Get TaskRecord children with getChildAt & co. APIs (54/n)

Helps reduce work with Task level unification.
Bug: 80414790
Test: Existing tests pass

Change-Id: I5e019c7d1f3ed50c4efd628b68fee6990841904d

11 files changed, 157 insertions, 165 deletions

diff --git a/services/core/java/com/android/server/wm/ActivityDisplay.java b/services/core/java/com/android/server/wm/ActivityDisplay.java
index 9d9a37c13bdd..673366f34fc2 100644
--- a/services/core/java/com/android/server/wm/ActivityDisplay.java
+++ b/services/core/java/com/android/server/wm/ActivityDisplay.java
@@ -1430,9 +1430,8 @@ class ActivityDisplay extends ConfigurationContainer<ActivityStack> {
                 continue;
             }
 
-            final ArrayList<ActivityRecord> activities = task.mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord r = activities.get(activityNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 if (r.isActivityTypeHome()
                         && ((userId == UserHandle.USER_ALL) || (r.mUserId == userId))) {
                     return r;
diff --git a/services/core/java/com/android/server/wm/ActivityMetricsLogger.java b/services/core/java/com/android/server/wm/ActivityMetricsLogger.java
index a0a296792680..ef8c02004116 100644
--- a/services/core/java/com/android/server/wm/ActivityMetricsLogger.java
+++ b/services/core/java/com/android/server/wm/ActivityMetricsLogger.java
@@ -527,8 +527,8 @@ class ActivityMetricsLogger {
     }
 
     private boolean hasVisibleNonFinishingActivity(TaskRecord t) {
-        for (int i = t.mActivities.size() - 1; i >= 0; --i) {
-            final ActivityRecord r = t.mActivities.get(i);
+        for (int i = t.getChildCount() - 1; i >= 0; --i) {
+            final ActivityRecord r = t.getChildAt(i);
             if (r.visible && !r.finishing) {
                 return true;
             }
diff --git a/services/core/java/com/android/server/wm/ActivityRecord.java b/services/core/java/com/android/server/wm/ActivityRecord.java
index 4f52d9df817a..74762494e61d 100644
--- a/services/core/java/com/android/server/wm/ActivityRecord.java
+++ b/services/core/java/com/android/server/wm/ActivityRecord.java
@@ -1577,12 +1577,12 @@ final class ActivityRecord extends AppWindowToken {
                     task.mTaskId, shortComponentName, reason);
             final ArrayList<ActivityRecord> activities = task.mActivities;
             final int index = activities.indexOf(this);
-            if (index < (activities.size() - 1)) {
+            if (index < (task.getChildCount() - 1)) {
                 if ((intent.getFlags() & Intent.FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET) != 0) {
                     // If the caller asked that this activity (and all above it)
                     // be cleared when the task is reset, don't lose that information,
                     // but propagate it up to the next activity.
-                    final ActivityRecord next = activities.get(index + 1);
+                    final ActivityRecord next = task.getChildAt(index + 1);
                     next.intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET);
                 }
             }
@@ -2788,12 +2788,12 @@ final class ActivityRecord extends AppWindowToken {
         if (positionInTask == -1) {
             throw new IllegalStateException("Activity not found in its task");
         }
-        if (positionInTask == task.mActivities.size() - 1) {
+        if (positionInTask == task.getChildCount() - 1) {
             // It's the topmost activity in the task - should become resumed now
             return true;
         }
         // Check if activity above is finishing now and this one becomes the topmost in task.
-        final ActivityRecord activityAbove = task.mActivities.get(positionInTask + 1);
+        final ActivityRecord activityAbove = task.getChildAt(positionInTask + 1);
         if (activityAbove.finishing && results == null) {
             // We will only allow making active if activity above wasn't launched for result.
             // Otherwise it will cause this activity to resume before getting result.
@@ -2848,7 +2848,7 @@ final class ActivityRecord extends AppWindowToken {
         stopped = false;
 
         if (isActivityTypeHome()) {
-            mStackSupervisor.updateHomeProcess(task.mActivities.get(0).app);
+            mStackSupervisor.updateHomeProcess(task.getChildAt(0).app);
         }
 
         if (nowVisible) {
diff --git a/services/core/java/com/android/server/wm/ActivityStack.java b/services/core/java/com/android/server/wm/ActivityStack.java
index 595925442053..11c1e36ce5ce 100644
--- a/services/core/java/com/android/server/wm/ActivityStack.java
+++ b/services/core/java/com/android/server/wm/ActivityStack.java
@@ -488,7 +488,7 @@ class ActivityStack extends ConfigurationContainer {
     int numActivities() {
         int count = 0;
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
-            count += mTaskHistory.get(taskNdx).mActivities.size();
+            count += mTaskHistory.get(taskNdx).getChildCount();
         }
         return count;
     }
@@ -1077,9 +1077,8 @@ class ActivityStack extends ConfigurationContainer {
     ActivityRecord topRunningNonOverlayTaskActivity() {
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
             final TaskRecord task = mTaskHistory.get(taskNdx);
-            final ArrayList<ActivityRecord> activities = task.mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord r = activities.get(activityNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 if (!r.finishing && !r.mTaskOverlay) {
                     return r;
                 }
@@ -1091,9 +1090,8 @@ class ActivityStack extends ConfigurationContainer {
     ActivityRecord topRunningNonDelayedActivityLocked(ActivityRecord notTop) {
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
             final TaskRecord task = mTaskHistory.get(taskNdx);
-            final ArrayList<ActivityRecord> activities = task.mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                ActivityRecord r = activities.get(activityNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 if (!r.finishing && !r.delayedResume && r != notTop && r.okToShowLocked()) {
                     return r;
                 }
@@ -1117,9 +1115,8 @@ class ActivityStack extends ConfigurationContainer {
             if (task.mTaskId == taskId) {
                 continue;
             }
-            ArrayList<ActivityRecord> activities = task.mActivities;
-            for (int i = activities.size() - 1; i >= 0; --i) {
-                final ActivityRecord r = activities.get(i);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 // Note: the taskId check depends on real taskId fields being non-zero
                 if (!r.finishing && (token != r.appToken) && r.okToShowLocked()) {
                     return r;
@@ -1431,10 +1428,8 @@ class ActivityStack extends ConfigurationContainer {
 
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
             final TaskRecord task = mTaskHistory.get(taskNdx);
-            final ArrayList<ActivityRecord> activities = task.mActivities;
-
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                ActivityRecord r = activities.get(activityNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 if (!r.okToShowLocked()) {
                     continue;
                 }
@@ -1500,9 +1495,10 @@ class ActivityStack extends ConfigurationContainer {
     void awakeFromSleepingLocked() {
         // Ensure activities are no longer sleeping.
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
-            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                activities.get(activityNdx).setSleeping(false);
+            final TaskRecord task = mTaskHistory.get(taskNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
+                r.setSleeping(false);
             }
         }
         if (mPausingActivity != null) {
@@ -1516,9 +1512,9 @@ class ActivityStack extends ConfigurationContainer {
         final int userId = UserHandle.getUserId(aInfo.uid);
 
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
-            final List<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord ar = activities.get(activityNdx);
+            final TaskRecord task = mTaskHistory.get(taskNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord ar = task.getChildAt(activityNdx);
 
                 if ((userId == ar.mUserId) && packageName.equals(ar.packageName)) {
                     ar.updateApplicationInfo(aInfo);
@@ -1594,9 +1590,9 @@ class ActivityStack extends ConfigurationContainer {
         // Make sure any paused or stopped but visible activities are now sleeping.
         // This ensures that the activity's onStop() is called.
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
-            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord r = activities.get(activityNdx);
+            final TaskRecord task = mTaskHistory.get(taskNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 if (r.isState(STARTED, STOPPING, STOPPED, PAUSED, PAUSING)) {
                     r.setSleeping(true);
                 }
@@ -1880,9 +1876,8 @@ class ActivityStack extends ConfigurationContainer {
         }
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
             final TaskRecord task = mTaskHistory.get(taskNdx);
-            final ArrayList<ActivityRecord> activities = task.mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord r = activities.get(activityNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
 
                 if (r.finishing) {
                     // We don't factor in finishing activities when determining translucency since
@@ -2113,9 +2108,8 @@ class ActivityStack extends ConfigurationContainer {
                     && top != null && !top.mLaunchTaskBehind;
             for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
                 final TaskRecord task = mTaskHistory.get(taskNdx);
-                final ArrayList<ActivityRecord> activities = task.mActivities;
-                for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                    final ActivityRecord r = activities.get(activityNdx);
+                for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                    final ActivityRecord r = task.getChildAt(activityNdx);
                     final boolean isTop = r == top;
                     if (aboveTop && !isTop) {
                         continue;
@@ -2363,9 +2357,8 @@ class ActivityStack extends ConfigurationContainer {
     void clearOtherAppTimeTrackers(AppTimeTracker except) {
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
             final TaskRecord task = mTaskHistory.get(taskNdx);
-            final ArrayList<ActivityRecord> activities = task.mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord r = activities.get(activityNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 if ( r.appTimeTracker != except) {
                     r.appTimeTracker = null;
                 }
@@ -2423,9 +2416,9 @@ class ActivityStack extends ConfigurationContainer {
         }
 
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
-            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord r = activities.get(activityNdx);
+            final TaskRecord task = mTaskHistory.get(taskNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 if (aboveTop) {
                     if (r == topActivity) {
                         aboveTop = false;
@@ -3210,14 +3203,13 @@ class ActivityStack extends ConfigurationContainer {
 
         // We only do this for activities that are not the root of the task (since if we finish
         // the root, we may no longer have the task!).
-        final ArrayList<ActivityRecord> activities = task.mActivities;
-        final int numActivities = activities.size();
+        final int numActivities = task.getChildCount();
         int lastActivityNdx = task.findRootIndex(true /* effectiveRoot */);
         if (lastActivityNdx == -1) {
             lastActivityNdx = 0;
         }
         for (int i = numActivities - 1; i > lastActivityNdx; --i) {
-            ActivityRecord target = activities.get(i);
+            ActivityRecord target = task.getChildAt(i);
             // TODO: Why is this needed? Looks like we're breaking the loop before we reach the root
             if (target.isRootOfTask()) break;
 
@@ -3257,7 +3249,7 @@ class ActivityStack extends ConfigurationContainer {
                 final TaskRecord targetTask;
                 final ActivityRecord bottom =
                         !mTaskHistory.isEmpty() && !mTaskHistory.get(0).mActivities.isEmpty() ?
-                                mTaskHistory.get(0).mActivities.get(0) : null;
+                                mTaskHistory.get(0).getChildAt(0) : null;
                 if (bottom != null && target.taskAffinity.equals(bottom.getTaskRecord().affinity)) {
                     // If the activity currently at the bottom has the
                     // same task affinity as the one we are moving,
@@ -3279,7 +3271,7 @@ class ActivityStack extends ConfigurationContainer {
                 boolean noOptions = canMoveOptions;
                 final int start = replyChainEnd < 0 ? i : replyChainEnd;
                 for (int srcPos = start; srcPos >= i; --srcPos) {
-                    final ActivityRecord p = activities.get(srcPos);
+                    final ActivityRecord p = task.getChildAt(srcPos);
                     if (p.finishing) {
                         continue;
                     }
@@ -3312,7 +3304,7 @@ class ActivityStack extends ConfigurationContainer {
                     // In this case, we want to finish this activity
                     // and everything above it, so be sneaky and pretend
                     // like these are all in the reply chain.
-                    end = activities.size() - 1;
+                    end = task.getChildCount() - 1;
                 } else if (replyChainEnd < 0) {
                     end = i;
                 } else {
@@ -3320,7 +3312,7 @@ class ActivityStack extends ConfigurationContainer {
                 }
                 boolean noOptions = canMoveOptions;
                 for (int srcPos = i; srcPos <= end; srcPos++) {
-                    ActivityRecord p = activities.get(srcPos);
+                    ActivityRecord p = task.getChildAt(srcPos);
                     if (p.finishing) {
                         continue;
                     }
@@ -3389,8 +3381,7 @@ class ActivityStack extends ConfigurationContainer {
         int replyChainEnd = -1;
         final String taskAffinity = task.affinity;
 
-        final ArrayList<ActivityRecord> activities = affinityTask.mActivities;
-        final int numActivities = activities.size();
+        final int numActivities = task.getChildCount();
 
         // Do not operate on or below the effective root Activity.
         int lastActivityNdx = affinityTask.findRootIndex(true /* effectiveRoot */);
@@ -3398,7 +3389,7 @@ class ActivityStack extends ConfigurationContainer {
             lastActivityNdx = 0;
         }
         for (int i = numActivities - 1; i > lastActivityNdx; --i) {
-            ActivityRecord target = activities.get(i);
+            ActivityRecord target = task.getChildAt(i);
             // TODO: Why is this needed? Looks like we're breaking the loop before we reach the root
             if (target.isRootOfTask()) break;
 
@@ -3435,7 +3426,7 @@ class ActivityStack extends ConfigurationContainer {
                     if (DEBUG_TASKS) Slog.v(TAG_TASKS,
                             "Finishing task at index " + start + " to " + i);
                     for (int srcPos = start; srcPos >= i; --srcPos) {
-                        final ActivityRecord p = activities.get(srcPos);
+                        final ActivityRecord p = task.getChildAt(srcPos);
                         if (p.finishing) {
                             continue;
                         }
@@ -3443,7 +3434,7 @@ class ActivityStack extends ConfigurationContainer {
                     }
                 } else {
                     if (taskInsertionPoint < 0) {
-                        taskInsertionPoint = task.mActivities.size();
+                        taskInsertionPoint = task.getChildCount();
 
                     }
 
@@ -3452,7 +3443,7 @@ class ActivityStack extends ConfigurationContainer {
                             "Reparenting from task=" + affinityTask + ":" + start + "-" + i
                             + " to task=" + task + ":" + taskInsertionPoint);
                     for (int srcPos = start; srcPos >= i; --srcPos) {
-                        final ActivityRecord p = activities.get(srcPos);
+                        final ActivityRecord p = task.getChildAt(srcPos);
                         p.reparent(task, taskInsertionPoint, "resetAffinityTaskIfNeededLocked");
 
                         if (DEBUG_ADD_REMOVE) Slog.i(TAG_ADD_REMOVE,
@@ -3589,9 +3580,9 @@ class ActivityStack extends ConfigurationContainer {
     /** Finish all activities that were started for result from the specified activity. */
     final void finishSubActivityLocked(ActivityRecord self, String resultWho, int requestCode) {
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
-            ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                ActivityRecord r = activities.get(activityNdx);
+            final TaskRecord task = mTaskHistory.get(taskNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 if (r.resultTo == self && r.requestCode == requestCode) {
                     if ((r.resultWho == null && resultWho == null) ||
                         (r.resultWho != null && r.resultWho.equals(resultWho))) {
@@ -3637,11 +3628,11 @@ class ActivityStack extends ConfigurationContainer {
                 if (taskNdx < 0) {
                     break;
                 }
-                activityNdx = mTaskHistory.get(taskNdx).mActivities.size() - 1;
+                activityNdx = mTaskHistory.get(taskNdx).getChildCount() - 1;
             } while (activityNdx < 0);
         }
         if (activityNdx >= 0) {
-            r = mTaskHistory.get(taskNdx).mActivities.get(activityNdx);
+            r = mTaskHistory.get(taskNdx).getChildAt(activityNdx);
             if (r.isState(STARTED, RESUMED, PAUSING, PAUSED)) {
                 if (!r.isActivityTypeHome() || mService.mHomeProcess != r.app) {
                     Slog.w(TAG, "  Force finishing activity "
@@ -3659,8 +3650,8 @@ class ActivityStack extends ConfigurationContainer {
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
             TaskRecord tr = mTaskHistory.get(taskNdx);
             if (tr.voiceSession != null && tr.voiceSession.asBinder() == sessionBinder) {
-                for (int activityNdx = tr.mActivities.size() - 1; activityNdx >= 0; --activityNdx) {
-                    ActivityRecord r = tr.mActivities.get(activityNdx);
+                for (int activityNdx = tr.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                    ActivityRecord r = tr.getChildAt(activityNdx);
                     if (!r.finishing) {
                         r.finishIfPossible("finish-voice", false /* oomAdj */);
                         didOne = true;
@@ -3668,8 +3659,8 @@ class ActivityStack extends ConfigurationContainer {
                 }
             } else {
                 // Check if any of the activities are using voice
-                for (int activityNdx = tr.mActivities.size() - 1; activityNdx >= 0; --activityNdx) {
-                    ActivityRecord r = tr.mActivities.get(activityNdx);
+                for (int activityNdx = tr.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                    ActivityRecord r = tr.getChildAt(activityNdx);
                     if (r.voiceSession != null && r.voiceSession.asBinder() == sessionBinder) {
                         // Inform of cancellation
                         r.clearVoiceSessionLocked();
@@ -3695,9 +3686,9 @@ class ActivityStack extends ConfigurationContainer {
     void finishAllActivitiesImmediately() {
         boolean noActivitiesInStack = true;
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
-            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord r = activities.get(activityNdx);
+            final TaskRecord task = mTaskHistory.get(taskNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 noActivitiesInStack = false;
                 Slog.d(TAG, "finishAllActivitiesImmediatelyLocked: finishing " + r);
                 r.destroyIfPossible("finishAllActivitiesImmediatelyLocked");
@@ -3765,12 +3756,12 @@ class ActivityStack extends ConfigurationContainer {
             return false;
         }
         int finishTo = start - 1;
-        ActivityRecord parent = finishTo < 0 ? null : activities.get(finishTo);
+        ActivityRecord parent = finishTo < 0 ? null : task.getChildAt(finishTo);
         boolean foundParentInTask = false;
         final ComponentName dest = destIntent.getComponent();
         if (start > 0 && dest != null) {
             for (int i = finishTo; i >= 0; i--) {
-                ActivityRecord r = activities.get(i);
+                ActivityRecord r = task.getChildAt(i);
                 if (r.info.packageName.equals(dest.getPackageName()) &&
                         r.info.name.equals(dest.getClassName())) {
                     finishTo = i;
@@ -3931,9 +3922,9 @@ class ActivityStack extends ConfigurationContainer {
         boolean lastIsOpaque = false;
         boolean activityRemoved = false;
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
-            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord r = activities.get(activityNdx);
+            final TaskRecord task = mTaskHistory.get(taskNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 if (r.finishing) {
                     continue;
                 }
@@ -3978,15 +3969,14 @@ class ActivityStack extends ConfigurationContainer {
             }
             if (DEBUG_RELEASE) Slog.d(TAG_RELEASE, "Looking for activities to release in " + task);
             int curNum = 0;
-            final ArrayList<ActivityRecord> activities = task.mActivities;
-            for (int actNdx = 0; actNdx < activities.size(); actNdx++) {
-                final ActivityRecord activity = activities.get(actNdx);
+            for (int actNdx = 0; actNdx < task.getChildCount(); actNdx++) {
+                final ActivityRecord activity = task.getChildAt(actNdx);
                 if (activity.app == app && activity.isDestroyable()) {
                     if (DEBUG_RELEASE) Slog.v(TAG_RELEASE, "Destroying " + activity
                             + " in state " + activity.getState() + " resumed=" + mResumedActivity
                             + " pausing=" + mPausingActivity + " for reason " + reason);
                     activity.destroyImmediately(true /* removeFromApp */, reason);
-                    if (activities.get(actNdx) != activity) {
+                    if (task.getChildAt(actNdx) != activity) {
                         // Was removed from list, back up so we don't miss the next one.
                         actNdx--;
                     }
@@ -4170,8 +4160,8 @@ class ActivityStack extends ConfigurationContainer {
 
         if (timeTracker != null) {
             // The caller wants a time tracker associated with this task.
-            for (int i = tr.mActivities.size() - 1; i >= 0; i--) {
-                tr.mActivities.get(i).appTimeTracker = timeTracker;
+            for (int i = tr.getChildCount() - 1; i >= 0; i--) {
+                tr.getChildAt(i).appTimeTracker = timeTracker;
             }
         }
 
@@ -4425,9 +4415,9 @@ class ActivityStack extends ConfigurationContainer {
 
     boolean willActivityBeVisibleLocked(IBinder token) {
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
-            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord r = activities.get(activityNdx);
+            final TaskRecord task = mTaskHistory.get(taskNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 if (r.appToken == token) {
                     return true;
                 }
@@ -4447,9 +4437,9 @@ class ActivityStack extends ConfigurationContainer {
 
     void closeSystemDialogsLocked() {
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
-            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord r = activities.get(activityNdx);
+            final TaskRecord task = mTaskHistory.get(taskNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 if ((r.info.flags&ActivityInfo.FLAG_FINISH_ON_CLOSE_SYSTEM_DIALOGS) != 0) {
                     r.finishIfPossible("close-sys", true /* oomAdj */);
                 }
@@ -4556,10 +4546,10 @@ class ActivityStack extends ConfigurationContainer {
         final int top = mTaskHistory.size() - 1;
         if (DEBUG_SWITCH) Slog.d(TAG_SWITCH, "Performing unhandledBack(): top activity at " + top);
         if (top >= 0) {
-            final ArrayList<ActivityRecord> activities = mTaskHistory.get(top).mActivities;
-            int activityTop = activities.size() - 1;
+            final TaskRecord task = mTaskHistory.get(top);
+            int activityTop = task.getChildCount() - 1;
             if (activityTop >= 0) {
-                activities.get(activityTop).finishIfPossible("unhandled-back", true /* oomAdj */);
+                task.getChildAt(activityTop).finishIfPossible("unhandled-back", true /* oomAdj */);
             }
         }
     }
@@ -4585,9 +4575,9 @@ class ActivityStack extends ConfigurationContainer {
 
     void handleAppCrash(WindowProcessController app) {
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
-            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord r = activities.get(activityNdx);
+            final TaskRecord task = mTaskHistory.get(taskNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = task.getChildAt(activityNdx);
                 if (r.app == app) {
                     Slog.w(TAG, "  Force finishing activity "
                             + r.intent.getComponent().flattenToShortString());
@@ -4705,9 +4695,9 @@ class ActivityStack extends ConfigurationContainer {
         // All activities that came from the package must be
         // restarted as if there was a config change.
         for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
-            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
-            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord a = activities.get(activityNdx);
+            final TaskRecord task = mTaskHistory.get(taskNdx);
+            for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord a = task.getChildAt(activityNdx);
                 if (a.info.packageName.equals(packageName)) {
                     a.forceNewConfig = true;
                     if (starting != null && a == starting && a.visible) {
diff --git a/services/core/java/com/android/server/wm/ActivityStackSupervisor.java b/services/core/java/com/android/server/wm/ActivityStackSupervisor.java
index f1284d81bfbf..a262f160fee2 100644
--- a/services/core/java/com/android/server/wm/ActivityStackSupervisor.java
+++ b/services/core/java/com/android/server/wm/ActivityStackSupervisor.java
@@ -824,7 +824,7 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
                         System.identityHashCode(r), task.mTaskId, r.shortComponentName);
                 if (r.isActivityTypeHome()) {
                     // Home process is the root process of the task.
-                    updateHomeProcess(task.mActivities.get(0).app);
+                    updateHomeProcess(task.getChildAt(0).app);
                 }
                 mService.getPackageManagerInternalLocked().notifyPackageUse(
                         r.intent.getComponent().getPackageName(), NOTIFY_PACKAGE_USE_ACTIVITY);
@@ -1899,9 +1899,9 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
         task.createTask(onTop, true /* showForAllUsers */);
         if (DEBUG_RECENTS) Slog.v(TAG_RECENTS,
                 "Added restored task=" + task + " to stack=" + stack);
-        final ArrayList<ActivityRecord> activities = task.mActivities;
-        for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
-            activities.get(activityNdx).setTask(task);
+        for (int activityNdx = task.getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+            final ActivityRecord r = task.getChildAt(activityNdx);
+            r.setTask(task);
         }
         return true;
     }
@@ -2501,8 +2501,8 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
             return;
         }
 
-        for (int i = task.mActivities.size() - 1; i >= 0; i--) {
-            final ActivityRecord r = task.mActivities.get(i);
+        for (int i = task.getChildCount() - 1; i >= 0; i--) {
+            final ActivityRecord r = task.getChildAt(i);
             if (r.attachedToProcess()) {
                 mMultiWindowModeChangedActivities.add(r);
             }
@@ -2524,8 +2524,8 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
     }
 
     void scheduleUpdatePictureInPictureModeIfNeeded(TaskRecord task, Rect targetStackBounds) {
-        for (int i = task.mActivities.size() - 1; i >= 0; i--) {
-            final ActivityRecord r = task.mActivities.get(i);
+        for (int i = task.getChildCount() - 1; i >= 0; i--) {
+            final ActivityRecord r = task.getChildAt(i);
             if (r.attachedToProcess()) {
                 mPipModeChangedActivities.add(r);
                 // If we are scheduling pip change, then remove this activity from multi-window
@@ -2543,8 +2543,8 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
 
     void updatePictureInPictureMode(TaskRecord task, Rect targetStackBounds, boolean forceUpdate) {
         mHandler.removeMessages(REPORT_PIP_MODE_CHANGED_MSG);
-        for (int i = task.mActivities.size() - 1; i >= 0; i--) {
-            final ActivityRecord r = task.mActivities.get(i);
+        for (int i = task.getChildCount() - 1; i >= 0; i--) {
+            final ActivityRecord r = task.getChildAt(i);
             if (r.attachedToProcess()) {
                 r.updatePictureInPictureMode(targetStackBounds, forceUpdate);
             }
diff --git a/services/core/java/com/android/server/wm/ActivityStarter.java b/services/core/java/com/android/server/wm/ActivityStarter.java
index 939789307333..b68ba7cc7961 100644
--- a/services/core/java/com/android/server/wm/ActivityStarter.java
+++ b/services/core/java/com/android/server/wm/ActivityStarter.java
@@ -2430,7 +2430,7 @@ class ActivityStarter {
         if (mStartActivity.getTaskRecord() == null || mStartActivity.getTaskRecord() == parent) {
             parent.addActivityToTop(mStartActivity);
         } else {
-            mStartActivity.reparent(parent, parent.mActivities.size() /* top */, reason);
+            mStartActivity.reparent(parent, parent.getChildCount() /* top */, reason);
         }
     }
 
diff --git a/services/core/java/com/android/server/wm/ActivityTaskManagerService.java b/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
index 750fc6832627..44d748d667a9 100644
--- a/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
+++ b/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
@@ -1982,7 +1982,7 @@ public class ActivityTaskManagerService extends IActivityTaskManager.Stub {
                 final TaskRecord task = r.getTaskRecord();
                 int index = task.mActivities.lastIndexOf(r);
                 if (index > 0) {
-                    ActivityRecord under = task.mActivities.get(index - 1);
+                    ActivityRecord under = task.getChildAt(index - 1);
                     under.returningOptions = safeOptions != null ? safeOptions.getOptions(r) : null;
                 }
                 return r.setOccludesParent(false);
diff --git a/services/core/java/com/android/server/wm/ConfigurationContainer.java b/services/core/java/com/android/server/wm/ConfigurationContainer.java
index 8afbbdf303ab..300ee1ddc77d 100644
--- a/services/core/java/com/android/server/wm/ConfigurationContainer.java
+++ b/services/core/java/com/android/server/wm/ConfigurationContainer.java
@@ -626,6 +626,10 @@ public abstract class ConfigurationContainer<E extends ConfigurationContainer> {
         return mFullConfiguration.windowConfiguration.isAlwaysOnTop();
     }
 
+    boolean hasChild() {
+        return getChildCount() > 0;
+    }
+
     abstract protected int getChildCount();
 
     abstract protected E getChildAt(int index);
diff --git a/services/core/java/com/android/server/wm/RootActivityContainer.java b/services/core/java/com/android/server/wm/RootActivityContainer.java
index d78d517fcfc1..60833c38c9c1 100644
--- a/services/core/java/com/android/server/wm/RootActivityContainer.java
+++ b/services/core/java/com/android/server/wm/RootActivityContainer.java
@@ -983,7 +983,7 @@ class RootActivityContainer extends ConfigurationContainer
             stack.resize(task.getRequestedOverrideBounds(), null /* tempTaskBounds */,
                     null /* tempTaskInsetBounds */, !PRESERVE_WINDOWS, !DEFER_RESUME);
 
-            if (task.mActivities.size() == 1) {
+            if (task.getChildCount() == 1) {
                 // Defer resume until below, and do not schedule PiP changes until we animate below
                 task.reparent(stack, ON_TOP, REPARENT_MOVE_STACK_TO_FRONT, !ANIMATE, DEFER_RESUME,
                         false /* schedulePictureInPictureModeChange */, reason);
diff --git a/services/core/java/com/android/server/wm/TaskRecord.java b/services/core/java/com/android/server/wm/TaskRecord.java
index 75333c728e0b..ab661cad865f 100644
--- a/services/core/java/com/android/server/wm/TaskRecord.java
+++ b/services/core/java/com/android/server/wm/TaskRecord.java
@@ -447,7 +447,7 @@ class TaskRecord extends ConfigurationContainer {
     }
 
     void cleanUpResourcesForDestroy() {
-        if (!mActivities.isEmpty()) {
+        if (hasChild()) {
             return;
         }
 
@@ -1095,7 +1095,7 @@ class TaskRecord extends ConfigurationContainer {
             // There are no non-finishing activities in the task.
             return null;
         }
-        return mActivities.get(rootActivityIndex);
+        return getChildAt(rootActivityIndex);
     }
 
     ActivityRecord getTopActivity() {
@@ -1103,8 +1103,8 @@ class TaskRecord extends ConfigurationContainer {
     }
 
     ActivityRecord getTopActivity(boolean includeOverlays) {
-        for (int i = mActivities.size() - 1; i >= 0; --i) {
-            final ActivityRecord r = mActivities.get(i);
+        for (int i = getChildCount() - 1; i >= 0; --i) {
+            final ActivityRecord r = getChildAt(i);
             if (r.finishing || (!includeOverlays && r.mTaskOverlay)) {
                 continue;
             }
@@ -1115,8 +1115,8 @@ class TaskRecord extends ConfigurationContainer {
 
     ActivityRecord topRunningActivityLocked() {
         if (mStack != null) {
-            for (int activityNdx = mActivities.size() - 1; activityNdx >= 0; --activityNdx) {
-                ActivityRecord r = mActivities.get(activityNdx);
+            for (int activityNdx = getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                ActivityRecord r = getChildAt(activityNdx);
                 if (!r.finishing && r.okToShowLocked()) {
                     return r;
                 }
@@ -1126,8 +1126,8 @@ class TaskRecord extends ConfigurationContainer {
     }
 
     boolean isVisible() {
-        for (int i = mActivities.size() - 1; i >= 0; --i) {
-            final ActivityRecord r = mActivities.get(i);
+        for (int i = getChildCount() - 1; i >= 0; --i) {
+            final ActivityRecord r = getChildAt(i);
             if (r.visible) {
                 return true;
             }
@@ -1139,8 +1139,8 @@ class TaskRecord extends ConfigurationContainer {
      * Return true if any activities in this task belongs to input uid.
      */
     boolean containsAppUid(int uid) {
-        for (int i = mActivities.size() - 1; i >= 0; --i) {
-            final ActivityRecord r = mActivities.get(i);
+        for (int i = getChildCount() - 1; i >= 0; --i) {
+            final ActivityRecord r = getChildAt(i);
             if (r.getUid() == uid) {
                 return true;
             }
@@ -1150,8 +1150,8 @@ class TaskRecord extends ConfigurationContainer {
 
     void getAllRunningVisibleActivitiesLocked(ArrayList<ActivityRecord> outActivities) {
         if (mStack != null) {
-            for (int activityNdx = mActivities.size() - 1; activityNdx >= 0; --activityNdx) {
-                ActivityRecord r = mActivities.get(activityNdx);
+            for (int activityNdx = getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                ActivityRecord r = getChildAt(activityNdx);
                 if (!r.finishing && r.okToShowLocked() && r.visibleIgnoringKeyguard) {
                     outActivities.add(r);
                 }
@@ -1161,8 +1161,8 @@ class TaskRecord extends ConfigurationContainer {
 
     ActivityRecord topRunningActivityWithStartingWindowLocked() {
         if (mStack != null) {
-            for (int activityNdx = mActivities.size() - 1; activityNdx >= 0; --activityNdx) {
-                ActivityRecord r = mActivities.get(activityNdx);
+            for (int activityNdx = getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+                ActivityRecord r = getChildAt(activityNdx);
                 if (r.mStartingWindowState != STARTING_WINDOW_SHOWN
                         || r.finishing || !r.okToShowLocked()) {
                     continue;
@@ -1179,8 +1179,8 @@ class TaskRecord extends ConfigurationContainer {
      */
     void getNumRunningActivities(TaskActivitiesReport reportOut) {
         reportOut.reset();
-        for (int i = mActivities.size() - 1; i >= 0; --i) {
-            final ActivityRecord r = mActivities.get(i);
+        for (int i = getChildCount() - 1; i >= 0; --i) {
+            final ActivityRecord r = getChildAt(i);
             if (r.finishing) {
                 continue;
             }
@@ -1227,17 +1227,17 @@ class TaskRecord extends ConfigurationContainer {
     }
 
     void addActivityToTop(ActivityRecord r) {
-        addActivityAtIndex(mActivities.size(), r);
+        addActivityAtIndex(getChildCount(), r);
     }
 
     @Override
     /*@WindowConfiguration.ActivityType*/
     public int getActivityType() {
         final int applicationType = super.getActivityType();
-        if (applicationType != ACTIVITY_TYPE_UNDEFINED || mActivities.isEmpty()) {
+        if (applicationType != ACTIVITY_TYPE_UNDEFINED || !hasChild()) {
             return applicationType;
         }
-        return mActivities.get(0).getActivityType();
+        return getChildAt(0).getActivityType();
     }
 
     /**
@@ -1259,7 +1259,7 @@ class TaskRecord extends ConfigurationContainer {
             numFullscreen++;
         }
         // Only set this based on the first activity
-        if (mActivities.isEmpty()) {
+        if (!hasChild()) {
             if (r.getActivityType() == ACTIVITY_TYPE_UNDEFINED) {
                 // Normally non-standard activity type for the activity record will be set when the
                 // object is created, however we delay setting the standard application type until
@@ -1279,10 +1279,10 @@ class TaskRecord extends ConfigurationContainer {
             r.setActivityType(getActivityType());
         }
 
-        final int size = mActivities.size();
+        final int size = getChildCount();
 
         if (index == size && size > 0) {
-            final ActivityRecord top = mActivities.get(size - 1);
+            final ActivityRecord top = getChildAt(size - 1);
             if (top.mTaskOverlay) {
                 // Place below the task overlay activity since the overlay activity should always
                 // be on top.
@@ -1341,7 +1341,7 @@ class TaskRecord extends ConfigurationContainer {
             mAtmService.getTaskChangeNotificationController().notifyTaskStackChanged();
         }
 
-        if (mActivities.isEmpty()) {
+        if (!hasChild()) {
             return !mReuseTask;
         }
         updateEffectiveIntent();
@@ -1355,8 +1355,8 @@ class TaskRecord extends ConfigurationContainer {
      */
     boolean onlyHasTaskOverlayActivities(boolean excludeFinishing) {
         int count = 0;
-        for (int i = mActivities.size() - 1; i >= 0; i--) {
-            final ActivityRecord r = mActivities.get(i);
+        for (int i = getChildCount() - 1; i >= 0; i--) {
+            final ActivityRecord r = getChildAt(i);
             if (excludeFinishing && r.finishing) {
                 continue;
             }
@@ -1372,7 +1372,7 @@ class TaskRecord extends ConfigurationContainer {
         // We will automatically remove the task either if it has explicitly asked for
         // this, or it is empty and has never contained an activity that got shown to
         // the user.
-        return autoRemoveRecents || (mActivities.isEmpty() && !hasBeenVisible);
+        return autoRemoveRecents || (!hasChild() && !hasBeenVisible);
     }
 
     /**
@@ -1380,9 +1380,9 @@ class TaskRecord extends ConfigurationContainer {
      * task starting at a specified index.
      */
     final void performClearTaskAtIndexLocked(int activityNdx, String reason) {
-        int numActivities = mActivities.size();
+        int numActivities = getChildCount();
         for ( ; activityNdx < numActivities; ++activityNdx) {
-            final ActivityRecord r = mActivities.get(activityNdx);
+            final ActivityRecord r = getChildAt(activityNdx);
             if (r.finishing) {
                 continue;
             }
@@ -1429,9 +1429,9 @@ class TaskRecord extends ConfigurationContainer {
      * or null if none was found.
      */
     final ActivityRecord performClearTaskLocked(ActivityRecord newR, int launchFlags) {
-        int numActivities = mActivities.size();
+        int numActivities = getChildCount();
         for (int activityNdx = numActivities - 1; activityNdx >= 0; --activityNdx) {
-            ActivityRecord r = mActivities.get(activityNdx);
+            ActivityRecord r = getChildAt(activityNdx);
             if (r.finishing) {
                 continue;
             }
@@ -1440,7 +1440,7 @@ class TaskRecord extends ConfigurationContainer {
                 final ActivityRecord ret = r;
 
                 for (++activityNdx; activityNdx < numActivities; ++activityNdx) {
-                    r = mActivities.get(activityNdx);
+                    r = getChildAt(activityNdx);
                     if (r.finishing) {
                         continue;
                     }
@@ -1591,8 +1591,8 @@ class TaskRecord extends ConfigurationContainer {
      */
     final ActivityRecord findActivityInHistoryLocked(ActivityRecord r) {
         final ComponentName realActivity = r.mActivityComponent;
-        for (int activityNdx = mActivities.size() - 1; activityNdx >= 0; --activityNdx) {
-            ActivityRecord candidate = mActivities.get(activityNdx);
+        for (int activityNdx = getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+            ActivityRecord candidate = getChildAt(activityNdx);
             if (candidate.finishing) {
                 continue;
             }
@@ -1609,12 +1609,12 @@ class TaskRecord extends ConfigurationContainer {
         // Traverse upwards looking for any break between main task activities and
         // utility activities.
         int activityNdx;
-        final int numActivities = mActivities.size();
+        final int numActivities = getChildCount();
         final boolean relinquish = numActivities != 0 &&
-                (mActivities.get(0).info.flags & FLAG_RELINQUISH_TASK_IDENTITY) != 0;
+                (getChildAt(0).info.flags & FLAG_RELINQUISH_TASK_IDENTITY) != 0;
         for (activityNdx = Math.min(numActivities, 1); activityNdx < numActivities;
                 ++activityNdx) {
-            final ActivityRecord r = mActivities.get(activityNdx);
+            final ActivityRecord r = getChildAt(activityNdx);
             if (relinquish && (r.info.flags & FLAG_RELINQUISH_TASK_IDENTITY) == 0) {
                 // This will be the top activity for determining taskDescription. Pre-inc to
                 // overcome initial decrement below.
@@ -1642,7 +1642,7 @@ class TaskRecord extends ConfigurationContainer {
             boolean navigationBarContrastWhenTransparent = false;
             boolean topActivity = true;
             for (--activityNdx; activityNdx >= 0; --activityNdx) {
-                final ActivityRecord r = mActivities.get(activityNdx);
+                final ActivityRecord r = getChildAt(activityNdx);
                 if (r.mTaskOverlay) {
                     continue;
                 }
@@ -1697,9 +1697,9 @@ class TaskRecord extends ConfigurationContainer {
      */
     int findRootIndex(boolean effectiveRoot) {
         int effectiveNdx = -1;
-        final int topActivityNdx = mActivities.size() - 1;
+        final int topActivityNdx = getChildCount() - 1;
         for (int activityNdx = 0; activityNdx <= topActivityNdx; ++activityNdx) {
-            final ActivityRecord r = mActivities.get(activityNdx);
+            final ActivityRecord r = getChildAt(activityNdx);
             if (r.finishing) {
                 continue;
             }
@@ -1720,7 +1720,7 @@ class TaskRecord extends ConfigurationContainer {
             // But we still want to update the intent, so let's use the bottom activity.
             effectiveRootIndex = 0;
         }
-        final ActivityRecord r = mActivities.get(effectiveRootIndex);
+        final ActivityRecord r = getChildAt(effectiveRootIndex);
         setIntent(r);
 
         // Update the task description when the activities change
@@ -2289,8 +2289,8 @@ class TaskRecord extends ConfigurationContainer {
     }
 
     void addStartingWindowsForVisibleActivities(boolean taskSwitch) {
-        for (int activityNdx = mActivities.size() - 1; activityNdx >= 0; --activityNdx) {
-            final ActivityRecord r = mActivities.get(activityNdx);
+        for (int activityNdx = getChildCount() - 1; activityNdx >= 0; --activityNdx) {
+            final ActivityRecord r = getChildAt(activityNdx);
             if (r.visible) {
                 r.showStartingWindow(null /* prev */, false /* newTask */, taskSwitch);
             }
@@ -2462,7 +2462,7 @@ class TaskRecord extends ConfigurationContainer {
             sb.append(" StackId=");
             sb.append(getStackId());
             sb.append(" sz=");
-            sb.append(mActivities.size());
+            sb.append(getChildCount());
             sb.append('}');
             return sb.toString();
         }
@@ -2495,8 +2495,8 @@ class TaskRecord extends ConfigurationContainer {
         final long token = proto.start(fieldId);
         super.writeToProto(proto, CONFIGURATION_CONTAINER, logLevel);
         proto.write(ID, mTaskId);
-        for (int i = mActivities.size() - 1; i >= 0; i--) {
-            ActivityRecord activity = mActivities.get(i);
+        for (int i = getChildCount() - 1; i >= 0; i--) {
+            ActivityRecord activity = getChildAt(i);
             activity.writeToProto(proto, ACTIVITIES);
         }
         proto.write(STACK_ID, mStack.mStackId);
@@ -2607,10 +2607,9 @@ class TaskRecord extends ConfigurationContainer {
             out.endTag(null, TAG_INTENT);
         }
 
-        final ArrayList<ActivityRecord> activities = mActivities;
-        final int numActivities = activities.size();
+        final int numActivities = getChildCount();
         for (int activityNdx = 0; activityNdx < numActivities; ++activityNdx) {
-            final ActivityRecord r = activities.get(activityNdx);
+            final ActivityRecord r = getChildAt(activityNdx);
             if (r.info.persistableMode == ActivityInfo.PERSIST_ROOT_ONLY || !r.isPersistable() ||
                     ((r.intent.getFlags() & FLAG_ACTIVITY_NEW_DOCUMENT
                             | FLAG_ACTIVITY_RETAIN_IN_RECENTS) == FLAG_ACTIVITY_NEW_DOCUMENT) &&
diff --git a/services/tests/wmtests/src/com/android/server/wm/ActivityStackTests.java b/services/tests/wmtests/src/com/android/server/wm/ActivityStackTests.java
index c2a05c243540..2835c1fb59ae 100644
--- a/services/tests/wmtests/src/com/android/server/wm/ActivityStackTests.java
+++ b/services/tests/wmtests/src/com/android/server/wm/ActivityStackTests.java
@@ -891,7 +891,7 @@ public class ActivityStackTests extends ActivityTestsBase {
         activity.app = null;
         overlayActivity.app = null;
 
-        assertEquals(2, mTask.mActivities.size());
+        assertEquals(2, mTask.getChildCount());
 
         mStack.finishDisabledPackageActivitiesLocked(activity.packageName,
                 null  /* filterByClasses */, true /* doit */, true /* evenPersistent */,
@@ -900,7 +900,7 @@ public class ActivityStackTests extends ActivityTestsBase {
         // Although the overlay activity is in another package, the non-overlay activities are
         // removed from the task. Since the overlay activity should be removed as well, the task
         // should be empty.
-        assertThat(mTask.mActivities).isEmpty();
+        assertFalse(mTask.hasChild());
         assertThat(mStack.getAllTasks()).isEmpty();
     }
 
@@ -918,11 +918,11 @@ public class ActivityStackTests extends ActivityTestsBase {
         // second activity will be immediately removed as it has no state.
         secondActivity.setSavedState(null /* savedState */);
 
-        assertEquals(2, mTask.mActivities.size());
+        assertEquals(2, mTask.getChildCount());
 
         mStack.handleAppDiedLocked(secondActivity.app);
 
-        assertThat(mTask.mActivities).isEmpty();
+        assertFalse(mTask.hasChild());
         assertThat(mStack.getAllTasks()).isEmpty();
     }
 
@@ -936,7 +936,7 @@ public class ActivityStackTests extends ActivityTestsBase {
 
         mStack.handleAppDiedLocked(activity.app);
 
-        assertEquals(1, mTask.mActivities.size());
+        assertEquals(1, mTask.getChildCount());
         assertEquals(1, mStack.getAllTasks().size());
     }
 
@@ -950,7 +950,7 @@ public class ActivityStackTests extends ActivityTestsBase {
 
         mStack.handleAppDiedLocked(activity.app);
 
-        assertThat(mTask.mActivities).isEmpty();
+        assertFalse(mTask.hasChild());
         assertThat(mStack.getAllTasks()).isEmpty();
     }
 
@@ -964,7 +964,7 @@ public class ActivityStackTests extends ActivityTestsBase {
 
         mStack.handleAppDiedLocked(activity.app);
 
-        assertEquals(1, mTask.mActivities.size());
+        assertEquals(1, mTask.getChildCount());
         assertEquals(1, mStack.getAllTasks().size());
     }
 
@@ -978,7 +978,7 @@ public class ActivityStackTests extends ActivityTestsBase {
 
         mStack.handleAppDiedLocked(activity.app);
 
-        assertThat(mTask.mActivities).isEmpty();
+        assertFalse(mTask.hasChild());
         assertThat(mStack.getAllTasks()).isEmpty();
     }