Photo Gallery widget: fix NPE in getViewAt

Repro:
 - Add Photo Gallery widget to a home screen
 - Select "Shuffle all images"
 - Immediately drag widget to "Remove"
 - Observe NPE

The remote view is destroyed and the reference to mSource is null.
By making onDestroy and getViewAt synchronized methods, we ensure that
destroy cannot be executed to null out mSource while getViewAt is
being called.

Change-Id: I470f9f6227f437039cf111071c905268db1bd62e
(cherry picked from commit 9abe70951b1cc559f82bbf803a1f4893105c27c9)

1 files changed, 6 insertions, 2 deletions

diff --git a/src/com/android/gallery3d/gadget/WidgetService.java b/src/com/android/gallery3d/gadget/WidgetService.java
index fc54fb6e8..854433776 100644
--- a/src/com/android/gallery3d/gadget/WidgetService.java
+++ b/src/com/android/gallery3d/gadget/WidgetService.java
@@ -80,7 +80,7 @@ public class WidgetService extends RemoteViewsService {
         }
 
         @Override
-        public void onDestroy() {
+        public synchronized void onDestroy() {
             mSource.close();
             mSource = null;
         }
@@ -115,7 +115,11 @@ public class WidgetService extends RemoteViewsService {
         }
 
         @Override
-        public RemoteViews getViewAt(int position) {
+        public synchronized RemoteViews getViewAt(int position) {
+            if (mSource == null) {
+                // This instance has been destroyed, exit out
+                return null;
+            }
             Bitmap bitmap = mSource.getImage(position);
             if (bitmap == null) return getLoadingView();
             RemoteViews views = new RemoteViews(