Merge "5/n Add support for multiple task display areas" into rvc-dev am:... (1b670f16) · Commits · e / os / android_frameworks_base

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

+11 −1

Original line number	Diff line number	Diff line
		@@ -7411,7 +7411,17 @@ final class ActivityRecord extends WindowToken implements WindowManagerService.A
		*/
		boolean isResumedActivityOnDisplay() {
		final DisplayContent display = getDisplay();
		return display != null && this == display.mTaskContainers.getResumedActivity();
		if (display == null) {
		return false;
		}
		for (int tdaNdx = display.getTaskDisplayAreaCount() - 1; tdaNdx >= 0; --tdaNdx) {
		final TaskDisplayArea taskDisplayArea = display.getTaskDisplayAreaAt(tdaNdx);
		final ActivityRecord resumedActivity = taskDisplayArea.getFocusedActivity();
		if (resumedActivity != null) {
		return resumedActivity == this;
		}
		}
		return false;
		}

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

+2 −2

Original line number	Diff line number	Diff line
		@@ -1119,8 +1119,8 @@ class ActivityStack extends Task {

		@Override
		public boolean isAttached() {
		final DisplayContent display = getDisplay();
		return display != null && !display.isRemoved();
		final TaskDisplayArea taskDisplayArea = getDisplayArea();
		return taskDisplayArea != null && !taskDisplayArea.isRemoved();
		}

		// TODO: Should each user have there own stacks?

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

+24 −23

Original line number	Diff line number	Diff line
		@@ -385,15 +385,15 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
		private final MoveTaskToFullscreenHelper mMoveTaskToFullscreenHelper =
		new MoveTaskToFullscreenHelper();
		private class MoveTaskToFullscreenHelper {
		private DisplayContent mToDisplay;
		private TaskDisplayArea mToDisplayArea;
		private boolean mOnTop;
		private Task mTopTask;
		private boolean mSchedulePictureInPictureModeChange;

		void process(ActivityStack fromStack, DisplayContent toDisplay, boolean onTop,
		void process(ActivityStack fromStack, TaskDisplayArea toDisplayArea, boolean onTop,
		boolean schedulePictureInPictureModeChange) {
		mSchedulePictureInPictureModeChange = schedulePictureInPictureModeChange;
		mToDisplay = toDisplay;
		mToDisplayArea = toDisplayArea;
		mOnTop = onTop;
		mTopTask = fromStack.getTopMostTask();

		@@ -401,7 +401,7 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
		MoveTaskToFullscreenHelper::processLeafTask, this, PooledLambda.__(Task.class));
		fromStack.forAllLeafTasks(c, false /* traverseTopToBottom */);
		c.recycle();
		mToDisplay = null;
		mToDisplayArea = null;
		mTopTask = null;
		}

		@@ -411,19 +411,18 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
		task.getActivityType())) {
		final ActivityStack stack = (ActivityStack) task;
		stack.setWindowingMode(WINDOWING_MODE_FULLSCREEN);
		if (mToDisplay.getDisplayId() != stack.getDisplayId()) {
		stack.reparent(mToDisplay.getDefaultTaskDisplayArea(), mOnTop);
		if (mToDisplayArea.getDisplayId() != stack.getDisplayId()) {
		stack.reparent(mToDisplayArea, mOnTop);
		} else if (mOnTop) {
		mToDisplay.mTaskContainers.positionStackAtTop(stack,
		false /* includingParents */);
		mToDisplayArea.positionStackAtTop(stack, false /* includingParents */);
		} else {
		mToDisplay.mTaskContainers.positionStackAtBottom(stack);
		mToDisplayArea.positionStackAtBottom(stack);
		}
		return;
		}

		final ActivityStack toStack = mToDisplay.mTaskContainers.getOrCreateStack(
		null, mTmpOptions, task, task.getActivityType(), mOnTop);
		final ActivityStack toStack = mToDisplayArea.getOrCreateStack(null, mTmpOptions, task,
		task.getActivityType(), mOnTop);
		if (task == toStack) {
		// The task was reused as the root task.
		return;
		@@ -1418,7 +1417,7 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
		mRootWindowContainer.getLaunchStack(null, options, task, ON_TOP);

		if (stack != currentStack) {
		moveHomeStackToFrontIfNeeded(flags, stack.getDisplay(), reason);
		moveHomeStackToFrontIfNeeded(flags, stack.getDisplayArea(), reason);
		task.reparent(stack, ON_TOP, REPARENT_KEEP_STACK_AT_FRONT, !ANIMATE, DEFER_RESUME,
		reason);
		currentStack = stack;
		@@ -1437,7 +1436,7 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
		}

		if (!reparented) {
		moveHomeStackToFrontIfNeeded(flags, currentStack.getDisplay(), reason);
		moveHomeStackToFrontIfNeeded(flags, currentStack.getDisplayArea(), reason);
		}

		final ActivityRecord r = task.getTopNonFinishingActivity();
		@@ -1451,15 +1450,16 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
		currentStack, forceNonResizeable);
		}

		private void moveHomeStackToFrontIfNeeded(int flags, DisplayContent display, String reason) {
		final ActivityStack focusedStack = display.getFocusedStack();
		private void moveHomeStackToFrontIfNeeded(int flags, TaskDisplayArea taskDisplayArea,
		String reason) {
		final ActivityStack focusedStack = taskDisplayArea.getFocusedStack();

		if ((display.getWindowingMode() == WINDOWING_MODE_FULLSCREEN
		if ((taskDisplayArea.getWindowingMode() == WINDOWING_MODE_FULLSCREEN
		&& (flags & ActivityManager.MOVE_TASK_WITH_HOME) != 0)
		\|\| (focusedStack != null && focusedStack.isActivityTypeRecents())) {
		// We move home stack to front when we are on a fullscreen display and caller has
		// We move home stack to front when we are on a fullscreen display area and caller has
		// requested the home activity to move with it. Or the previous stack is recents.
		display.mTaskContainers.moveHomeStackToFront(reason);
		taskDisplayArea.moveHomeStackToFront(reason);
		}
		}

		@@ -1511,15 +1511,15 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
		mService.deferWindowLayout();
		try {
		final int windowingMode = fromStack.getWindowingMode();
		final DisplayContent toDisplay =
		mRootWindowContainer.getDisplayContent(toDisplayId);
		final TaskDisplayArea toDisplayArea = mRootWindowContainer
		.getDisplayContent(toDisplayId).getDefaultTaskDisplayArea();

		if (windowingMode == WINDOWING_MODE_SPLIT_SCREEN_PRIMARY) {
		// We are moving all tasks from the docked stack to the fullscreen stack,
		// which is dismissing the docked stack, so resize all other stacks to
		// fullscreen here already so we don't end up with resize trashing.
		for (int i = toDisplay.getStackCount() - 1; i >= 0; --i) {
		final ActivityStack otherStack = toDisplay.getStackAt(i);
		for (int i = toDisplayArea.getStackCount() - 1; i >= 0; --i) {
		final ActivityStack otherStack = toDisplayArea.getStackAt(i);
		if (!otherStack.inSplitScreenSecondaryWindowingMode()) {
		continue;
		}
		@@ -1535,7 +1535,7 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
		if (fromStack.hasChild()) {
		mTmpOptions.setLaunchWindowingMode(WINDOWING_MODE_FULLSCREEN);
		mMoveTaskToFullscreenHelper.process(
		fromStack, toDisplay, onTop, schedulePictureInPictureModeChange);
		fromStack, toDisplayArea, onTop, schedulePictureInPictureModeChange);
		}

		mRootWindowContainer.ensureActivitiesVisible(null, 0, PRESERVE_WINDOWS);
		@@ -1546,6 +1546,7 @@ public class ActivityStackSupervisor implements RecentTasks.Callbacks {
		}

		void moveTasksToFullscreenStackLocked(ActivityStack fromStack, boolean onTop) {
		// TODO(b/153089193): Support moving within the same task display area
		mWindowManager.inSurfaceTransaction(() ->
		moveTasksToFullscreenStackInSurfaceTransaction(fromStack, DEFAULT_DISPLAY, onTop));
		}

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

+3 −2

Original line number	Diff line number	Diff line
		@@ -189,9 +189,10 @@ public class ActivityStartController {
		mSupervisor.beginDeferResume();
		final ActivityStack homeStack;
		try {
		// TODO(multi-display-area): Support starting home in a task display area
		// Make sure home stack exist on display.
		homeStack = display.mTaskContainers.getOrCreateStack(WINDOWING_MODE_FULLSCREEN,
		ACTIVITY_TYPE_HOME, ON_TOP);
		homeStack = display.getDefaultTaskDisplayArea().getOrCreateStack(
		WINDOWING_MODE_FULLSCREEN, ACTIVITY_TYPE_HOME, ON_TOP);
		} finally {
		mSupervisor.endDeferResume();
		}

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

+119 −80

Original line number	Diff line number	Diff line
		@@ -2060,20 +2060,53 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		* activity type. Null is no compatible stack on the display.
		*/
		ActivityStack getStack(int windowingMode, int activityType) {
		return mTaskContainers.getStack(windowingMode, activityType);
		for (int tdaNdx = getTaskDisplayAreaCount() - 1; tdaNdx >= 0; --tdaNdx) {
		final ActivityStack stack = getTaskDisplayAreaAt(tdaNdx)
		.getStack(windowingMode, activityType);
		if (stack != null) {
		return stack;
		}
		}
		return null;
		}

		protected int getStackCount() {
		return mTaskContainers.mChildren.size();
		protected int getTaskDisplayAreaCount() {
		// TODO(multi-display-area): Report actual display area count
		return 1;
		}

		protected TaskDisplayArea getTaskDisplayAreaAt(int index) {
		// TODO(multi-display-area): Report actual display area values
		return mTaskContainers;
		}

		protected ActivityStack getStackAt(int index) {
		return mTaskContainers.mChildren.get(index);
		ActivityStack getStack(int rootTaskId) {
		for (int tdaNdx = getTaskDisplayAreaCount() - 1; tdaNdx >= 0; --tdaNdx) {
		final ActivityStack stack = getTaskDisplayAreaAt(tdaNdx).getStack(rootTaskId);
		if (stack != null) {
		return stack;
		}
		}
		return null;
		}

		protected int getStackCount() {
		int totalStackCount = 0;
		for (int i = getTaskDisplayAreaCount() - 1; i >= 0; --i) {
		totalStackCount += getTaskDisplayAreaAt(i).getStackCount();
		}
		return totalStackCount;
		}

		@VisibleForTesting
		ActivityStack getTopStack() {
		return mTaskContainers.getTopStack();
		for (int i = getTaskDisplayAreaCount() - 1; i >= 0; --i) {
		final ActivityStack stack = getTaskDisplayAreaAt(i).getTopStack();
		if (stack != null) {
		return stack;
		}
		}
		return null;
		}

		/**
		@@ -2449,7 +2482,7 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		final PooledConsumer c = PooledLambda.obtainConsumer(
		DisplayContent::processTaskForTouchExcludeRegion, this,
		PooledLambda.__(Task.class), focusedTask, delta);
		mTaskContainers.forAllTasks(c);
		forAllTasks(c);
		c.recycle();

		// If we removed the focused task above, add it back and only leave its
		@@ -2630,9 +2663,8 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		}

		void prepareFreezingTaskBounds() {
		for (int stackNdx = mTaskContainers.getChildCount() - 1; stackNdx >= 0; --stackNdx) {
		final ActivityStack stack = mTaskContainers.getChildAt(stackNdx);
		stack.prepareFreezingTaskBounds();
		for (int tdaNdx = getTaskDisplayAreaCount() - 1; tdaNdx >= 0; --tdaNdx) {
		getTaskDisplayAreaAt(tdaNdx).prepareFreezingTaskBounds();
		}
		}

		@@ -2738,8 +2770,8 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		final ActivityStack focusedStack = getFocusedStack();
		if (focusedStack != null) {
		proto.write(FOCUSED_ROOT_TASK_ID, focusedStack.getRootTaskId());
		final ActivityRecord focusedActivity = focusedStack.getDisplay().mTaskContainers
		.getResumedActivity();
		final ActivityRecord focusedActivity = focusedStack.getDisplayArea()
		.getFocusedActivity();
		if (focusedActivity != null) {
		focusedActivity.writeIdentifierToProto(proto, RESUMED_ACTIVITY);
		}
		@@ -2797,13 +2829,6 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		if (mLastFocus != mCurrentFocus) {
		pw.print(" mLastFocus="); pw.println(mLastFocus);
		}
		if (mTaskContainers.mPreferredTopFocusableStack != null) {
		pw.println(prefix + "mPreferredTopFocusableStack="
		+ mTaskContainers.mPreferredTopFocusableStack);
		}
		if (mTaskContainers.mLastFocusedStack != null) {
		pw.println(prefix + "mLastFocusedStack=" + mTaskContainers.mLastFocusedStack);
		}
		if (mLosingFocus.size() > 0) {
		pw.println();
		pw.println(" Windows losing focus:");
		@@ -2837,10 +2862,9 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		}

		pw.println();
		pw.println(prefix + "Application tokens in top down Z order:");
		for (int stackNdx = mTaskContainers.getChildCount() - 1; stackNdx >= 0; --stackNdx) {
		final ActivityStack stack = mTaskContainers.getChildAt(stackNdx);
		stack.dump(pw, prefix + " ", dumpAll);
		pw.println(prefix + "Task display areas in top down Z order:");
		for (int tdaNdx = getTaskDisplayAreaCount() - 1; tdaNdx >= 0; --tdaNdx) {
		getTaskDisplayAreaAt(tdaNdx).dump(pw, prefix + " ", dumpAll);
		}

		pw.println();
		@@ -4002,7 +4026,9 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		}

		// Initialize state of exiting applications.
		mTaskContainers.setExitingTokensHasVisible(hasVisible);
		for (int i = getTaskDisplayAreaCount() - 1; i >= 0; --i) {
		getTaskDisplayAreaAt(i).setExitingTokensHasVisible(hasVisible);
		}
		}

		void removeExistingTokensIfPossible() {
		@@ -4014,7 +4040,9 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		}

		// Time to remove any exiting applications?
		mTaskContainers.removeExistingAppTokensIfPossible();
		for (int i = getTaskDisplayAreaCount() - 1; i >= 0; --i) {
		getTaskDisplayAreaAt(i).removeExistingAppTokensIfPossible();
		}
		}

		@Override
		@@ -4475,7 +4503,9 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		}

		void assignStackOrdering() {
		mTaskContainers.assignStackOrdering(getPendingTransaction());
		for (int i = getTaskDisplayAreaCount() - 1; i >= 0; --i) {
		getTaskDisplayAreaAt(i).assignStackOrdering(getPendingTransaction());
		}
		}

		/**
		@@ -5002,13 +5032,15 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		\|\| windowingMode == WINDOWING_MODE_MULTI_WINDOW);
		}

		ActivityStack createStack(int windowingMode, int activityType, boolean onTop) {
		return mTaskContainers.createStack(windowingMode, activityType, onTop, null /* info */,
		null /* intent /, false / createdByOrganizer */);
		}

		@Nullable
		ActivityStack getFocusedStack() {
		return mTaskContainers.getFocusedStack();
		for (int i = getTaskDisplayAreaCount() - 1; i >= 0; --i) {
		final ActivityStack stack = getTaskDisplayAreaAt(i).getFocusedStack();
		if (stack != null) {
		return stack;
		}
		}
		return null;
		}

		/**
		@@ -5016,11 +5048,15 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		* ACTIVITY_TYPE_STANDARD or ACTIVITY_TYPE_UNDEFINED
		*/
		void removeStacksInWindowingModes(int... windowingModes) {
		mTaskContainers.removeStacksInWindowingModes(windowingModes);
		for (int i = getTaskDisplayAreaCount() - 1; i >= 0; --i) {
		getTaskDisplayAreaAt(i).removeStacksInWindowingModes(windowingModes);
		}
		}

		void removeStacksWithActivityTypes(int... activityTypes) {
		mTaskContainers.removeStacksWithActivityTypes(activityTypes);
		for (int i = getTaskDisplayAreaCount() - 1; i >= 0; --i) {
		getTaskDisplayAreaAt(i).removeStacksWithActivityTypes(activityTypes);
		}
		}

		ActivityRecord topRunningActivity() {
		@@ -5037,7 +5073,14 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		* @return The top running activity. {@code null} if none is available.
		*/
		ActivityRecord topRunningActivity(boolean considerKeyguardState) {
		return mTaskContainers.topRunningActivity(considerKeyguardState);
		for (int i = getTaskDisplayAreaCount() - 1; i >= 0; --i) {
		final ActivityRecord activity = getTaskDisplayAreaAt(i)
		.topRunningActivity(considerKeyguardState);
		if (activity != null) {
		return activity;
		}
		}
		return null;
		}

		boolean updateDisplayOverrideConfigurationLocked() {
		@@ -5149,7 +5192,7 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		// The display may be about to rotate seamlessly, and the animation of closing apps may
		// still animate in old rotation. So make sure the outdated animation won't show on the
		// rotated display.
		mTaskContainers.forAllActivities(a -> {
		forAllActivities(a -> {
		if (a.nowVisible && a != mFixedRotationLaunchingApp
		&& a.getWindowConfiguration().getRotation() != newRotation) {
		final WindowContainer<?> w = a.getAnimatingContainer();
		@@ -5210,40 +5253,17 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo

		void remove() {
		mRemoving = true;
		final boolean destroyContentOnRemoval = shouldDestroyContentOnRemove();
		ActivityStack lastReparentedStack = null;
		mTaskContainers.mPreferredTopFocusableStack = null;

		// Stacks could be reparented from the removed display to other display. While
		// reparenting the last stack of the removed display, the remove display is ready to be
		// released (no more ActivityStack). But, we cannot release it at that moment or the
		// related WindowContainer will also be removed. So, we set display as removed after
		// reparenting stack finished.
		final TaskDisplayArea toTaskDisplayArea = mRootWindowContainer.getDefaultTaskDisplayArea();

		mRootWindowContainer.mStackSupervisor.beginDeferResume();
		try {
		int numStacks = getStackCount();
		// Keep the order from bottom to top.
		for (int stackNdx = 0; stackNdx < numStacks; stackNdx++) {
		final ActivityStack stack = getStackAt(stackNdx);
		// Always finish non-standard type stacks.
		if (destroyContentOnRemoval \|\| !stack.isActivityTypeStandardOrUndefined()) {
		stack.finishAllActivitiesImmediately();
		} else {
		// If default display is in split-window mode, set windowing mode of the stack
		// to split-screen secondary. Otherwise, set the windowing mode to undefined by
		// default to let stack inherited the windowing mode from the new display.
		final int windowingMode = toTaskDisplayArea.isSplitScreenModeActivated()
		? WINDOWING_MODE_SPLIT_SCREEN_SECONDARY
		: WINDOWING_MODE_UNDEFINED;
		stack.reparent(toTaskDisplayArea, true /* onTop */);
		stack.setWindowingMode(windowingMode);
		lastReparentedStack = stack;
		}
		// Stacks may be removed from this display. Ensure each stack will be processed and
		// the loop will end.
		stackNdx -= numStacks - getStackCount();
		numStacks = getStackCount();
		int numTaskContainers = getTaskDisplayAreaCount();
		for (int tdaNdx = 0; tdaNdx < numTaskContainers; tdaNdx++) {
		final ActivityStack lastReparentedStackFromArea = getTaskDisplayAreaAt(tdaNdx)
		.remove();
		if (lastReparentedStackFromArea != null) {
		lastReparentedStack = lastReparentedStackFromArea;
		}
		}
		} finally {
		mRootWindowContainer.mStackSupervisor.endDeferResume();
		@@ -5270,12 +5290,27 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		return;
		}

		final ActivityStack stack = getStackCount() == 1 ? getStackAt(0) : null;
		if (stack != null && stack.isActivityTypeHome() && !stack.hasChild()) {
		// Release this display if an empty home stack is the only thing left.
		// Since it is the last stack, this display will be released along with the stack
		// removal.
		stack.removeIfPossible();
		// Check if all task display areas have only the empty home stacks left.
		boolean onlyEmptyHomeStacksLeft = true;
		for (int tdaNdx = getTaskDisplayAreaCount() - 1; tdaNdx >= 0; --tdaNdx) {
		final TaskDisplayArea taskDisplayArea = getTaskDisplayAreaAt(tdaNdx);
		if (taskDisplayArea.getStackCount() != 1) {
		onlyEmptyHomeStacksLeft = false;
		break;
		}
		final ActivityStack stack = taskDisplayArea.getStackAt(0);
		if (!stack.isActivityTypeHome() \|\| stack.hasChild()) {
		onlyEmptyHomeStacksLeft = false;
		break;
		}
		}
		if (onlyEmptyHomeStacksLeft) {
		// Release this display if only empty home stack(s) are left. This display will be
		// released along with the stack(s) removal.
		for (int tdaNdx = getTaskDisplayAreaCount() - 1; tdaNdx >= 0; --tdaNdx) {
		final ActivityStack s = getTaskDisplayAreaAt(tdaNdx).getStackAt(0);
		s.removeIfPossible();
		}
		} else if (getTopStack() == null) {
		removeIfPossible();
		mRootWindowContainer.mStackSupervisor
		@@ -5334,10 +5369,9 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo

		void ensureActivitiesVisible(ActivityRecord starting, int configChanges,
		boolean preserveWindows, boolean notifyClients) {
		for (int stackNdx = getStackCount() - 1; stackNdx >= 0; --stackNdx) {
		final ActivityStack stack = getStackAt(stackNdx);
		stack.ensureActivitiesVisible(starting, configChanges, preserveWindows,
		notifyClients);
		for (int i = getTaskDisplayAreaCount() - 1; i >= 0; --i) {
		getTaskDisplayAreaAt(i).ensureActivitiesVisible(starting, configChanges,
		preserveWindows, notifyClients);
		}
		}

		@@ -5350,13 +5384,18 @@ class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowCo
		}

		void setDisplayToSingleTaskInstance() {
		final int childCount = getStackCount();
		if (childCount > 1) {
		final int taskDisplayAreaCount = getTaskDisplayAreaCount();
		if (taskDisplayAreaCount > 1) {
		throw new IllegalArgumentException(
		"Display already has multiple task display areas. display=" + this);
		}
		final int stackCount = getDefaultTaskDisplayArea().getStackCount();
		if (stackCount > 1) {
		throw new IllegalArgumentException("Display already has multiple stacks. display="
		+ this);
		}
		if (childCount > 0) {
		final ActivityStack stack = getStackAt(0);
		if (stackCount > 0) {
		final ActivityStack stack = getDefaultTaskDisplayArea().getStackAt(0);
		if (stack.getChildCount() > 1) {
		throw new IllegalArgumentException("Display stack already has multiple tasks."
		+ " display=" + this + " stack=" + stack);