Desktop windowing wallpaper

* Add translucent wallpaper activity to move Launcher in the correct
  state
* Handle back navigation to remove the wallpaper activity if the last
  freeform window is removed
* Handle window decoration close to remove wallpaper activity if the
  last window is closed

Bug: 309014605
Flag: ACONFIG com.android.window.flags.enable_desktop_windowing_wallpaper_activity DEVELOPMENT
Test: atest DesktopTasksControllerTest DesktopModeTaskRepositoryTest
Change-Id: I38271dc3903ec35d53b4607f034b27d8390ac839
diff --git a/libs/WindowManager/Shell/AndroidManifest.xml b/libs/WindowManager/Shell/AndroidManifest.xml
index 36d3313..7a98683 100644
--- a/libs/WindowManager/Shell/AndroidManifest.xml
+++ b/libs/WindowManager/Shell/AndroidManifest.xml
@@ -23,4 +23,12 @@
     <uses-permission android:name="android.permission.ROTATE_SURFACE_FLINGER" />
     <uses-permission android:name="android.permission.WAKEUP_SURFACE_FLINGER" />
     <uses-permission android:name="android.permission.READ_FRAME_BUFFER" />
+
+    <application>
+        <activity
+            android:name=".desktopmode.DesktopWallpaperActivity"
+            android:excludeFromRecents="true"
+            android:launchMode="singleInstance"
+            android:theme="@style/DesktopWallpaperTheme" />
+    </application>
 </manifest>
diff --git a/libs/WindowManager/Shell/res/values/styles.xml b/libs/WindowManager/Shell/res/values/styles.xml
index 08c2a02..13c0e66 100644
--- a/libs/WindowManager/Shell/res/values/styles.xml
+++ b/libs/WindowManager/Shell/res/values/styles.xml
@@ -23,6 +23,14 @@
         <item name="android:windowAnimationStyle">@style/Animation.ForcedResizable</item>
     </style>
 
+    <!-- Theme used for the activity that shows below the desktop mode windows to show wallpaper -->
+    <style name="DesktopWallpaperTheme" parent="@android:style/Theme.Wallpaper.NoTitleBar">
+        <item name="android:statusBarColor">@android:color/transparent</item>
+        <item name="android:navigationBarColor">@android:color/transparent</item>
+        <item name="android:windowDrawsSystemBarBackgrounds">true</item>
+        <item name="android:windowAnimationStyle">@null</item>
+    </style>
+
     <style name="Animation.ForcedResizable" parent="@android:style/Animation">
         <item name="android:activityOpenEnterAnimation">@anim/forced_resizable_enter</item>
 
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java b/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java
index b933e5d..7b64273 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java
@@ -59,6 +59,7 @@
 import com.android.wm.shell.desktopmode.DesktopModeStatus;
 import com.android.wm.shell.desktopmode.DesktopModeTaskRepository;
 import com.android.wm.shell.desktopmode.DesktopTasksController;
+import com.android.wm.shell.desktopmode.DesktopTasksTransitionObserver;
 import com.android.wm.shell.desktopmode.DragToDesktopTransitionHandler;
 import com.android.wm.shell.desktopmode.EnterDesktopTaskTransitionHandler;
 import com.android.wm.shell.desktopmode.ExitDesktopTaskTransitionHandler;
@@ -568,6 +569,18 @@
 
     @WMSingleton
     @Provides
+    static Optional<DesktopTasksTransitionObserver> provideDesktopTasksTransitionObserver(
+            Optional<DesktopModeTaskRepository> desktopModeTaskRepository,
+            Transitions transitions,
+            ShellInit shellInit
+    ) {
+        return desktopModeTaskRepository.flatMap(repository ->
+                Optional.of(new DesktopTasksTransitionObserver(repository, transitions, shellInit))
+        );
+    }
+
+    @WMSingleton
+    @Provides
     static DesktopModeLoggerTransitionObserver provideDesktopModeLoggerTransitionObserver(
             ShellInit shellInit,
             Transitions transitions,
@@ -622,7 +635,8 @@
     @Provides
     static Object provideIndependentShellComponentsToCreate(
             DragAndDropController dragAndDropController,
-            DefaultMixedHandler defaultMixedHandler) {
+            DefaultMixedHandler defaultMixedHandler,
+            Optional<DesktopTasksTransitionObserver> desktopTasksTransitionObserverOptional) {
         return new Object();
     }
 }
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepository.kt b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepository.kt
index 120d681..50cea01 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepository.kt
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepository.kt
@@ -22,6 +22,7 @@
 import android.util.ArraySet
 import android.util.SparseArray
 import android.view.Display.INVALID_DISPLAY
+import android.window.WindowContainerToken
 import androidx.core.util.forEach
 import androidx.core.util.keyIterator
 import androidx.core.util.valueIterator
@@ -49,6 +50,8 @@
         var stashed: Boolean = false
     )
 
+    // Token of the current wallpaper activity, used to remove it when the last task is removed
+    var wallpaperActivityToken: WindowContainerToken? = null
     // Tasks currently in freeform mode, ordered from top to bottom (top is at index 0).
     private val freeformTasksInZOrder = mutableListOf<Int>()
     private val activeTasksListeners = ArraySet<ActiveTasksListener>()
@@ -200,6 +203,15 @@
     }
 
     /**
+     *  Check if a task with the given [taskId] is the only active task on its display
+     */
+    fun isOnlyActiveTask(taskId: Int): Boolean {
+        return displayData.valueIterator().asSequence().any { data ->
+            data.activeTasks.singleOrNull() == taskId
+        }
+    }
+
+    /**
      * Get a set of the active tasks for given [displayId]
      */
     fun getActiveTasks(displayId: Int): ArraySet<Int> {
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksController.kt b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksController.kt
index 58942ec..5493f10 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksController.kt
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksController.kt
@@ -40,6 +40,7 @@
 import android.view.WindowManager.TRANSIT_CHANGE
 import android.view.WindowManager.TRANSIT_NONE
 import android.view.WindowManager.TRANSIT_OPEN
+import android.view.WindowManager.TRANSIT_TO_BACK
 import android.view.WindowManager.TRANSIT_TO_FRONT
 import android.window.RemoteTransition
 import android.window.TransitionInfo
@@ -381,7 +382,6 @@
         )
         val wct = WindowContainerTransaction()
         exitSplitIfApplicable(wct, taskInfo)
-        moveHomeTaskToFront(wct)
         bringDesktopAppsToFront(taskInfo.displayId, wct)
         addMoveToDesktopChanges(wct, taskInfo)
         wct.setBounds(taskInfo.token, freeformBounds)
@@ -401,6 +401,22 @@
         shellTaskOrganizer.applyTransaction(wct)
     }
 
+    /**
+     * Perform clean up of the desktop wallpaper activity if the closed window task is
+     * the last active task.
+     *
+     * @param wct transaction to modify if the last active task is closed
+     * @param taskId task id of the window that's being closed
+     */
+    fun onDesktopWindowClose(
+        wct: WindowContainerTransaction,
+        taskId: Int
+    ) {
+        if (desktopModeTaskRepository.isOnlyActiveTask(taskId)) {
+            removeWallpaperActivity(wct)
+        }
+    }
+
     /** Move a task with given `taskId` to fullscreen */
     fun moveToFullscreen(taskId: Int) {
         shellTaskOrganizer.getRunningTaskInfo(taskId)?.let { task ->
@@ -680,9 +696,15 @@
         KtProtoLog.v(WM_SHELL_DESKTOP_MODE, "DesktopTasksController: bringDesktopAppsToFront")
         val activeTasks = desktopModeTaskRepository.getActiveTasks(displayId)
 
-        // First move home to front and then other tasks on top of it
-        moveHomeTaskToFront(wct)
+        if (Flags.enableDesktopWindowingWallpaperActivity()) {
+            // Add translucent wallpaper activity to show the wallpaper underneath
+            addWallpaperActivity(wct)
+        } else {
+            // Move home to front
+            moveHomeTaskToFront(wct)
+        }
 
+        // Then move other tasks on top of it
         val allTasksInZOrder = desktopModeTaskRepository.getFreeformTasksInZOrder()
         activeTasks
             // Sort descending as the top task is at index 0. It should be ordered to top last
@@ -698,6 +720,26 @@
             ?.let { homeTask -> wct.reorder(homeTask.getToken(), true /* onTop */) }
     }
 
+    private fun addWallpaperActivity(wct: WindowContainerTransaction) {
+        KtProtoLog.v(WM_SHELL_DESKTOP_MODE, "DesktopTasksController: addWallpaper")
+        val intent = Intent(context, DesktopWallpaperActivity::class.java)
+        val options = ActivityOptions.makeBasic().apply {
+            isPendingIntentBackgroundActivityLaunchAllowedByPermission = true
+            pendingIntentBackgroundActivityStartMode =
+                ActivityOptions.MODE_BACKGROUND_ACTIVITY_START_ALLOWED
+        }
+        val pendingIntent = PendingIntent.getActivity(context, /* requestCode = */ 0, intent,
+            PendingIntent.FLAG_IMMUTABLE)
+        wct.sendPendingIntent(pendingIntent, intent, options.toBundle())
+    }
+
+    private fun removeWallpaperActivity(wct: WindowContainerTransaction) {
+        desktopModeTaskRepository.wallpaperActivityToken?.let { token ->
+            KtProtoLog.v(WM_SHELL_DESKTOP_MODE, "DesktopTasksController: removeWallpaper")
+            wct.removeTask(token)
+        }
+    }
+
     fun releaseVisualIndicator() {
         val t = SurfaceControl.Transaction()
         visualIndicator?.releaseVisualIndicator(t)
@@ -745,6 +787,9 @@
                     reason = "recents animation is running"
                     false
                 }
+                // Handle back navigation for the last window if wallpaper available
+                shouldRemoveWallpaper(request) ->
+                    true
                 // Only handle open or to front transitions
                 request.type != TRANSIT_OPEN && request.type != TRANSIT_TO_FRONT -> {
                     reason = "transition type not handled (${request.type})"
@@ -781,6 +826,7 @@
 
         val result = triggerTask?.let { task ->
             when {
+                request.type == TRANSIT_TO_BACK -> handleBackNavigation(task)
                 // If display has tasks stashed, handle as stashed launch
                 task.isStashed -> handleStashedTaskLaunch(task)
                 // Check if the task has a top transparent activity
@@ -828,6 +874,14 @@
         return Flags.enableDesktopWindowingModalsPolicy() && isSingleTopActivityTranslucent(task)
     }
 
+    private fun shouldRemoveWallpaper(request: TransitionRequestInfo): Boolean {
+        return Flags.enableDesktopWindowingWallpaperActivity() &&
+                request.type == TRANSIT_TO_BACK &&
+                request.triggerTask?.let { task ->
+                    desktopModeTaskRepository.isOnlyActiveTask(task.taskId)
+                } ?: false
+    }
+
     private fun handleFreeformTaskLaunch(task: RunningTaskInfo): WindowContainerTransaction? {
         KtProtoLog.v(WM_SHELL_DESKTOP_MODE, "DesktopTasksController: handleFreeformTaskLaunch")
         val activeTasks = desktopModeTaskRepository.getActiveTasks(task.displayId)
@@ -885,6 +939,19 @@
         }
     }
 
+    /** Handle back navigation by removing wallpaper activity if it's the last active task */
+    private fun handleBackNavigation(task: RunningTaskInfo): WindowContainerTransaction? {
+        if (desktopModeTaskRepository.isOnlyActiveTask(task.taskId) &&
+            desktopModeTaskRepository.wallpaperActivityToken != null) {
+            // Remove wallpaper activity when the last active task is removed
+            return WindowContainerTransaction().also { wct ->
+                removeWallpaperActivity(wct)
+            }
+        } else {
+            return null
+        }
+    }
+
     private fun addMoveToDesktopChanges(
         wct: WindowContainerTransaction,
         taskInfo: RunningTaskInfo
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksTransitionObserver.kt b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksTransitionObserver.kt
new file mode 100644
index 0000000..20df264
--- /dev/null
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksTransitionObserver.kt
@@ -0,0 +1,92 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.wm.shell.desktopmode
+
+import android.os.IBinder
+import android.view.SurfaceControl
+import android.view.WindowManager
+import android.window.TransitionInfo
+import com.android.window.flags.Flags.enableDesktopWindowingWallpaperActivity
+import com.android.wm.shell.protolog.ShellProtoLogGroup.WM_SHELL_DESKTOP_MODE
+import com.android.wm.shell.sysui.ShellInit
+import com.android.wm.shell.transition.Transitions
+import com.android.wm.shell.util.KtProtoLog
+
+/**
+ * A [Transitions.TransitionObserver] that observes shell transitions and updates
+ * the [DesktopModeTaskRepository] state TODO: b/332682201
+ * This observes transitions related to desktop mode
+ * and other transitions that originate both within and outside shell.
+ */
+class DesktopTasksTransitionObserver(
+    private val desktopModeTaskRepository: DesktopModeTaskRepository,
+    private val transitions: Transitions,
+    shellInit: ShellInit
+) : Transitions.TransitionObserver {
+
+    init {
+        if (Transitions.ENABLE_SHELL_TRANSITIONS && DesktopModeStatus.isEnabled()) {
+            shellInit.addInitCallback(::onInit, this)
+        }
+    }
+
+    fun onInit() {
+        KtProtoLog.d(WM_SHELL_DESKTOP_MODE, "DesktopTasksTransitionObserver: onInit")
+        transitions.registerObserver(this)
+    }
+
+    override fun onTransitionReady(
+        transition: IBinder,
+        info: TransitionInfo,
+        startTransaction: SurfaceControl.Transaction,
+        finishTransaction: SurfaceControl.Transaction
+    ) {
+        // TODO: b/332682201 Update repository state
+        updateWallpaperToken(info)
+    }
+
+    override fun onTransitionStarting(transition: IBinder) {
+        // TODO: b/332682201 Update repository state
+    }
+
+    override fun onTransitionMerged(merged: IBinder, playing: IBinder) {
+        // TODO: b/332682201 Update repository state
+    }
+
+    override fun onTransitionFinished(transition: IBinder, aborted: Boolean) {
+        // TODO: b/332682201 Update repository state
+    }
+
+    private fun updateWallpaperToken(info: TransitionInfo) {
+        if (!enableDesktopWindowingWallpaperActivity()) {
+            return
+        }
+        info.changes.forEach { change ->
+            change.taskInfo?.let { taskInfo ->
+                if (DesktopWallpaperActivity.isWallpaperTask(taskInfo)) {
+                    when (change.mode) {
+                        WindowManager.TRANSIT_OPEN ->
+                            desktopModeTaskRepository.wallpaperActivityToken = taskInfo.token
+                        WindowManager.TRANSIT_CLOSE ->
+                            desktopModeTaskRepository.wallpaperActivityToken = null
+                        else -> {}
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopWallpaperActivity.kt b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopWallpaperActivity.kt
new file mode 100644
index 0000000..c4a4474
--- /dev/null
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopWallpaperActivity.kt
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.wm.shell.desktopmode
+
+import android.app.Activity
+import android.app.ActivityManager
+import android.content.ComponentName
+import android.os.Bundle
+import android.view.WindowManager
+import com.android.wm.shell.protolog.ShellProtoLogGroup.WM_SHELL_DESKTOP_MODE
+import com.android.wm.shell.util.KtProtoLog
+
+/**
+ * A transparent activity used in the desktop mode to show the wallpaper under the freeform windows.
+ * This activity will be running in `FULLSCREEN` windowing mode, which ensures it hides Launcher.
+ * When entering desktop, we would ensure that it's added behind desktop apps and removed when
+ * leaving the desktop mode.
+ *
+ * Note! This activity should NOT interact directly with any other code in the Shell without calling
+ * onto the shell main thread. Activities are always started on the main thread.
+ */
+class DesktopWallpaperActivity : Activity() {
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        KtProtoLog.d(WM_SHELL_DESKTOP_MODE, "DesktopWallpaperActivity: onCreate")
+        super.onCreate(savedInstanceState)
+        window.addFlags(WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE)
+    }
+
+    companion object {
+        private const val SYSTEM_UI_PACKAGE_NAME = "com.android.systemui"
+        private val wallpaperActivityComponent =
+            ComponentName(SYSTEM_UI_PACKAGE_NAME, DesktopWallpaperActivity::class.java.name)
+
+        @JvmStatic
+        fun isWallpaperTask(taskInfo: ActivityManager.RunningTaskInfo) =
+            taskInfo.baseIntent.component?.let(::isWallpaperComponent) ?: false
+
+        @JvmStatic
+        fun isWallpaperComponent(component: ComponentName) =
+            component == wallpaperActivityComponent
+    }
+}
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/transition/HomeTransitionObserver.java b/libs/WindowManager/Shell/src/com/android/wm/shell/transition/HomeTransitionObserver.java
index c9185ae..b1a1e59 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/transition/HomeTransitionObserver.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/transition/HomeTransitionObserver.java
@@ -20,6 +20,7 @@
 import static android.view.Display.DEFAULT_DISPLAY;
 import static android.window.TransitionInfo.FLAG_BACK_GESTURE_ANIMATED;
 
+import static com.android.wm.shell.transition.Transitions.TRANSIT_DESKTOP_MODE_START_DRAG_TO_DESKTOP;
 import static com.android.wm.shell.transition.Transitions.TransitionObserver;
 
 import android.annotation.NonNull;
@@ -60,7 +61,8 @@
             @NonNull SurfaceControl.Transaction finishTransaction) {
         for (TransitionInfo.Change change : info.getChanges()) {
             final ActivityManager.RunningTaskInfo taskInfo = change.getTaskInfo();
-            if (taskInfo == null
+            if (info.getType() == TRANSIT_DESKTOP_MODE_START_DRAG_TO_DESKTOP
+                    || taskInfo == null
                     || taskInfo.displayId != DEFAULT_DISPLAY
                     || taskInfo.taskId == -1
                     || !taskInfo.isRunning) {
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecorViewModel.java b/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecorViewModel.java
index a0f9c6b..2f96914 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecorViewModel.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecorViewModel.java
@@ -84,6 +84,7 @@
 import com.android.wm.shell.desktopmode.DesktopModeVisualIndicator;
 import com.android.wm.shell.desktopmode.DesktopTasksController;
 import com.android.wm.shell.desktopmode.DesktopTasksController.SnapPosition;
+import com.android.wm.shell.desktopmode.DesktopWallpaperActivity;
 import com.android.wm.shell.freeform.FreeformTaskTransitionStarter;
 import com.android.wm.shell.splitscreen.SplitScreen;
 import com.android.wm.shell.splitscreen.SplitScreen.StageType;
@@ -407,7 +408,9 @@
                     mSplitScreenController.moveTaskToFullscreen(getOtherSplitTask(mTaskId).taskId,
                             SplitScreenController.EXIT_REASON_DESKTOP_MODE);
                 } else {
-                    mTaskOperations.closeTask(mTaskToken);
+                    WindowContainerTransaction wct = new WindowContainerTransaction();
+                    mDesktopTasksController.onDesktopWindowClose(wct, mTaskId);
+                    mTaskOperations.closeTask(mTaskToken, wct);
                 }
             } else if (id == R.id.back_button) {
                 mTaskOperations.injectBackKey();
@@ -1025,6 +1028,7 @@
             return false;
         }
         return DesktopModeStatus.isEnabled()
+                && !DesktopWallpaperActivity.isWallpaperTask(taskInfo)
                 && taskInfo.getWindowingMode() != WINDOWING_MODE_PINNED
                 && taskInfo.getActivityType() == ACTIVITY_TYPE_STANDARD
                 && !taskInfo.configuration.windowConfiguration.isAlwaysOnTop()
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/TaskOperations.java b/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/TaskOperations.java
index d0fcd86..2821f81 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/TaskOperations.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/TaskOperations.java
@@ -72,7 +72,10 @@
     }
 
     void closeTask(WindowContainerToken taskToken) {
-        WindowContainerTransaction wct = new WindowContainerTransaction();
+        closeTask(taskToken, new WindowContainerTransaction());
+    }
+
+    void closeTask(WindowContainerToken taskToken, WindowContainerTransaction wct) {
         wct.removeTask(taskToken);
         if (Transitions.ENABLE_SHELL_TRANSITIONS) {
             mTransitionStarter.startRemoveTransition(wct);
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/TestRunningTaskInfoBuilder.java b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/TestRunningTaskInfoBuilder.java
index 3672ae3..24f4d92 100644
--- a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/TestRunningTaskInfoBuilder.java
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/TestRunningTaskInfoBuilder.java
@@ -23,8 +23,10 @@
 import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.mock;
 
+import android.annotation.NonNull;
 import android.app.ActivityManager;
 import android.app.WindowConfiguration;
+import android.content.Intent;
 import android.graphics.Point;
 import android.graphics.Rect;
 import android.os.IBinder;
@@ -38,6 +40,7 @@
 
     private WindowContainerToken mToken = createMockWCToken();
     private int mParentTaskId = INVALID_TASK_ID;
+    private Intent mBaseIntent = new Intent();
     private @WindowConfiguration.ActivityType int mActivityType = ACTIVITY_TYPE_STANDARD;
     private @WindowConfiguration.WindowingMode int mWindowingMode = WINDOWING_MODE_UNDEFINED;
     private int mDisplayId = Display.DEFAULT_DISPLAY;
@@ -68,6 +71,15 @@
         return this;
     }
 
+    /**
+     * Set {@link ActivityManager.RunningTaskInfo#baseIntent} for the task info, by default
+     * an empty intent is assigned
+     */
+    public TestRunningTaskInfoBuilder setBaseIntent(@NonNull Intent intent) {
+        mBaseIntent = intent;
+        return this;
+    }
+
     public TestRunningTaskInfoBuilder setActivityType(
             @WindowConfiguration.ActivityType int activityType) {
         mActivityType = activityType;
@@ -109,6 +121,7 @@
     public ActivityManager.RunningTaskInfo build() {
         final ActivityManager.RunningTaskInfo info = new ActivityManager.RunningTaskInfo();
         info.taskId = sNextTaskId++;
+        info.baseIntent = mBaseIntent;
         info.parentTaskId = mParentTaskId;
         info.displayId = mDisplayId;
         info.configuration.windowConfiguration.setBounds(mBounds);
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepositoryTest.kt b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepositoryTest.kt
index 0c45d52..b2b54ac 100644
--- a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepositoryTest.kt
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepositoryTest.kt
@@ -119,6 +119,57 @@
     }
 
     @Test
+    fun isOnlyActiveTask_noActiveTasks() {
+        // Not an active task
+        assertThat(repo.isOnlyActiveTask(1)).isFalse()
+    }
+
+    @Test
+    fun isOnlyActiveTask_singleActiveTask() {
+        repo.addActiveTask(DEFAULT_DISPLAY, 1)
+        // The only active task
+        assertThat(repo.isActiveTask(1)).isTrue()
+        assertThat(repo.isOnlyActiveTask(1)).isTrue()
+        // Not an active task
+        assertThat(repo.isActiveTask(99)).isFalse()
+        assertThat(repo.isOnlyActiveTask(99)).isFalse()
+    }
+
+    @Test
+    fun isOnlyActiveTask_multipleActiveTasks() {
+        repo.addActiveTask(DEFAULT_DISPLAY, 1)
+        repo.addActiveTask(DEFAULT_DISPLAY, 2)
+        // Not the only task
+        assertThat(repo.isActiveTask(1)).isTrue()
+        assertThat(repo.isOnlyActiveTask(1)).isFalse()
+        // Not the only task
+        assertThat(repo.isActiveTask(2)).isTrue()
+        assertThat(repo.isOnlyActiveTask(2)).isFalse()
+        // Not an active task
+        assertThat(repo.isActiveTask(99)).isFalse()
+        assertThat(repo.isOnlyActiveTask(99)).isFalse()
+    }
+
+    @Test
+    fun isOnlyActiveTask_multipleDisplays() {
+        repo.addActiveTask(DEFAULT_DISPLAY, 1)
+        repo.addActiveTask(DEFAULT_DISPLAY, 2)
+        repo.addActiveTask(SECOND_DISPLAY, 3)
+        // Not the only task on DEFAULT_DISPLAY
+        assertThat(repo.isActiveTask(1)).isTrue()
+        assertThat(repo.isOnlyActiveTask(1)).isFalse()
+        // Not the only task on DEFAULT_DISPLAY
+        assertThat(repo.isActiveTask(2)).isTrue()
+        assertThat(repo.isOnlyActiveTask(2)).isFalse()
+        // The only active task on SECOND_DISPLAY
+        assertThat(repo.isActiveTask(3)).isTrue()
+        assertThat(repo.isOnlyActiveTask(3)).isTrue()
+        // Not an active task
+        assertThat(repo.isActiveTask(99)).isFalse()
+        assertThat(repo.isOnlyActiveTask(99)).isFalse()
+    }
+
+    @Test
     fun addListener_notifiesVisibleFreeformTask() {
         repo.updateVisibleFreeformTasks(DEFAULT_DISPLAY, taskId = 1, visible = true)
         val listener = TestVisibilityListener()
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopTasksControllerTest.kt b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopTasksControllerTest.kt
index 93a967e..07aaba5 100644
--- a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopTasksControllerTest.kt
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopTasksControllerTest.kt
@@ -23,10 +23,13 @@
 import android.app.WindowConfiguration.WINDOWING_MODE_FULLSCREEN
 import android.app.WindowConfiguration.WINDOWING_MODE_MULTI_WINDOW
 import android.app.WindowConfiguration.WINDOWING_MODE_UNDEFINED
+import android.content.Intent
 import android.graphics.Point
 import android.graphics.PointF
 import android.graphics.Rect
 import android.os.Binder
+import android.platform.test.annotations.DisableFlags
+import android.platform.test.annotations.EnableFlags
 import android.platform.test.flag.junit.SetFlagsRule
 import android.testing.AndroidTestingRunner
 import android.view.Display.DEFAULT_DISPLAY
@@ -34,11 +37,15 @@
 import android.view.WindowManager
 import android.view.WindowManager.TRANSIT_CHANGE
 import android.view.WindowManager.TRANSIT_OPEN
+import android.view.WindowManager.TRANSIT_TO_BACK
 import android.view.WindowManager.TRANSIT_TO_FRONT
 import android.window.DisplayAreaInfo
 import android.window.RemoteTransition
 import android.window.TransitionRequestInfo
+import android.window.WindowContainerToken
 import android.window.WindowContainerTransaction
+import android.window.WindowContainerTransaction.HierarchyOp.HIERARCHY_OP_TYPE_PENDING_INTENT
+import android.window.WindowContainerTransaction.HierarchyOp.HIERARCHY_OP_TYPE_REMOVE_TASK
 import android.window.WindowContainerTransaction.HierarchyOp.HIERARCHY_OP_TYPE_REORDER
 import androidx.test.filters.SmallTest
 import com.android.dx.mockito.inline.extended.ExtendedMockito.doReturn
@@ -219,7 +226,8 @@
     }
 
     @Test
-    fun showDesktopApps_allAppsInvisible_bringsToFront() {
+    @DisableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun showDesktopApps_allAppsInvisible_bringsToFront_desktopWallpaperDisabled() {
         val homeTask = setUpHomeTask()
         val task1 = setUpFreeformTask()
         val task2 = setUpFreeformTask()
@@ -238,7 +246,27 @@
     }
 
     @Test
-    fun showDesktopApps_appsAlreadyVisible_bringsToFront() {
+    @EnableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun showDesktopApps_allAppsInvisible_bringsToFront_desktopWallpaperEnabled() {
+        val task1 = setUpFreeformTask()
+        val task2 = setUpFreeformTask()
+        markTaskHidden(task1)
+        markTaskHidden(task2)
+
+        controller.showDesktopApps(DEFAULT_DISPLAY, RemoteTransition(TestRemoteTransition()))
+
+        val wct =
+            getLatestWct(type = TRANSIT_TO_FRONT, handlerClass = OneShotRemoteHandler::class.java)
+        assertThat(wct.hierarchyOps).hasSize(3)
+        // Expect order to be from bottom: wallpaper intent, task1, task2
+        wct.assertPendingIntentAt(index = 0, desktopWallpaperIntent)
+        wct.assertReorderAt(index = 1, task1)
+        wct.assertReorderAt(index = 2, task2)
+    }
+
+    @Test
+    @DisableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun showDesktopApps_appsAlreadyVisible_bringsToFront_desktopWallpaperDisabled() {
         val homeTask = setUpHomeTask()
         val task1 = setUpFreeformTask()
         val task2 = setUpFreeformTask()
@@ -257,7 +285,27 @@
     }
 
     @Test
-    fun showDesktopApps_someAppsInvisible_reordersAll() {
+    @EnableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun showDesktopApps_appsAlreadyVisible_bringsToFront_desktopWallpaperEnabled() {
+        val task1 = setUpFreeformTask()
+        val task2 = setUpFreeformTask()
+        markTaskVisible(task1)
+        markTaskVisible(task2)
+
+        controller.showDesktopApps(DEFAULT_DISPLAY, RemoteTransition(TestRemoteTransition()))
+
+        val wct =
+            getLatestWct(type = TRANSIT_TO_FRONT, handlerClass = OneShotRemoteHandler::class.java)
+        assertThat(wct.hierarchyOps).hasSize(3)
+        // Expect order to be from bottom: wallpaper intent, task1, task2
+        wct.assertPendingIntentAt(index = 0, desktopWallpaperIntent)
+        wct.assertReorderAt(index = 1, task1)
+        wct.assertReorderAt(index = 2, task2)
+    }
+
+    @Test
+    @DisableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun showDesktopApps_someAppsInvisible_reordersAll_desktopWallpaperDisabled() {
         val homeTask = setUpHomeTask()
         val task1 = setUpFreeformTask()
         val task2 = setUpFreeformTask()
@@ -276,7 +324,27 @@
     }
 
     @Test
-    fun showDesktopApps_noActiveTasks_reorderHomeToTop() {
+    @EnableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun showDesktopApps_someAppsInvisible_reordersAll_desktopWallpaperEnabled() {
+        val task1 = setUpFreeformTask()
+        val task2 = setUpFreeformTask()
+        markTaskHidden(task1)
+        markTaskVisible(task2)
+
+        controller.showDesktopApps(DEFAULT_DISPLAY, RemoteTransition(TestRemoteTransition()))
+
+        val wct =
+            getLatestWct(type = TRANSIT_TO_FRONT, handlerClass = OneShotRemoteHandler::class.java)
+        assertThat(wct.hierarchyOps).hasSize(3)
+        // Expect order to be from bottom: wallpaper intent, task1, task2
+        wct.assertPendingIntentAt(index = 0, desktopWallpaperIntent)
+        wct.assertReorderAt(index = 1, task1)
+        wct.assertReorderAt(index = 2, task2)
+    }
+
+    @Test
+    @DisableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun showDesktopApps_noActiveTasks_reorderHomeToTop_desktopWallpaperDisabled() {
         val homeTask = setUpHomeTask()
 
         controller.showDesktopApps(DEFAULT_DISPLAY, RemoteTransition(TestRemoteTransition()))
@@ -288,7 +356,18 @@
     }
 
     @Test
-    fun showDesktopApps_twoDisplays_bringsToFrontOnlyOneDisplay() {
+    @EnableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun showDesktopApps_noActiveTasks_addDesktopWallpaper_desktopWallpaperEnabled() {
+        controller.showDesktopApps(DEFAULT_DISPLAY, RemoteTransition(TestRemoteTransition()))
+
+        val wct =
+            getLatestWct(type = TRANSIT_TO_FRONT, handlerClass = OneShotRemoteHandler::class.java)
+        wct.assertPendingIntentAt(index = 0, desktopWallpaperIntent)
+    }
+
+    @Test
+    @DisableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun showDesktopApps_twoDisplays_bringsToFrontOnlyOneDisplay_desktopWallpaperDisabled() {
         val homeTaskDefaultDisplay = setUpHomeTask(DEFAULT_DISPLAY)
         val taskDefaultDisplay = setUpFreeformTask(DEFAULT_DISPLAY)
         setUpHomeTask(SECOND_DISPLAY)
@@ -307,6 +386,25 @@
     }
 
     @Test
+    @EnableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun showDesktopApps_twoDisplays_bringsToFrontOnlyOneDisplay_desktopWallpaperEnabled() {
+        val taskDefaultDisplay = setUpFreeformTask(DEFAULT_DISPLAY)
+        setUpHomeTask(SECOND_DISPLAY)
+        val taskSecondDisplay = setUpFreeformTask(SECOND_DISPLAY)
+        markTaskHidden(taskDefaultDisplay)
+        markTaskHidden(taskSecondDisplay)
+
+        controller.showDesktopApps(DEFAULT_DISPLAY, RemoteTransition(TestRemoteTransition()))
+
+        val wct =
+            getLatestWct(type = TRANSIT_TO_FRONT, handlerClass = OneShotRemoteHandler::class.java)
+        assertThat(wct.hierarchyOps).hasSize(2)
+        // Expect order to be from bottom: wallpaper intent, task
+        wct.assertPendingIntentAt(index = 0, desktopWallpaperIntent)
+        wct.assertReorderAt(index = 1, taskDefaultDisplay)
+    }
+
+    @Test
     fun getVisibleTaskCount_noTasks_returnsZero() {
         assertThat(controller.getVisibleTaskCount(DEFAULT_DISPLAY)).isEqualTo(0)
     }
@@ -413,7 +511,8 @@
     }
 
     @Test
-    fun moveToDesktop_otherFreeformTasksBroughtToFront() {
+    @DisableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun moveToDesktop_otherFreeformTasksBroughtToFront_desktopWallpaperDisabled() {
         val homeTask = setUpHomeTask()
         val freeformTask = setUpFreeformTask()
         val fullscreenTask = setUpFullscreenTask()
@@ -431,6 +530,26 @@
     }
 
     @Test
+    @EnableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun moveToDesktop_otherFreeformTasksBroughtToFront_desktopWallpaperEnabled() {
+        val freeformTask = setUpFreeformTask()
+        val fullscreenTask = setUpFullscreenTask()
+        markTaskHidden(freeformTask)
+
+        controller.moveToDesktop(fullscreenTask)
+
+        with(getLatestMoveToDesktopWct()) {
+            // Operations should include wallpaper intent, freeform task, fullscreen task
+            assertThat(hierarchyOps).hasSize(3)
+            assertPendingIntentAt(index = 0, desktopWallpaperIntent)
+            assertReorderAt(index = 1, freeformTask)
+            assertReorderAt(index = 2, fullscreenTask)
+            assertThat(changes[fullscreenTask.token.asBinder()]?.windowingMode)
+                .isEqualTo(WINDOWING_MODE_FREEFORM)
+        }
+    }
+
+    @Test
     fun moveToDesktop_onlyFreeformTasksFromCurrentDisplayBroughtToFront() {
         setUpHomeTask(displayId = DEFAULT_DISPLAY)
         val freeformTaskDefault = setUpFreeformTask(displayId = DEFAULT_DISPLAY)
@@ -595,6 +714,48 @@
     }
 
     @Test
+    fun onDesktopWindowClose_noActiveTasks() {
+        val wct = WindowContainerTransaction()
+        controller.onDesktopWindowClose(wct, 1 /* taskId */)
+        // Doesn't modify transaction
+        assertThat(wct.hierarchyOps).isEmpty()
+    }
+
+    @Test
+    fun onDesktopWindowClose_singleActiveTask_noWallpaperActivityToken() {
+        val task = setUpFreeformTask()
+        val wct = WindowContainerTransaction()
+        controller.onDesktopWindowClose(wct, task.taskId)
+        // Doesn't modify transaction
+        assertThat(wct.hierarchyOps).isEmpty()
+    }
+
+    @Test
+    fun onDesktopWindowClose_singleActiveTask_hasWallpaperActivityToken() {
+        val task = setUpFreeformTask()
+        val wallpaperToken = MockToken().token()
+        desktopModeTaskRepository.wallpaperActivityToken = wallpaperToken
+
+        val wct = WindowContainerTransaction()
+        controller.onDesktopWindowClose(wct, task.taskId)
+        // Adds remove wallpaper operation
+        wct.assertRemoveAt(index = 0, wallpaperToken)
+    }
+
+    @Test
+    fun onDesktopWindowClose_multipleActiveTasks() {
+        val task1 = setUpFreeformTask()
+        setUpFreeformTask()
+        val wallpaperToken = MockToken().token()
+        desktopModeTaskRepository.wallpaperActivityToken = wallpaperToken
+
+        val wct = WindowContainerTransaction()
+        controller.onDesktopWindowClose(wct, task1.taskId)
+        // Doesn't modify transaction
+        assertThat(wct.hierarchyOps).isEmpty()
+    }
+
+    @Test
     fun handleRequest_fullscreenTask_freeformVisible_returnSwitchToFreeformWCT() {
         assumeTrue(ENABLE_SHELL_TRANSITIONS)
 
@@ -638,6 +799,7 @@
     }
 
     @Test
+    @DisableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
     fun handleRequest_fullscreenTask_desktopStashed_returnWCTWithAllAppsBroughtToFront() {
         assumeTrue(ENABLE_SHELL_TRANSITIONS)
         whenever(DesktopModeStatus.isStashingEnabled()).thenReturn(true)
@@ -710,6 +872,7 @@
     }
 
     @Test
+    @DisableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
     fun handleRequest_freeformTask_desktopStashed_returnWCTWithAllAppsBroughtToFront() {
         assumeTrue(ENABLE_SHELL_TRANSITIONS)
         whenever(DesktopModeStatus.isStashingEnabled()).thenReturn(true)
@@ -796,6 +959,55 @@
     }
 
     @Test
+    @EnableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun handleRequest_backTransition_singleActiveTask_noToken() {
+        val task = setUpFreeformTask()
+        val result =
+            controller.handleRequest(Binder(), createTransition(task, type = TRANSIT_TO_BACK))
+        // Doesn't handle request
+        assertThat(result).isNull()
+    }
+
+    @Test
+    @DisableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun handleRequest_backTransition_singleActiveTask_hasToken_desktopWallpaperDisabled() {
+        desktopModeTaskRepository.wallpaperActivityToken = MockToken().token()
+
+        val task = setUpFreeformTask()
+        val result =
+            controller.handleRequest(Binder(), createTransition(task, type = TRANSIT_TO_BACK))
+        // Doesn't handle request
+        assertThat(result).isNull()
+    }
+
+    @Test
+    @EnableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun handleRequest_backTransition_singleActiveTask_hasToken_desktopWallpaperEnabled() {
+        val wallpaperToken = MockToken().token()
+        desktopModeTaskRepository.wallpaperActivityToken = wallpaperToken
+
+        val task = setUpFreeformTask()
+        val result =
+            controller.handleRequest(Binder(), createTransition(task, type = TRANSIT_TO_BACK))
+        assertThat(result).isNotNull()
+        // Creates remove wallpaper transaction
+        result!!.assertRemoveAt(index = 0, wallpaperToken)
+    }
+
+    @Test
+    @EnableFlags(Flags.FLAG_ENABLE_DESKTOP_WINDOWING_WALLPAPER_ACTIVITY)
+    fun handleRequest_backTransition_multipleActiveTasks() {
+        desktopModeTaskRepository.wallpaperActivityToken = MockToken().token()
+
+        val task1 = setUpFreeformTask()
+        setUpFreeformTask()
+        val result =
+            controller.handleRequest(Binder(), createTransition(task1, type = TRANSIT_TO_BACK))
+        // Doesn't handle request
+        assertThat(result).isNull()
+    }
+
+    @Test
     fun stashDesktopApps_stateUpdates() {
         whenever(DesktopModeStatus.isStashingEnabled()).thenReturn(true)
 
@@ -998,6 +1210,9 @@
         assertThat(desktopModeTaskRepository.removeBoundsBeforeMaximize(task.taskId)).isNull()
     }
 
+    private val desktopWallpaperIntent: Intent
+        get() = Intent(context, DesktopWallpaperActivity::class.java)
+
     private fun setUpFreeformTask(
             displayId: Int = DEFAULT_DISPLAY,
             bounds: Rect? = null
@@ -1123,10 +1338,14 @@
     }
 }
 
-private fun WindowContainerTransaction.assertReorderAt(index: Int, task: RunningTaskInfo) {
+private fun WindowContainerTransaction.assertIndexInBounds(index: Int) {
     assertWithMessage("WCT does not have a hierarchy operation at index $index")
         .that(hierarchyOps.size)
         .isGreaterThan(index)
+}
+
+private fun WindowContainerTransaction.assertReorderAt(index: Int, task: RunningTaskInfo) {
+    assertIndexInBounds(index)
     val op = hierarchyOps[index]
     assertThat(op.type).isEqualTo(HIERARCHY_OP_TYPE_REORDER)
     assertThat(op.container).isEqualTo(task.token.asBinder())
@@ -1137,3 +1356,17 @@
         assertReorderAt(i, tasks[i])
     }
 }
+
+private fun WindowContainerTransaction.assertRemoveAt(index: Int, token: WindowContainerToken) {
+    assertIndexInBounds(index)
+    val op = hierarchyOps[index]
+    assertThat(op.type).isEqualTo(HIERARCHY_OP_TYPE_REMOVE_TASK)
+    assertThat(op.container).isEqualTo(token.asBinder())
+}
+
+private fun WindowContainerTransaction.assertPendingIntentAt(index: Int, intent: Intent) {
+    assertIndexInBounds(index)
+    val op = hierarchyOps[index]
+    assertThat(op.type).isEqualTo(HIERARCHY_OP_TYPE_PENDING_INTENT)
+    assertThat(op.pendingIntent?.intent?.component).isEqualTo(intent.component)
+}
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/transition/HomeTransitionObserverTest.java b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/transition/HomeTransitionObserverTest.java
index e7d37ad..0db10ef 100644
--- a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/transition/HomeTransitionObserverTest.java
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/transition/HomeTransitionObserverTest.java
@@ -24,6 +24,7 @@
 import static android.window.TransitionInfo.FLAG_BACK_GESTURE_ANIMATED;
 
 import static com.android.dx.mockito.inline.extended.ExtendedMockito.verify;
+import static com.android.wm.shell.transition.Transitions.TRANSIT_DESKTOP_MODE_START_DRAG_TO_DESKTOP;
 
 import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.Mockito.mock;
@@ -167,6 +168,25 @@
     }
 
     @Test
+    public void testStartDragToDesktopDoesNotTriggerCallback() throws RemoteException {
+        TransitionInfo info = mock(TransitionInfo.class);
+        TransitionInfo.Change change = mock(TransitionInfo.Change.class);
+        ActivityManager.RunningTaskInfo taskInfo = mock(ActivityManager.RunningTaskInfo.class);
+        when(change.getTaskInfo()).thenReturn(taskInfo);
+        when(info.getChanges()).thenReturn(new ArrayList<>(List.of(change)));
+        when(info.getType()).thenReturn(TRANSIT_DESKTOP_MODE_START_DRAG_TO_DESKTOP);
+
+        setupTransitionInfo(taskInfo, change, ACTIVITY_TYPE_HOME, TRANSIT_OPEN, true);
+
+        mHomeTransitionObserver.onTransitionReady(mock(IBinder.class),
+                info,
+                mock(SurfaceControl.Transaction.class),
+                mock(SurfaceControl.Transaction.class));
+
+        verify(mListener, times(0)).onHomeVisibilityChanged(anyBoolean());
+    }
+
+    @Test
     public void testHomeActivityWithBackGestureNotifiesHomeIsVisible() throws RemoteException {
         TransitionInfo info = mock(TransitionInfo.class);
         TransitionInfo.Change change = mock(TransitionInfo.Change.class);