Replace tasks in the same split with the dropping app

When launching a new app into a specific split, evicts all child tasks
that were originally in the same split.

Fix: 202739668
Test: atest WMShellUnitTests
Test: manual check dropping an app to a specific split evicts other
      tasks in the same split.
Change-Id: I3f52a3675d6ead742f0b75c83393462e5778a524

libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/SplitScreenController.java

@@ -16,6 +16,8 @@
 
 package com.android.wm.shell.splitscreen;
 
+import static android.app.ActivityManager.START_SUCCESS;
+import static android.app.ActivityManager.START_TASK_TO_FRONT;
 import static android.view.Display.DEFAULT_DISPLAY;
 import static android.view.RemoteAnimationTarget.MODE_OPENING;
 
@@ -213,7 +215,11 @@ public class SplitScreenController implements DragAndDropPolicy.Starter,
         options = mStageCoordinator.resolveStartStage(stage, position, options, null /* wct */);
 
         try {
-            ActivityTaskManager.getService().startActivityFromRecents(taskId, options);
+            final int result =
+                    ActivityTaskManager.getService().startActivityFromRecents(taskId, options);
+            if (result == START_SUCCESS || result == START_TASK_TO_FRONT) {
+                mStageCoordinator.evictOccludedChildren(position);
+            }
         } catch (RemoteException e) {
             Slog.e(TAG, "Failed to launch task", e);
         }
@@ -229,6 +235,7 @@ public class SplitScreenController implements DragAndDropPolicy.Starter,
                     mContext.getSystemService(LauncherApps.class);
             launcherApps.startShortcut(packageName, shortcutId, null /* sourceBounds */,
                     options, user);
+            mStageCoordinator.evictOccludedChildren(position);
         } catch (ActivityNotFoundException e) {
             Slog.e(TAG, "Failed to launch shortcut", e);
         }
@@ -272,6 +279,10 @@ public class SplitScreenController implements DragAndDropPolicy.Starter,
                         Slog.e(TAG, "Error finishing legacy transition: ", e);
                     }
                 }
+
+                // Launching a new app into a specific split evicts tasks previously in the same
+                // split.
+                mStageCoordinator.evictOccludedChildren(position);
             }
         };
         WindowContainerTransaction wct = new WindowContainerTransaction();

libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageCoordinator.java

@@ -394,6 +394,12 @@ class StageCoordinator implements SplitLayout.SplitLayoutHandler,
                 TRANSIT_SPLIT_SCREEN_OPEN_TO_SIDE, wct, remoteTransition, this);
     }
 
+    void evictOccludedChildren(@SplitPosition int position) {
+        final WindowContainerTransaction wct = new WindowContainerTransaction();
+        (position == mSideStagePosition ? mSideStage : mMainStage).evictOccludedChildren(wct);
+        mTaskOrganizer.applyTransaction(wct);
+    }
+
     Bundle resolveStartStage(@SplitScreen.StageType int stage,
             @SplitPosition int position, @androidx.annotation.Nullable Bundle options,
             @androidx.annotation.Nullable WindowContainerTransaction wct) {

libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageTaskListener.java

@@ -68,6 +68,7 @@ class StageTaskListener implements ShellTaskOrganizer.TaskListener {
         void onChildTaskStatusChanged(int taskId, boolean present, boolean visible);
 
         void onRootTaskVanished();
+
         void onNoLongerSupportMultiWindow();
     }
 
@@ -247,6 +248,15 @@ class StageTaskListener implements ShellTaskOrganizer.TaskListener {
         wct.reorder(mChildrenTaskInfo.get(taskId).token, onTop /* onTop */);
     }
 
+    void evictOccludedChildren(WindowContainerTransaction wct) {
+        for (int i = mChildrenTaskInfo.size() - 1; i >= 0; i--) {
+            final ActivityManager.RunningTaskInfo taskInfo = mChildrenTaskInfo.valueAt(i);
+            if (!taskInfo.isVisible) {
+                wct.reparent(taskInfo.token, null /* parent */, false /* onTop */);
+            }
+        }
+    }
+
     void setVisibility(boolean visible, WindowContainerTransaction wct) {
         wct.reorder(mRootTaskInfo.token, visible /* onTop */);
     }