Fix WM shell crash when targets belong to a different display.

When showWhenLocked activity is launched on a second display, it's
possible that a window container for a wallpaper on the default display
and the showWhenLocked activity on the second display are both collected
for app transition.

This is a workaround to prevent NPE for such cases.

Bug: 260997053
Test: atest MultiDisplayLockedKeyguardTests
Change-Id: I9dbd0928aa785a6d547b8e19841748280ba982c9

1 files changed, 5 insertions, 2 deletions

diff --git a/services/core/java/com/android/server/wm/Transition.java b/services/core/java/com/android/server/wm/Transition.java
index ec3962c282f6..e90a52f774a1 100644
--- a/services/core/java/com/android/server/wm/Transition.java
+++ b/services/core/java/com/android/server/wm/Transition.java
@@ -1645,8 +1645,11 @@ class Transition implements BLASTSyncEngine.TransactionReadyListener {
 
         WindowContainer<?> ancestor = findCommonAncestor(sortedTargets, changes, topApp);
 
-        // make leash based on highest (z-order) direct child of ancestor with a participant.
-        WindowContainer leashReference = sortedTargets.get(0);
+        // Make leash based on highest (z-order) direct child of ancestor with a participant.
+        // TODO(b/261418859): Handle the case when the target contains window containers which
+        // belong to a different display. As a workaround we use topApp, from which wallpaper
+        // window container is removed, instead of sortedTargets here.
+        WindowContainer leashReference = topApp;
         while (leashReference.getParent() != ancestor) {
             leashReference = leashReference.getParent();
         }