Ensure ActivityStack's cached resumed activity is updated.

ActivityStack stores a reference to its resumed activity for quicker
future reference. Currently, children must inform the ActivityStack
of any movement in order to properly set this value. We are missing
cases today, causing stale values to persist.

This changelist addresses by updating the stack's paused and resumed
activity references whenever the ancestor stack changes when a task
or activity's parent is changed.

Change-Id: I5ef6db6af3d7e304012c54afa996fbfff28e9110
Fixes: 75992227
Test: atest FrameworksServicesTests:com.android.server.am.ActivityStackTests#testResumedActivityFromActivityReparenting
Test: atest FrameworksServicesTests:com.android.server.am.ActivityStackTests#testPrimarySplitScreenToFullscreenWhenMovedToBack
Test: atest CtsActivityManagerDeviceTestCases:ActivityManagerPinnedStackTests#testFinishPipActivityWithTaskOverlay
diff --git a/services/core/java/com/android/server/am/ActivityRecord.java b/services/core/java/com/android/server/am/ActivityRecord.java
index e539bf8..3eff8c4 100644
--- a/services/core/java/com/android/server/am/ActivityRecord.java
+++ b/services/core/java/com/android/server/am/ActivityRecord.java
@@ -779,11 +779,13 @@
      * @param task The new parent {@link TaskRecord}.
      */
     void setTask(TaskRecord task) {
-        setTask(task, false /*reparenting*/);
+        setTask(task /* task */, false /* reparenting */);
     }
 
     /**
      * This method should only be called by {@link TaskRecord#removeActivity(ActivityRecord)}.
+     * @param task          The new parent task.
+     * @param reparenting   Whether we're in the middle of reparenting.
      */
     void setTask(TaskRecord task, boolean reparenting) {
         // Do nothing if the {@link TaskRecord} is the same as the current {@link getTask}.
@@ -791,12 +793,19 @@
             return;
         }
 
-        final ActivityStack stack = getStack();
+        final ActivityStack oldStack = getStack();
+        final ActivityStack newStack = task != null ? task.getStack() : null;
 
-        // If the new {@link TaskRecord} is from a different {@link ActivityStack}, remove this
-        // {@link ActivityRecord} from its current {@link ActivityStack}.
-        if (!reparenting && stack != null && (task == null || stack != task.getStack())) {
-            stack.onActivityRemovedFromStack(this);
+        // Inform old stack (if present) of activity removal and new stack (if set) of activity
+        // addition.
+        if (oldStack != newStack) {
+            if (!reparenting && oldStack != null) {
+                oldStack.onActivityRemovedFromStack(this);
+            }
+
+            if (newStack != null) {
+                newStack.onActivityAddedToStack(this);
+            }
         }
 
         this.task = task;
@@ -1073,8 +1082,15 @@
         // Must reparent first in window manager
         mWindowContainerController.reparent(newTask.getWindowContainerController(), position);
 
+        // Reparenting prevents informing the parent stack of activity removal in the case that
+        // the new stack has the same parent. we must manually signal here if this is not the case.
+        final ActivityStack prevStack = prevTask.getStack();
+
+        if (prevStack != newTask.getStack()) {
+            prevStack.onActivityRemovedFromStack(this);
+        }
         // Remove the activity from the old task and add it to the new task.
-        prevTask.removeActivity(this, true /*reparenting*/);
+        prevTask.removeActivity(this, true /* reparenting */);
 
         newTask.addActivityAtIndex(position, this);
     }
diff --git a/services/core/java/com/android/server/am/ActivityStack.java b/services/core/java/com/android/server/am/ActivityStack.java
index 649d577..8bbd7b4 100644
--- a/services/core/java/com/android/server/am/ActivityStack.java
+++ b/services/core/java/com/android/server/am/ActivityStack.java
@@ -489,13 +489,13 @@
      */
     void onActivityStateChanged(ActivityRecord record, ActivityState state, String reason) {
         if (record == mResumedActivity && state != RESUMED) {
-            clearResumedActivity(reason + " - onActivityStateChanged");
+            setResumedActivity(null, reason + " - onActivityStateChanged");
         }
 
         if (state == RESUMED) {
             if (DEBUG_STACK) Slog.v(TAG_STACK, "set resumed activity to:" + record + " reason:"
                     + reason);
-            mResumedActivity = record;
+            setResumedActivity(record, reason + " - onActivityStateChanged");
             mService.setResumedActivityUncheckLocked(record, reason);
             mStackSupervisor.mRecentTasks.add(record.getTask());
         }
@@ -2314,14 +2314,14 @@
         return mResumedActivity;
     }
 
-    /**
-     * Clears reference to currently resumed activity.
-     */
-    private void clearResumedActivity(String reason) {
-        if (DEBUG_STACK) Slog.d(TAG_STACK, "clearResumedActivity: " + mResumedActivity + " reason:"
-                + reason);
+    private void setResumedActivity(ActivityRecord r, String reason) {
+        if (mResumedActivity == r) {
+            return;
+        }
 
-        mResumedActivity = null;
+        if (DEBUG_STACK) Slog.d(TAG_STACK, "setResumedActivity stack:" + this + " + from: "
+                + mResumedActivity + " to:" + r + " reason:" + reason);
+        mResumedActivity = r;
     }
 
     @GuardedBy("mService")
@@ -4027,14 +4027,20 @@
      * an activity moves away from the stack.
      */
     void onActivityRemovedFromStack(ActivityRecord r) {
-        if (mResumedActivity == r) {
-            clearResumedActivity("onActivityRemovedFromStack");
+        removeTimeoutsForActivityLocked(r);
+
+        if (mResumedActivity != null && mResumedActivity == r) {
+            setResumedActivity(null, "onActivityRemovedFromStack");
         }
-        if (mPausingActivity == r) {
+        if (mPausingActivity != null && mPausingActivity == r) {
             mPausingActivity = null;
         }
+    }
 
-        removeTimeoutsForActivityLocked(r);
+    void onActivityAddedToStack(ActivityRecord r) {
+        if(r.getState() == RESUMED) {
+            setResumedActivity(r, "onActivityAddedToStack");
+        }
     }
 
     /**
diff --git a/services/core/java/com/android/server/am/TaskRecord.java b/services/core/java/com/android/server/am/TaskRecord.java
index 034cb2e..fccd685 100644
--- a/services/core/java/com/android/server/am/TaskRecord.java
+++ b/services/core/java/com/android/server/am/TaskRecord.java
@@ -927,7 +927,26 @@
         if (stack != null && !stack.isInStackLocked(this)) {
             throw new IllegalStateException("Task must be added as a Stack child first.");
         }
+        final ActivityStack oldStack = mStack;
         mStack = stack;
+
+        // If the new {@link TaskRecord} is from a different {@link ActivityStack}, remove this
+        // {@link ActivityRecord} from its current {@link ActivityStack}.
+
+        if (oldStack != mStack) {
+            for (int i = getChildCount() - 1; i >= 0; --i) {
+                final ActivityRecord activity = getChildAt(i);
+
+                if (oldStack != null) {
+                    oldStack.onActivityRemovedFromStack(activity);
+                }
+
+                if (mStack != null) {
+                    stack.onActivityAddedToStack(activity);
+                }
+            }
+        }
+
         onParentChanged();
     }
 
@@ -1232,6 +1251,7 @@
 
         index = Math.min(size, index);
         mActivities.add(index, r);
+
         updateEffectiveIntent();
         if (r.isPersistable()) {
             mService.notifyTaskPersisterLocked(this, false);
@@ -1257,7 +1277,7 @@
      * @return true if this was the last activity in the task.
      */
     boolean removeActivity(ActivityRecord r) {
-        return removeActivity(r, false /*reparenting*/);
+        return removeActivity(r, false /* reparenting */);
     }
 
     boolean removeActivity(ActivityRecord r, boolean reparenting) {
@@ -1266,7 +1286,7 @@
                     "Activity=" + r + " does not belong to task=" + this);
         }
 
-        r.setTask(null /*task*/, reparenting);
+        r.setTask(null /* task */, reparenting /* reparenting */);
 
         if (mActivities.remove(r) && r.fullscreen) {
             // Was previously in list.
diff --git a/services/tests/servicestests/src/com/android/server/am/ActivityStackTests.java b/services/tests/servicestests/src/com/android/server/am/ActivityStackTests.java
index c78fcd3..4b8dcc1 100644
--- a/services/tests/servicestests/src/com/android/server/am/ActivityStackTests.java
+++ b/services/tests/servicestests/src/com/android/server/am/ActivityStackTests.java
@@ -103,7 +103,42 @@
         assertEquals(mStack.getResumedActivity(), r);
         r.setState(PAUSING, "testResumedActivity");
         assertEquals(mStack.getResumedActivity(), null);
+    }
 
+    @Test
+    public void testResumedActivityFromTaskReparenting() {
+        final ActivityRecord r = new ActivityBuilder(mService).setTask(mTask).build();
+        // Ensure moving task between two stacks updates resumed activity
+        r.setState(RESUMED, "testResumedActivityFromTaskReparenting");
+        assertEquals(mStack.getResumedActivity(), r);
+
+        final ActivityStack destStack = mService.mStackSupervisor.getDefaultDisplay().createStack(
+                WINDOWING_MODE_FULLSCREEN, ACTIVITY_TYPE_STANDARD, true /* onTop */);
+
+        mTask.reparent(destStack, true /* toTop */, TaskRecord.REPARENT_KEEP_STACK_AT_FRONT,
+                false /* animate */, true /* deferResume*/,
+                "testResumedActivityFromTaskReparenting");
+
+        assertEquals(mStack.getResumedActivity(), null);
+        assertEquals(destStack.getResumedActivity(), r);
+    }
+
+    @Test
+    public void testResumedActivityFromActivityReparenting() {
+        final ActivityRecord r = new ActivityBuilder(mService).setTask(mTask).build();
+        // Ensure moving task between two stacks updates resumed activity
+        r.setState(RESUMED, "testResumedActivityFromActivityReparenting");
+        assertEquals(mStack.getResumedActivity(), r);
+
+        final ActivityStack destStack = mService.mStackSupervisor.getDefaultDisplay().createStack(
+                WINDOWING_MODE_FULLSCREEN, ACTIVITY_TYPE_STANDARD, true /* onTop */);
+        final TaskRecord destTask = new TaskBuilder(mSupervisor).setStack(destStack).build();
+
+        mTask.removeActivity(r);
+        destTask.addActivityToTop(r);
+
+        assertEquals(mStack.getResumedActivity(), null);
+        assertEquals(destStack.getResumedActivity(), r);
     }
 
     @Test
@@ -543,5 +578,4 @@
 
         assertEquals(expected, mStack.shouldSleepActivities());
     }
-
 }