Question

I’ve tried to implement the Google Map View tutorial on the Android developer site, but I keep running into a problem when trying to display an AlertDialog when I click on the overlay image. The problem is that mContext is null when calling

AlertDialog.Builder dialog = new AlertDialog.Builder(mContext);

in HelloItemizedOverlay’s onTap method because the constructor

public HelloItemizedOverlay(Drawable defaultMarker, Context context) {
    super(boundCenterBottom(defaultMarker));
    mContext = context;
}

is never called (that I can tell) which initializes mContext. When I replace

HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(drawable);

with

HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(drawable, 
                this.getApplicationContext());

in HelloGoogleMaps’s onCreate method in order to initialize the context, I get an exception

android.view.WindowManager$BadTokenException: Unable to add window — token null is not for an application

when I try to display the AlertDialog like so:

dialog.show();

I assume this tutorial has been successfully implemented by thousands of people, so I’m at a loss why no one else has run into this problem… have I missed an important step from the tutorial?

Answer 1

I think you need to pass mapView’s context to the HelloItemizedOverlay constructor like so:

HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(drawable, mapView.getContext());

There is clearly an error in the tutorial’s code sample. Small errors and omissions like this are not uncommon within reference documentation, especially for a large project like Android.