android - Crash in ListView at AbsListView.obtainView for ListActivity

Question

I'm watching content updates on a ListActivity using a ContentObserver as follows:

protected void onCreate(Bundle savedState)
   {
        super.onCreate(savedState);

        ContentResolver cr = getContentResolver();

        Cursor cursor = cr.query(TrackHeader.CONTENT_URI, sTrackListProjection, null, null, null);
        startManagingCursor(cursor);

        this.mAdapter = new TrackHeaderDataAdapter(this, R.layout.track_list_item, cursor, sTrackListProjection, null);
        setListAdapter(mAdapter);

        Handler handler = new Handler();

        mTrackHeaderObserver = new ContentObserver(handler) {

             @Override 
             public boolean deliverSelfNotifications() { 
                 return false;
             }

             @Override
             public void onChange(boolean selfChange) {
                 super.onChange(selfChange);
                 ContentResolver cr = getContentResolver();
                 mAdapter.changeCursor(cr.query(TrackHeader.CONTENT_URI, sTrackListProjection, null, null, null));
              }
         };

      getContentResolver().registerContentObserver (TrackHeader.CONTENT_URI, true, mTrackHeaderObserver);
  }

This content observer seems to be ok -- it gets called back on the UI thread but I am getting the following random crash pretty predictably on the underlying ListView:

02-21 14:06:00.440: ERROR/AndroidRuntime(739): java.lang.NullPointerException
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at  android.widget.AbsListView.obtainView(AbsListView.java:1276)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.ListView.makeAndAddView(ListView.java:1668)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.ListView.fillDown(ListView.java:637)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.ListView.fillSpecific(ListView.java:1224)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.ListView.layoutChildren(ListView.java:1499)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.AbsListView.onLayout(AbsListView.java:1113)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.view.View.layout(View.java:6830)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.FrameLayout.onLayout(FrameLayout.java:333)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.view.View.layout(View.java:6830)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.FrameLayout.onLayout(FrameLayout.java:333)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.view.View.layout(View.java:6830)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.FrameLayout.onLayout(FrameLayout.java:333)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.view.View.layout(View.java:6830)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1119)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.LinearLayout.layoutVertical(LinearLayout.java:998)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.LinearLayout.onLayout(LinearLayout.java:918)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.view.View.layout(View.java:6830)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.FrameLayout.onLayout(FrameLayout.java:333)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.view.View.layout(View.java:6830)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.FrameLayout.onLayout(FrameLayout.java:333)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.view.View.layout(View.java:6830)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.widget.FrameLayout.onLayout(FrameLayout.java:333)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.view.View.layout(View.java:6830)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.view.ViewRoot.performTraversals(ViewRoot.java:996)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1633)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.os.Handler.dispatchMessage(Handler.java:99)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.os.Looper.loop(Looper.java:123)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at android.app.ActivityThread.main(ActivityThread.java:4363)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at java.lang.reflect.Method.invokeNative(Native Method)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at java.lang.reflect.Method.invoke(Method.java:521)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
02-21 14:06:00.440: ERROR/AndroidRuntime(739):     at dalvik.system.NativeStart.main(Native Method)
02-21 14:09:56.159: ERROR/AndroidRuntime(749): ERROR: thread attach failed
02-21 14:09:59.480: ERROR/AndroidRuntime(760): ERROR: thread attach failed
02-21 14:12:19.449: ERROR/AndroidRuntime(778): ERROR: thread attach failed
02-21 14:12:22.779: ERROR/AndroidRuntime(789): ERROR: thread attach failed
02-21 14:12:26.479: ERROR/gralloc(51): [unregister] handle 0x3f13b8 still locked (state=40000001)

Anyone seen anything like this before -- been stumped on this one for a few days...

Tim

Answer 1

I had a similar stack trace and discovered that I was returning a null from my getView() method in certain cases.