Ignore back invoke when window focus has lost

The back invoke target could lost focus during back navigation.
To prevent the non-focused window could still trigger back action cause
some unexpected behavior, this CL will listen focus changed and skip the
back invoke call.

Test: launch a trampoline activity and trigger back before next activity
shown.
Test: atest WindowOnBackInvokedDispatcherTest
Bug: 238050065

Change-Id: Ifd345b2283c5d07628e2884db6e4e13f3ec31e83

core/java/android/view/ViewRootImpl.java

@@ -3759,6 +3759,7 @@ public final class ViewRootImpl implements ViewParent,
             }
         }
         mFirstInputStage.onWindowFocusChanged(hasWindowFocus);
+        mOnBackInvokedDispatcher.onWindowFocusChanged(hasWindowFocus);
 
         // NOTE: there's no view visibility (appeared / disapparead) events when the windows focus
         // is lost, so we don't need to to force a flush - there might be other events such as

core/java/android/window/ImeOnBackInvokedDispatcher.java

@@ -81,8 +81,10 @@ public class ImeOnBackInvokedDispatcher implements OnBackInvokedDispatcher, Parc
             @OnBackInvokedDispatcher.Priority int priority,
             @NonNull OnBackInvokedCallback callback) {
         final Bundle bundle = new Bundle();
+        // Always invoke back for ime without checking the window focus.
         final IOnBackInvokedCallback iCallback =
-                new WindowOnBackInvokedDispatcher.OnBackInvokedCallbackWrapper(callback);
+                new WindowOnBackInvokedDispatcher.OnBackInvokedCallbackWrapper(callback,
+                        () -> true);
         bundle.putBinder(RESULT_KEY_CALLBACK, iCallback.asBinder());
         bundle.putInt(RESULT_KEY_PRIORITY, priority);
         bundle.putInt(RESULT_KEY_ID, callback.hashCode());

core/java/android/window/WindowOnBackInvokedDispatcher.java

@@ -32,6 +32,7 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.Objects;
 import java.util.TreeMap;
+import java.util.function.Supplier;
 
 /**
  * Provides window based implementation of {@link OnBackInvokedDispatcher}.
@@ -64,6 +65,7 @@ public class WindowOnBackInvokedDispatcher implements OnBackInvokedDispatcher {
     private final TreeMap<Integer, ArrayList<OnBackInvokedCallback>>
             mOnBackInvokedCallbacks = new TreeMap<>();
     private final Checker mChecker;
+    private boolean mHasFocus;
 
     public WindowOnBackInvokedDispatcher(boolean applicationCallBackEnabled) {
         mChecker = new Checker(applicationCallBackEnabled);
@@ -189,7 +191,7 @@ public class WindowOnBackInvokedDispatcher implements OnBackInvokedDispatcher {
                                     .ImeOnBackInvokedCallback
                                 ? ((ImeOnBackInvokedDispatcher.ImeOnBackInvokedCallback)
                                         callback).getIOnBackInvokedCallback()
-                                : new OnBackInvokedCallbackWrapper(callback);
+                                : new OnBackInvokedCallbackWrapper(callback, this::hasFocus);
                 callbackInfo = new OnBackInvokedCallbackInfo(iCallback, priority);
             }
             mWindowSession.setOnBackInvokedCallbackInfo(mWindow, callbackInfo);
@@ -198,6 +200,17 @@ public class WindowOnBackInvokedDispatcher implements OnBackInvokedDispatcher {
         }
     }
 
+    /**
+     * Called when window focus changed.
+     */
+    public void onWindowFocusChanged(boolean hasFocus) {
+        mHasFocus = hasFocus;
+    }
+
+    private boolean hasFocus() {
+        return mHasFocus;
+    }
+
     public OnBackInvokedCallback getTopCallback() {
         if (mAllCallbacks.isEmpty()) {
             return null;
@@ -221,9 +234,11 @@ public class WindowOnBackInvokedDispatcher implements OnBackInvokedDispatcher {
 
     static class OnBackInvokedCallbackWrapper extends IOnBackInvokedCallback.Stub {
         private final WeakReference<OnBackInvokedCallback> mCallback;
-
-        OnBackInvokedCallbackWrapper(@NonNull OnBackInvokedCallback callback) {
+        private final Supplier<Boolean> mHasFocus;
+        OnBackInvokedCallbackWrapper(@NonNull OnBackInvokedCallback callback,
+                @NonNull Supplier<Boolean> hasFocus) {
             mCallback = new WeakReference<>(callback);
+            mHasFocus = hasFocus;
         }
 
         @Override
@@ -263,7 +278,10 @@ public class WindowOnBackInvokedDispatcher implements OnBackInvokedDispatcher {
                 if (callback == null) {
                     return;
                 }
-
+                if (!mHasFocus.get()) {
+                    Log.w(TAG, "Skip back invoke due to current focus has lost.");
+                    return;
+                }
                 callback.onBackInvoked();
             });
         }

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

@@ -66,6 +66,7 @@ public class WindowOnBackInvokedDispatcherTest {
         MockitoAnnotations.initMocks(this);
         mDispatcher = new WindowOnBackInvokedDispatcher(true /* applicationCallbackEnabled */);
         mDispatcher.attachToWindow(mWindowSession, mWindow);
+        mDispatcher.onWindowFocusChanged(true);
     }
 
     private void waitForIdle() {
@@ -152,4 +153,31 @@ public class WindowOnBackInvokedDispatcherTest {
         waitForIdle();
         verify(mCallback2).onBackStarted();
     }
+
+    @Test
+    public void skipBackInvokeWhenNoFocus() throws RemoteException {
+        ArgumentCaptor<OnBackInvokedCallbackInfo> captor =
+                ArgumentCaptor.forClass(OnBackInvokedCallbackInfo.class);
+
+        mDispatcher.registerOnBackInvokedCallback(
+                OnBackInvokedDispatcher.PRIORITY_DEFAULT, mCallback1);
+
+        verify(mWindowSession, times(1)).setOnBackInvokedCallbackInfo(
+                Mockito.eq(mWindow),
+                captor.capture());
+
+        verify(mWindowSession).setOnBackInvokedCallbackInfo(Mockito.eq(mWindow), captor.capture());
+
+        // Should invoke back if it's still in focused.
+        captor.getValue().getCallback().onBackInvoked();
+        waitForIdle();
+        verify(mCallback1).onBackInvoked();
+
+        // In case the focus has lost during back gesture.
+        mDispatcher.onWindowFocusChanged(false);
+
+        captor.getValue().getCallback().onBackInvoked();
+        waitForIdle();
+        verifyZeroInteractions(mCallback1);
+    }
 }