ -147,6 +148,22 @@ public class FlutterView extends FrameLayout {
     }
   }
 
+  /**
+   * Adds the given {@code listener} to this {@code FlutterView}, to be notified upon Flutter's
+   * first rendered frame.
+   */
+  public void addOnFirstFrameRenderedListener(@NonNull OnFirstFrameRenderedListener listener) {
+    renderSurface.addOnFirstFrameRenderedListener(listener);
+  }
+
+  /**
+   * Removes the given {@code listener}, which was previously added with
+   * {@link #addOnFirstFrameRenderedListener(OnFirstFrameRenderedListener)}.
+   */
+  public void removeOnFirstFrameRenderedListener(@NonNull OnFirstFrameRenderedListener listener) {
+    renderSurface.removeOnFirstFrameRenderedListener(listener);
+  }
+
   //------- Start: Process View configuration that Flutter cares about. ------
   /**
    * Sends relevant configuration data from Android to Flutter when the Android

shell/platform/android/io/flutter/embedding/engine/renderer/FlutterRenderer.java

@@ -267,6 +267,18 @@ public class FlutterRenderer implements TextureRegistry {
      * never be called.
      */
     void onFirstFrameRendered();
+
+    /**
+     * Adds the given {@code listener} to this {@code FlutterRenderer}, to be notified upon Flutter's
+     * first rendered frame.
+     */
+    void addOnFirstFrameRenderedListener(@NonNull OnFirstFrameRenderedListener listener);
+
+    /**
+     * Removes the given {@code listener}, which was previously added with
+     * {@link #addOnFirstFrameRenderedListener(OnFirstFrameRenderedListener)}.
+     */
+    void removeOnFirstFrameRenderedListener(@NonNull OnFirstFrameRenderedListener listener);
   }
 
   /**

shell/platform/android/io/flutter/view/FlutterNativeView.java

@@ -14,6 +14,7 @@ import io.flutter.embedding.engine.FlutterEngine.EngineLifecycleListener;
 import io.flutter.embedding.engine.dart.DartExecutor;
 import io.flutter.embedding.engine.renderer.FlutterRenderer;
 import io.flutter.embedding.engine.renderer.FlutterRenderer.RenderSurface;
+import io.flutter.embedding.engine.renderer.OnFirstFrameRenderedListener;
 import io.flutter.plugin.common.*;
 import java.nio.ByteBuffer;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -199,6 +200,12 @@ public class FlutterNativeView implements BinaryMessenger {
             }
             mFlutterView.onFirstFrame();
         }
+
+        @Override
+        public void addOnFirstFrameRenderedListener(@NonNull OnFirstFrameRenderedListener listener) {}
+
+        @Override
+        public void removeOnFirstFrameRenderedListener(@NonNull OnFirstFrameRenderedListener listener) {}
     }
 
     private final class EngineLifecycleListenerImpl implements EngineLifecycleListener {