Add support for listening to AspectRatioFrameLayout's aspect ratio update

Currently, AspectRatioFrameLayout may need to resize itself if it could not
satisfy a target aspect ratio. User may want to know when this happen, or
whether this can happen, so they can update their UI accordingly. For
example: show/hide a button to toggle different resize mode only when the
aspect ratio of the view and the content is very different.

GitHub: #3736

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=187484241

RELEASENOTES.md

@@ -2,6 +2,9 @@
 
 ### dev-v2 (not yet released) ###
 
+* UI components:
+  * Add support for listening to `AspectRatioFrameLayout`'s aspect ratio update
+    ([#3736](https://github.com/google/ExoPlayer/issues/3736)).
 * Gradle: Replace 'compile' configuration (deprecated) with 'implementation' and
   'api'. Note: This may lead to build breakage for applications upgrading from
   previous version that rely on indirect dependency for certain modules. In such

library/ui/src/main/java/com/google/android/exoplayer2/ui/AspectRatioFrameLayout.java

@@ -28,6 +28,22 @@ import java.lang.annotation.RetentionPolicy;
  */
 public final class AspectRatioFrameLayout extends FrameLayout {
 
+  /** Listener to be notified about changes of the aspect ratios of this view. */
+  public interface AspectRatioListener {
+
+    /**
+     * Called when either the target aspect ratio or the view aspect ratio is updated.
+     *
+     * @param targetAspectRatio The aspect ratio that has been set in {@link #setAspectRatio(float)}
+     * @param naturalAspectRatio The natural aspect ratio of this view (before its width and height
+     *     are modified to satisfy the target aspect ratio).
+     * @param aspectRatioMismatch Whether the target and natural aspect ratios differ enough for
+     *     changing the resize mode to have an effect.
+     */
+    void onAspectRatioUpdated(
+        float targetAspectRatio, float naturalAspectRatio, boolean aspectRatioMismatch);
+  }
+
   // LINT.IfChange
   /** Resize modes for {@link AspectRatioFrameLayout}. */
   @Retention(RetentionPolicy.SOURCE)
@@ -73,8 +89,12 @@ public final class AspectRatioFrameLayout extends FrameLayout {
    */
   private static final float MAX_ASPECT_RATIO_DEFORMATION_FRACTION = 0.01f;
 
+  private final AspectRatioUpdateDispatcher aspectRatioUpdateDispatcher;
+
+  private AspectRatioListener aspectRatioListener;
+
   private float videoAspectRatio;
-  private int resizeMode;
+  private @ResizeMode int resizeMode;
 
   public AspectRatioFrameLayout(Context context) {
     this(context, null);
@@ -92,6 +112,7 @@ public final class AspectRatioFrameLayout extends FrameLayout {
         a.recycle();
       }
     }
+    aspectRatioUpdateDispatcher = new AspectRatioUpdateDispatcher();
   }
 
   /**
@@ -107,6 +128,15 @@ public final class AspectRatioFrameLayout extends FrameLayout {
   }
 
   /**
+   * Sets the {@link AspectRatioListener}.
+   *
+   * @param listener The listener to be notified about aspect ratios changes.
+   */
+  public void setAspectRatioListener(AspectRatioListener listener) {
+    this.aspectRatioListener = listener;
+  }
+
+  /**
    * Returns the resize mode.
    */
   public @ResizeMode int getResizeMode() {
@@ -128,7 +158,7 @@ public final class AspectRatioFrameLayout extends FrameLayout {
   @Override
   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
     super.onMeasure(widthMeasureSpec, heightMeasureSpec);
-    if (resizeMode == RESIZE_MODE_FILL || videoAspectRatio <= 0) {
+    if (videoAspectRatio <= 0) {
       // Aspect ratio not set.
       return;
     }
@@ -139,6 +169,7 @@ public final class AspectRatioFrameLayout extends FrameLayout {
     float aspectDeformation = videoAspectRatio / viewAspectRatio - 1;
     if (Math.abs(aspectDeformation) <= MAX_ASPECT_RATIO_DEFORMATION_FRACTION) {
       // We're within the allowed tolerance.
+      aspectRatioUpdateDispatcher.scheduleUpdate(videoAspectRatio, viewAspectRatio, false);
       return;
     }
 
@@ -156,16 +187,51 @@ public final class AspectRatioFrameLayout extends FrameLayout {
           height = (int) (width / videoAspectRatio);
         }
         break;
-      default:
+      case RESIZE_MODE_FIT:
         if (aspectDeformation > 0) {
           height = (int) (width / videoAspectRatio);
         } else {
           width = (int) (height * videoAspectRatio);
         }
         break;
+      case RESIZE_MODE_FILL:
+      default:
+        // Ignore target aspect ratio
+        break;
     }
+    aspectRatioUpdateDispatcher.scheduleUpdate(videoAspectRatio, viewAspectRatio, true);
     super.onMeasure(MeasureSpec.makeMeasureSpec(width, MeasureSpec.EXACTLY),
         MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY));
   }
 
+  /** Dispatches updates to {@link AspectRatioListener}. */
+  private final class AspectRatioUpdateDispatcher implements Runnable {
+
+    private float targetAspectRatio;
+    private float naturalAspectRatio;
+    private boolean aspectRatioMismatch;
+    private boolean isScheduled;
+
+    public void scheduleUpdate(
+        float targetAspectRatio, float naturalAspectRatio, boolean aspectRatioMismatch) {
+      this.targetAspectRatio = targetAspectRatio;
+      this.naturalAspectRatio = naturalAspectRatio;
+      this.aspectRatioMismatch = aspectRatioMismatch;
+
+      if (!isScheduled) {
+        isScheduled = true;
+        post(this);
+      }
+    }
+
+    @Override
+    public void run() {
+      isScheduled = false;
+      if (aspectRatioListener == null) {
+        return;
+      }
+      aspectRatioListener.onAspectRatioUpdated(
+          targetAspectRatio, naturalAspectRatio, aspectRatioMismatch);
+    }
+  }
 }

library/ui/src/main/java/com/google/android/exoplayer2/ui/PlayerView.java

@@ -478,6 +478,12 @@ public class PlayerView extends FrameLayout {
     contentFrame.setResizeMode(resizeMode);
   }
 
+  /** Returns the resize mode. */
+  public @ResizeMode int getResizeMode() {
+    Assertions.checkState(contentFrame != null);
+    return contentFrame.getResizeMode();
+  }
+
   /** Returns whether artwork is displayed if present in the media. */
   public boolean getUseArtwork() {
     return useArtwork;
@@ -751,6 +757,17 @@ public class PlayerView extends FrameLayout {
   }
 
   /**
+   * Set the {@link AspectRatioFrameLayout.AspectRatioListener}.
+   *
+   * @param listener The listener to be notified about aspect ratios changes of the video content or
+   *     the content frame.
+   */
+  public void setAspectRatioListener(AspectRatioFrameLayout.AspectRatioListener listener) {
+    Assertions.checkState(contentFrame != null);
+    contentFrame.setAspectRatioListener(listener);
+  }
+
+  /**
    * Gets the view onto which video is rendered. This is a:
    *
    * <ul>