fix intermittent crash in rotate-on-detail-view crash fix

Was sometimes crashing due to trying to remove observer too late
after detecting the newly loaded adapter. (Race condition?)

Change-Id: Ib62d78a2b7d863606070bf6d72ec37b9791bf243

Author: bvibber

commons/src/main/java/org/wikimedia/commons/contributions/ContributionsActivity.java

@@ -229,7 +229,7 @@ public void onLoadFinished(Loader cursorLoader, Object result) {
                 ((MediaListAdapter)contributionsList.getAdapter()).updateMediaList((ArrayList<Media>) result);
             }
         }
-        notifyAndClearDataSetObservers();
+        notifyAndMigrateDataSetObservers();
     }
 
     public void onLoaderReset(Loader cursorLoader) {
@@ -262,11 +262,19 @@ public void notifyDatasetChanged() {
         // Do nothing for now
     }
 
-    private void notifyAndClearDataSetObservers() {
+    private void notifyAndMigrateDataSetObservers() {
+        Adapter adapter = contributionsList.getAdapter();
+
+        // First, move the observers over to the adapter now that we have it.
         for (DataSetObserver observer : observersWaitingForLoad) {
-            observer.onChanged();
+            adapter.registerDataSetObserver(observer);
         }
         observersWaitingForLoad.clear();
+
+        // Now fire off a first notification...
+        for (DataSetObserver observer : observersWaitingForLoad) {
+            observer.onChanged();
+        }
     }
 
     public void registerDataSetObserver(DataSetObserver observer) {
@@ -283,7 +291,7 @@ public void unregisterDataSetObserver(DataSetObserver observer) {
         if (adapter == null) {
             observersWaitingForLoad.remove(observer);
         } else {
-            adapter.registerDataSetObserver(observer);
+            adapter.unregisterDataSetObserver(observer);
         }
     }
 

commons/src/main/java/org/wikimedia/commons/media/MediaDetailFragment.java

@@ -278,6 +278,10 @@ public void onDestroyView() {
             getView().getViewTreeObserver().removeOnScrollChangedListener(scrollListener);
             scrollListener  = null;
         }
+        if (dataObserver != null) {
+            detailProvider.unregisterDataSetObserver(dataObserver);
+            dataObserver = null;
+        }
         super.onDestroyView();
     }