[SnackBar] Handle anchor view properly so no memory leak will happen

The anchor view can be detached even when the snack bar (or any
transient bottom bar) is showing. If this situation happens the
global layout listener it registers with the anchor view will
become not removable due to a bug/intended behavior of Android View's
implementation.

We need to remove the listener when the anchor view is detached to
fix the issue.

This CL also refactors the whole implementation of anchor view and consolidates
the anchoring/unanchoring logic to improve readability and robustness of it.

Resolves #2042

PiperOrigin-RevId: 382603130

Author: drchen

lib/java/com/google/android/material/snackbar/BaseTransientBottomBar.java

@@ -83,6 +83,7 @@
 import com.google.android.material.resources.MaterialResources;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
+import java.lang.ref.WeakReference;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -262,19 +263,11 @@ public boolean handleMessage(@NonNull Message message) {
 
   private int duration;
   private boolean gestureInsetBottomIgnored;
-  @Nullable private View anchorView;
+
+  @Nullable
+  private Anchor anchor;
+
   private boolean anchorViewLayoutListenerEnabled = false;
-  private final OnGlobalLayoutListener anchorViewLayoutListener =
-      new OnGlobalLayoutListener() {
-        @Override
-        public void onGlobalLayout() {
-          if (!anchorViewLayoutListenerEnabled) {
-            return;
-          }
-          extraBottomMarginAnchorView = calculateBottomMarginForAnchorView();
-          updateMargins();
-        }
-      };
 
   @RequiresApi(VERSION_CODES.Q)
   private final Runnable bottomMarginGestureInsetRunnable =
@@ -451,7 +444,7 @@ private void updateMargins() {
     }
 
     int extraBottomMargin =
-        anchorView != null ? extraBottomMarginAnchorView : extraBottomMarginWindowInset;
+        getAnchorView() != null ? extraBottomMarginAnchorView : extraBottomMarginWindowInset;
     MarginLayoutParams marginParams = (MarginLayoutParams) layoutParams;
     marginParams.bottomMargin = originalMargins.bottom + extraBottomMargin;
     marginParams.leftMargin = originalMargins.left + extraLeftMarginWindowInset;
@@ -566,15 +559,16 @@ public B setAnimationMode(@AnimationMode int animationMode) {
    */
   @Nullable
   public View getAnchorView() {
-    return anchorView;
+    return anchor == null ? null : anchor.getAnchorView();
   }
 
   /** Sets the view the {@link BaseTransientBottomBar} should be anchored above. */
   @NonNull
   public B setAnchorView(@Nullable View anchorView) {
-    ViewUtils.removeOnGlobalLayoutListener(this.anchorView, anchorViewLayoutListener);
-    this.anchorView = anchorView;
-    ViewUtils.addOnGlobalLayoutListener(this.anchorView, anchorViewLayoutListener);
+    if (this.anchor != null) {
+      this.anchor.unanchor();
+    }
+    this.anchor = anchorView == null ? null : Anchor.anchor(this, anchorView);
     return (B) this;
   }
 
@@ -768,8 +762,7 @@ public void run() {
         setUpBehavior((CoordinatorLayout.LayoutParams) lp);
       }
 
-      extraBottomMarginAnchorView = calculateBottomMarginForAnchorView();
-      updateMargins();
+      recalculateAndUpdateMargins();
 
       // Set view to INVISIBLE so it doesn't flash on the screen before the inset adjustment is
       // handled and the enter animation is started
@@ -861,18 +854,23 @@ public void onDragStateChanged(int state) {
     clp.setBehavior(behavior);
     // Also set the inset edge so that views can dodge the bar correctly, but only if there is
     // no anchor view.
-    if (anchorView == null) {
+    if (getAnchorView() == null) {
       clp.insetEdge = Gravity.BOTTOM;
     }
   }
 
+  private void recalculateAndUpdateMargins() {
+    extraBottomMarginAnchorView = calculateBottomMarginForAnchorView();
+    updateMargins();
+  }
+
   private int calculateBottomMarginForAnchorView() {
-    if (anchorView == null) {
+    if (getAnchorView() == null) {
       return 0;
     }
 
     int[] anchorViewLocation = new int[2];
-    anchorView.getLocationOnScreen(anchorViewLocation);
+    getAnchorView().getLocationOnScreen(anchorViewLocation);
     int anchorViewAbsoluteYTop = anchorViewLocation[1];
 
     int[] targetParentLocation = new int[2];
@@ -1096,9 +1094,6 @@ void onViewHidden(int event) {
       }
     }
 
-    // Reset anchor view and onGlobalLayoutListener so they won't be leaked.
-    setAnchorView(null);
-
     // Lastly, hide and remove the view from the parent (if attached)
     ViewParent parent = view.getParent();
     if (parent instanceof ViewGroup) {
@@ -1362,4 +1357,77 @@ public void onInterceptTouchEvent(
       }
     }
   }
+
+  @SuppressWarnings("rawtypes") // Generic type of BaseTransientBottomBar doesn't matter here.
+  static class Anchor
+      implements android.view.View.OnAttachStateChangeListener, OnGlobalLayoutListener {
+    @NonNull
+    private final WeakReference<BaseTransientBottomBar> transientBottomBar;
+
+    @NonNull
+    private final WeakReference<View> anchorView;
+
+    static Anchor anchor(
+        @NonNull BaseTransientBottomBar transientBottomBar, @NonNull View anchorView) {
+      Anchor anchor = new Anchor(transientBottomBar, anchorView);
+      if (ViewCompat.isAttachedToWindow(anchorView)) {
+        ViewUtils.addOnGlobalLayoutListener(anchorView, anchor);
+      }
+      anchorView.addOnAttachStateChangeListener(anchor);
+      return anchor;
+    }
+
+    private Anchor(
+        @NonNull BaseTransientBottomBar transientBottomBar, @NonNull View anchorView) {
+      this.transientBottomBar = new WeakReference<>(transientBottomBar);
+      this.anchorView = new WeakReference<>(anchorView);
+    }
+
+    @Override
+    public void onViewAttachedToWindow(View anchorView) {
+      if (unanchorIfNoTransientBottomBar()) {
+        return;
+      }
+      ViewUtils.addOnGlobalLayoutListener(anchorView, this);
+    }
+
+    @Override
+    public void onViewDetachedFromWindow(View anchorView) {
+      if (unanchorIfNoTransientBottomBar()) {
+        return;
+      }
+      ViewUtils.removeOnGlobalLayoutListener(anchorView, this);
+    }
+
+    @Override
+    public void onGlobalLayout() {
+      if (unanchorIfNoTransientBottomBar()
+          || !transientBottomBar.get().anchorViewLayoutListenerEnabled) {
+        return;
+      }
+      transientBottomBar.get().recalculateAndUpdateMargins();
+    }
+
+    @Nullable
+    View getAnchorView() {
+      return anchorView.get();
+    }
+
+    private boolean unanchorIfNoTransientBottomBar() {
+      if (transientBottomBar.get() == null) {
+        unanchor();
+        return true;
+      }
+      return false;
+    }
+
+    void unanchor() {
+      if (anchorView.get() != null) {
+        anchorView.get().removeOnAttachStateChangeListener(this);
+        ViewUtils.removeOnGlobalLayoutListener(anchorView.get(), this);
+      }
+      anchorView.clear();
+      transientBottomBar.clear();
+    }
+  }
 }