Call onBackCancelled() when an active callback is removed from the WindowOnBackInvokedDispatcher

When an OnBackInvokedCallback is unregistered from a WindowOnBackInvokedDispatcher, it is important to check if the callback is the current top one and if the back animation is in progress. If it is, we should call onBackCancelled() on the callback as a final step.

Test: atest WindowOnBackInvokedDispatcherTest
Bug: 276816667
Change-Id: Icaf98899c474c4e8d89d4a9c77acc309d37e9582

core/java/android/window/BackProgressAnimator.java

@@ -43,7 +43,7 @@ public class BackProgressAnimator {
     private ProgressCallback mCallback;
     private float mProgress = 0;
     private BackMotionEvent mLastBackEvent;
-    private boolean mStarted = false;
+    private boolean mBackAnimationInProgress = false;
 
     private void setProgress(float progress) {
         mProgress = progress;
@@ -87,7 +87,7 @@ public class BackProgressAnimator {
      * @param event the {@link BackMotionEvent} containing the latest target progress.
      */
     public void onBackProgressed(BackMotionEvent event) {
-        if (!mStarted) {
+        if (!mBackAnimationInProgress) {
             return;
         }
         mLastBackEvent = event;
@@ -108,7 +108,7 @@ public class BackProgressAnimator {
         reset();
         mLastBackEvent = event;
         mCallback = callback;
-        mStarted = true;
+        mBackAnimationInProgress = true;
     }
 
     /**
@@ -122,7 +122,7 @@ public class BackProgressAnimator {
             // Should never happen.
             mSpring.cancel();
         }
-        mStarted = false;
+        mBackAnimationInProgress = false;
         mLastBackEvent = null;
         mCallback = null;
         mProgress = 0;
@@ -149,8 +149,13 @@ public class BackProgressAnimator {
         mSpring.animateToFinalPosition(0);
     }
 
+    /** Returns true if the back animation is in progress. */
+    boolean isBackAnimationInProgress() {
+        return mBackAnimationInProgress;
+    }
+
     private void updateProgressValue(float progress) {
-        if (mLastBackEvent == null || mCallback == null || !mStarted) {
+        if (mLastBackEvent == null || mCallback == null || !mBackAnimationInProgress) {
             return;
         }
         mCallback.onProgressUpdate(

core/java/android/window/WindowOnBackInvokedDispatcher.java

@@ -158,6 +158,16 @@ public class WindowOnBackInvokedDispatcher implements OnBackInvokedDispatcher {
         mAllCallbacks.remove(callback);
         // Re-populate the top callback to WM if the removed callback was previously the top one.
         if (previousTopCallback == callback) {
+            // We should call onBackCancelled() when an active callback is removed from dispatcher.
+            if (mProgressAnimator.isBackAnimationInProgress()
+                    && callback instanceof OnBackAnimationCallback) {
+                // The ProgressAnimator will handle the new topCallback, so we don't want to call
+                // onBackCancelled() on it. We call immediately the callback instead.
+                OnBackAnimationCallback animatedCallback = (OnBackAnimationCallback) callback;
+                animatedCallback.onBackCancelled();
+                Log.d(TAG, "The callback was removed while a back animation was in progress, "
+                        + "an onBackCancelled() was dispatched.");
+            }
             setTopOnBackInvokedCallback(getTopCallback());
         }
     }

core/tests/coretests/src/android/window/WindowOnBackInvokedDispatcherTest.java

@@ -173,4 +173,25 @@ public class WindowOnBackInvokedDispatcherTest {
         waitForIdle();
         verify(mCallback2).onBackStarted(any(BackEvent.class));
     }
+
+    @Test
+    public void onUnregisterWhileBackInProgress_callOnBackCancelled() throws RemoteException {
+        ArgumentCaptor<OnBackInvokedCallbackInfo> captor =
+                ArgumentCaptor.forClass(OnBackInvokedCallbackInfo.class);
+
+        mDispatcher.registerOnBackInvokedCallback(
+                OnBackInvokedDispatcher.PRIORITY_DEFAULT, mCallback1);
+
+        verify(mWindowSession).setOnBackInvokedCallbackInfo(
+                Mockito.eq(mWindow),
+                captor.capture());
+        IOnBackInvokedCallback iOnBackInvokedCallback = captor.getValue().getCallback();
+        iOnBackInvokedCallback.onBackStarted(mBackEvent);
+        waitForIdle();
+        verify(mCallback1).onBackStarted(any(BackEvent.class));
+
+        mDispatcher.unregisterOnBackInvokedCallback(mCallback1);
+        verify(mCallback1).onBackCancelled();
+        verifyNoMoreInteractions(mCallback1);
+    }
 }