Expose a hasRenderedFirstFrame() method in FlutterView (flutter#34275)…

…. (flutter#9285)

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

@@ -68,6 +68,7 @@ public class FlutterView extends FrameLayout {
   // Internal view hierarchy references.
   @Nullable
   private FlutterRenderer.RenderSurface renderSurface;
+  private boolean didRenderFirstFrame;
 
   // Connections to a Flutter execution context.
   @Nullable
@@ -97,6 +98,13 @@ public void onAccessibilityChanged(boolean isAccessibilityEnabled, boolean isTou
     }
   };
 
+  private final OnFirstFrameRenderedListener onFirstFrameRenderedListener = new OnFirstFrameRenderedListener() {
+    @Override
+    public void onFirstFrameRendered() {
+      didRenderFirstFrame = true;
+    }
+  };
+
   /**
    * Constructs a {@code FlutterView} programmatically, without any XML attributes.
    * <p>
@@ -171,11 +179,34 @@ private void init() {
         break;
     }
 
+    // Register a listener for the first frame render event to set didRenderFirstFrame.
+    renderSurface.addOnFirstFrameRenderedListener(onFirstFrameRenderedListener);
+
     // FlutterView needs to be focusable so that the InputMethodManager can interact with it.
     setFocusable(true);
     setFocusableInTouchMode(true);
   }
 
+  /**
+   * Returns true if an attached {@link FlutterEngine} has rendered at least 1 frame to this
+   * {@code FlutterView}.
+   * <p>
+   * Returns false if no {@link FlutterEngine} is attached.
+   * <p>
+   * This flag is specific to a given {@link FlutterEngine}. The following hypothetical timeline
+   * demonstrates how this flag changes over time.
+   * <ol>
+   *   <li>{@code flutterEngineA} is attached to this {@code FlutterView}: returns false</li>
+   *   <li>{@code flutterEngineA} renders its first frame to this {@code FlutterView}: returns true</li>
+   *   <li>{@code flutterEngineA} is detached from this {@code FlutterView}: returns false</li>
+   *   <li>{@code flutterEngineB} is attached to this {@code FlutterView}: returns false</li>
+   *   <li>{@code flutterEngineB} renders its first frame to this {@code FlutterView}: returns true</li>
+   * </ol>
+   */
+  public boolean hasRenderedFirstFrame() {
+    return didRenderFirstFrame;
+  }
+
   /**
    * Adds the given {@code listener} to this {@code FlutterView}, to be notified upon Flutter's
    * first rendered frame.
@@ -471,6 +502,7 @@ public void attachToFlutterEngine(@NonNull FlutterEngine flutterEngine) {
     this.flutterEngine = flutterEngine;
 
     // Instruct our FlutterRenderer that we are now its designated RenderSurface.
+    didRenderFirstFrame = false;
     this.flutterEngine.getRenderer().attachToRenderSurface(renderSurface);
 
     // Initialize various components that know how to process Android View I/O
@@ -536,6 +568,7 @@ public void detachFromFlutterEngine() {
     textInputPlugin.getInputMethodManager().restartInput(this);
 
     // Instruct our FlutterRenderer that we are no longer interested in being its RenderSurface.
+    didRenderFirstFrame = false;
     flutterEngine.getRenderer().detachFromRenderSurface();
     flutterEngine = null;