[wm] Add APIs to notify task focused & task focus lost

- Let listeners know which task is going to front or back.

 onTaskFocusChanged(taskId, focused)
- calls when the task gets or loses focus.

Test: atest ActivityStackSupervisorTest#testNotifyTaskFocusChanged
Bug: 129951708
Change-Id: I92bfdb760f4c5f1db00334f4eff41fe52115b942

core/java/android/app/ITaskStackListener.aidl

@@ -204,4 +204,12 @@ oneway interface ITaskStackListener {
      * @param frozen if true, Recents Tasks list is currently frozen, false otherwise
      */
     void onRecentTaskListFrozenChanged(boolean frozen);
+
+    /**
+     * Called when a task gets or loses focus.
+     *
+     * @param taskId id of the task.
+     * @param {@code true} if the task got focus, {@code false} if it lost it.
+     */
+    void onTaskFocusChanged(int taskId, boolean focused);
 }

core/java/android/app/TaskStackListener.java

@@ -199,4 +199,8 @@ public abstract class TaskStackListener extends ITaskStackListener.Stub {
     @Override
     public void onRecentTaskListFrozenChanged(boolean frozen) {
     }
+
+    @Override
+    public void onTaskFocusChanged(int taskId, boolean focused) {
+    }
 }

services/core/java/com/android/server/wm/ActivityTaskManagerService.java

@@ -5554,11 +5554,20 @@ public class ActivityTaskManagerService extends IActivityTaskManager.Stub {
         if (mLastResumedActivity != null && r.mUserId != mLastResumedActivity.mUserId) {
             mAmInternal.sendForegroundProfileChanged(r.mUserId);
         }
+        final Task prevTask = mLastResumedActivity != null ? mLastResumedActivity.getTask() : null;
+
         updateResumedAppTrace(r);
         mLastResumedActivity = r;
 
         r.getDisplay().setFocusedApp(r, true);
 
+        if (prevTask == null || task != prevTask) {
+            if (prevTask != null) {
+                mTaskChangeNotificationController.notifyTaskFocusChanged(prevTask.mTaskId, false);
+            }
+            mTaskChangeNotificationController.notifyTaskFocusChanged(task.mTaskId, true);
+        }
+
         applyUpdateLockStateLocked(r);
         applyUpdateVrModeLocked(r);
 

services/core/java/com/android/server/wm/TaskChangeNotificationController.java

@@ -59,6 +59,7 @@ class TaskChangeNotificationController {
     private static final int NOTIFY_TASK_LIST_UPDATED_LISTENERS_MSG = 24;
     private static final int NOTIFY_SINGLE_TASK_DISPLAY_EMPTY = 25;
     private static final int NOTIFY_TASK_LIST_FROZEN_UNFROZEN_MSG = 26;
+    private static final int NOTIFY_TASK_FOCUS_CHANGED_MSG = 27;
 
     // Delay in notifying task stack change listeners (in millis)
     private static final int NOTIFY_TASK_STACK_CHANGE_LISTENERS_DELAY = 100;
@@ -179,6 +180,10 @@ class TaskChangeNotificationController {
         l.onRecentTaskListFrozenChanged(m.arg1 != 0);
     };
 
+    private final TaskStackConsumer mNotifyTaskFocusChanged = (l, m) -> {
+        l.onTaskFocusChanged(m.arg1, m.arg2 != 0);
+    };
+
     @FunctionalInterface
     public interface TaskStackConsumer {
         void accept(ITaskStackListener t, Message m) throws RemoteException;
@@ -273,6 +278,9 @@ class TaskChangeNotificationController {
                 case NOTIFY_TASK_LIST_FROZEN_UNFROZEN_MSG:
                     forAllRemoteListeners(mNotifyTaskListFrozen, msg);
                     break;
+                case NOTIFY_TASK_FOCUS_CHANGED_MSG:
+                    forAllRemoteListeners(mNotifyTaskFocusChanged, msg);
+                    break;
             }
         }
     }
@@ -565,4 +573,12 @@ class TaskChangeNotificationController {
         forAllLocalListeners(mNotifyTaskListFrozen, msg);
         msg.sendToTarget();
     }
+
+    /** @see ITaskStackListener#onTaskFocusChanged(int, boolean) */
+    void notifyTaskFocusChanged(int taskId, boolean focused) {
+        final Message msg = mHandler.obtainMessage(NOTIFY_TASK_FOCUS_CHANGED_MSG,
+                taskId, focused ? 1 : 0);
+        forAllLocalListeners(mNotifyTaskFocusChanged, msg);
+        msg.sendToTarget();
+    }
 }

services/tests/wmtests/src/com/android/server/wm/ActivityStackSupervisorTests.java

@@ -144,4 +144,33 @@ public class ActivityStackSupervisorTests extends ActivityTestsBase {
                 anyInt() /* reason */, anyString() /* packageName */);
         verify(taskChangeNotifier, never()).notifyActivityDismissingDockedStack();
     }
+
+    /**
+     * Ensures that notify focus task changes.
+     */
+    @Test
+    public void testNotifyTaskFocusChanged() {
+        final ActivityRecord fullScreenActivityA = new ActivityBuilder(mService).setCreateTask(true)
+                .setStack(mFullscreenStack).build();
+        final Task taskA = fullScreenActivityA.getTask();
+
+        final TaskChangeNotificationController taskChangeNotifier =
+                mService.getTaskChangeNotificationController();
+        spyOn(taskChangeNotifier);
+
+        mService.setResumedActivityUncheckLocked(fullScreenActivityA, "resumeA");
+        verify(taskChangeNotifier).notifyTaskFocusChanged(eq(taskA.mTaskId) /* taskId */,
+                eq(true) /* focused */);
+        reset(taskChangeNotifier);
+
+        final ActivityRecord fullScreenActivityB = new ActivityBuilder(mService).setCreateTask(true)
+                .setStack(mFullscreenStack).build();
+        final Task taskB = fullScreenActivityB.getTask();
+
+        mService.setResumedActivityUncheckLocked(fullScreenActivityB, "resumeB");
+        verify(taskChangeNotifier).notifyTaskFocusChanged(eq(taskA.mTaskId) /* taskId */,
+                eq(false) /* focused */);
+        verify(taskChangeNotifier).notifyTaskFocusChanged(eq(taskB.mTaskId) /* taskId */,
+                eq(true) /* focused */);
+    }
 }