[Carousel] Changed Maskable.add/removeOnMaskChangedListener to Maskable.setOnMaskChangedListener.

This change is to prevent the case of items in a RecyclerView.Adapter being recycled and re-bound and having more and more listeners added to a MaskableFrameLayout.

PiperOrigin-RevId: 515048125

Author: hunterstich

docs/components/Carousel.md

@@ -88,7 +88,7 @@ The main means of changing the look of carousel is by setting the height of your
 If your `RecyclerView`'s item layout contains text or other content that needs to react to changes in the item's mask, you can listen for changes in mask size by setting an `onMaskChangedListener` on your `MaskableFrameLayout` inside your `RecyclerView.ViewHolder`.
 
 ```kotlin
-(viewHolder.itemView as MaskableFrameLayout).addOnMaskChangedListener(
+(viewHolder.itemView as MaskableFrameLayout).setOnMaskChangedListener(
     maskRect ->
       // Any custom motion to run when mask size changes
       viewHolder.title.setTranslationX(maskRect.left);

lib/java/com/google/android/material/carousel/Maskable.java

@@ -20,10 +20,9 @@
 import android.view.View;
 import androidx.annotation.FloatRange;
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 
-/**
- * Interface for any view that can clip itself and all children to a percentage of its size.
- */
+/** Interface for any view that can clip itself and all children to a percentage of its size. */
 interface Maskable {
 
   /**
@@ -45,9 +44,11 @@ interface Maskable {
   @NonNull
   RectF getMaskRectF();
 
-  /** Adds an {@link OnMaskChangedListener}. */
-  void addOnMaskChangedListener(@NonNull OnMaskChangedListener listener);
-
-  /** Removes an {@link OnMaskChangedListener}. */
-  void removeOnMaskChangedListener(@NonNull OnMaskChangedListener listener);
+  /**
+   * Sets an {@link OnMaskChangedListener}.
+   *
+   * @param listener a listener to receive callbacks for changes in the mask or null to clear the
+   *     listener.
+   */
+  void setOnMaskChangedListener(@Nullable OnMaskChangedListener listener);
 }

lib/java/com/google/android/material/carousel/MaskableFrameLayout.java

@@ -36,8 +36,6 @@
 import androidx.core.math.MathUtils;
 import com.google.android.material.animation.AnimationUtils;
 import com.google.android.material.shape.ShapeAppearanceModel;
-import java.util.ArrayList;
-import java.util.List;
 
 /** A {@link FrameLayout} than is able to mask itself and all children. */
 public class MaskableFrameLayout extends FrameLayout implements Maskable {
@@ -46,7 +44,7 @@ public class MaskableFrameLayout extends FrameLayout implements Maskable {
   private final RectF maskRect = new RectF();
   private final Path maskPath = new Path();
 
-  private final List<OnMaskChangedListener> onMaskChangedListeners = new ArrayList<>();
+  @Nullable private OnMaskChangedListener onMaskChangedListener;
 
   private final ShapeAppearanceModel shapeAppearanceModel;
 
@@ -105,13 +103,8 @@ public RectF getMaskRectF() {
   }
 
   @Override
-  public void addOnMaskChangedListener(@NonNull OnMaskChangedListener listener) {
-    onMaskChangedListeners.add(listener);
-  }
-
-  @Override
-  public void removeOnMaskChangedListener(@NonNull OnMaskChangedListener listener) {
-    onMaskChangedListeners.remove(listener);
+  public void setOnMaskChangedListener(@Nullable OnMaskChangedListener onMaskChangedListener) {
+    this.onMaskChangedListener = onMaskChangedListener;
   }
 
   private void onMaskChanged() {
@@ -122,8 +115,8 @@ private void onMaskChanged() {
     // masked away.
     float maskWidth = AnimationUtils.lerp(0f, getWidth() / 2F, 0f, 1f, maskXPercentage);
     maskRect.set(maskWidth, 0F, (getWidth() - maskWidth), getHeight());
-    for (OnMaskChangedListener listener : onMaskChangedListeners) {
-      listener.onMaskChanged(maskRect);
+    if (onMaskChangedListener != null) {
+      onMaskChangedListener.onMaskChanged(maskRect);
     }
     refreshMaskPath();
   }

lib/javatests/com/google/android/material/carousel/MaskableFrameLayoutTest.java

@@ -43,7 +43,7 @@ public class MaskableFrameLayoutTest {
   @Test
   public void testSetMaskXPercentage_shouldTriggerMaskChangedListeners() {
     MaskableFrameLayout maskableFrameLayout = createMaskableFrameLayoutWithSize(100, 100);
-    maskableFrameLayout.addOnMaskChangedListener(listener);
+    maskableFrameLayout.setOnMaskChangedListener(listener);
 
     maskableFrameLayout.setMaskXPercentage(.5F);