Android – ItemizedOverlay + ArrayIndexOutOfBoundsException / NullPointerException workarounds

There’s some gotchas to be aware of when using the ItemizedOverlay class Google provides.

Here’s the situation (a fairly common one): You have a dynamic list of Icons you wish to display on a map.  The list can grow and shrink.  You might think the following would work:

public class CustomItemizedOverlay extends ItemizedOverlay {

	private ArrayList mOverlays = new ArrayList();

	public CustomItemizedOverlay(Drawable defaultMarker, Context mContext, MapView view) {
		super(boundCenterBottom(defaultMarker));
	}

	@Override
	protected COINOverlayItem createItem(int i) {
		return mOverlays.get(i);
	}


	@Override
	public int size() {
		return mOverlays.size();
	}

	public void addOverlay(COINOverlayItem overlay) {
		mOverlays.add(overlay);
		populate();
	}


	public void clear() {
		mOverlays.clear();
		populate();
	}
}

Seems like a reasonable assumption, doesn’t it?  If you try to use this class, you will immediately see a problem – if you do not add any items to the list before it is displayed, you will get a NullPointerException.  This is well documented in two separate threads; Google has marked the issue as Won’tFix.  The workaround is to call populate() within the constructor.  OK, that’s fine.  Our new constructor looks like this:

public CustomItemizedOverlay(Drawable defaultMarker, Context mContext, MapView view) {
		super(boundCenterBottom(defaultMarker));

	        // Workaround for null pointer exception with empty list
		// <a href="http://osdir.com/ml/AndroidDevelopers/2009-08/msg01605.html">http://osdir.com/ml/AndroidDevelopers/2009-08/msg01605.html</a>
		// <a href="http://code.google.com/p/android/issues/detail?id=2035">http://code.google.com/p/android/issues/detail?id=2035</a>
		populate();
	}

You’re not out of the woods yet, though. Say you have clicked on one of the icons on the map. Now say you somehow change your list of icons, e.g. by clearing all of them off the map. Click on the same point where the icon USED to be, and you’ll be faced with a nasty stack trace:

10-19 11:02:48.009: ERROR/AndroidRuntime(1375): java.lang.ArrayIndexOutOfBoundsException
10-19 11:02:48.009: ERROR/AndroidRuntime(1375):     at com.google.android.maps.ItemizedOverlay.maskHelper(ItemizedOverlay.java:562)
10-19 11:02:48.009: ERROR/AndroidRuntime(1375):     at com.google.android.maps.ItemizedOverlay.setFocus(ItemizedOverlay.java:365)
10-19 11:02:48.009: ERROR/AndroidRuntime(1375):     at com.google.android.maps.ItemizedOverlay.focus(ItemizedOverlay.java:539)
10-19 11:02:48.009: ERROR/AndroidRuntime(1375):     at com.google.android.maps.ItemizedOverlay.onTap(ItemizedOverlay.java:455)
10-19 11:02:48.009: ERROR/AndroidRuntime(1375):     at org.mitre.coin.map.COINItemizedOverlay.onTap(COINItemizedOverlay.java:63)
10-19 11:02:48.009: ERROR/AndroidRuntime(1375):     at com.google.android.maps.OverlayBundle.onTap(OverlayBundle.java:83)
10-19 11:02:48.009: ERROR/AndroidRuntime(1375):     at com.google.android.maps.MapView$1.onSingleTapUp(MapView.java:346)
10-19 11:02:48.009: ERROR/AndroidRuntime(1375):     at android.view.GestureDetector.onTouchEvent(GestureDetector.java:503)
10-19 11:02:48.009: ERROR/AndroidRuntime(1375):     at com.google.android.maps.MapView.onTouchEvent(MapView.java:623)
10-19 11:02:48.009: ERROR/AndroidRuntime(1375):     at org.mitre.coin.view.ModifiedMapView.onTouchEvent(ModifiedMapView.java:26)
10-19 11:02:48.009: ERROR/AndroidRuntime(1375):     at android.view.View.dispatchTouchEvent(View.java:3368)

The source is closed, so you have no idea what is throwing the ArrayIndexOutOfBounds; it’s in code you didn’t write. Once again, there’s a workaround for it, but it’s certainly not intuitive, nor is it mentioned in the documentation. You must called setLastFocusedIndex(-1); whenever you structurally modify the list, but before you call populate(). The issue is documented in more detail here.

The skeleton now looks like the following:

public class CustomItemizedOverlay extends ItemizedOverlay {

	private ArrayList mOverlays = new ArrayList();

	public CustomItemizedOverlay(Drawable defaultMarker, Context mContext, MapView view) {
		super(boundCenterBottom(defaultMarker));

		// Workaround for bug that Google refuses to fix:
		// <a href="http://osdir.com/ml/AndroidDevelopers/2009-08/msg01605.html">http://osdir.com/ml/AndroidDevelopers/2009-08/msg01605.html</a>
		// <a href="http://code.google.com/p/android/issues/detail?id=2035">http://code.google.com/p/android/issues/detail?id=2035</a>
		populate();
	}

	@Override
	protected COINOverlayItem createItem(int i) {
		return mOverlays.get(i);
	}


	@Override
	public int size() {
		return mOverlays.size();
	}

	public void addOverlay(COINOverlayItem overlay) {
		mOverlays.add(overlay);
		setLastFocusedIndex(-1);
		populate();
	}


	public void clear() {
		mOverlays.clear();
		mapView.removeAllViews();
		numItems = 0;
		// Workaround for another issue with this class:
		// <a href="http://groups.google.com/group/android-developers/browse_thread/thread/38b11314e34714c3">http://groups.google.com/group/android-developers/browse_thread/thread/38b11314e34714c3</a>
		setLastFocusedIndex(-1);
		populate();
	}
}

Hopefully this pops up in Google and saves some people some trouble.