Android : how to make the alertDialog options mutually-exclusive

I want to make a simple dialog alert with 3 options (800m, 1300m, 2000m), that are mutually exclusive. Below you can see how i created the AlertDialog using the Builder. I setted the default selected item to 0, and i would like to be able to change the selected item according to the "which" parameter of the clickListener. getSelectedItem position always returns -1 and setItemChecked doesn't seem to work either.

public static class ZoomTypes extends DialogFragment {
    @Override
    public Dialog onCreateDialog(final Bundle savedInstanceState) {
        final AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        builder.setTitle(R.string.menu_radius)
                .setSingleChoiceItems(R.array.menu_radius_array, 0, new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {

                        ((AlertDialog) dialog).getListView().getSelectedItemPosition(); // this is -1
                        ((AlertDialog) dialog).getListView().setItemChecked(which, true); //doesn't work
                        ((AlertDialog) dialog).hide();

                    }
                });
        return builder.create();
    }
}

and this are my menu items

 <string-array                     
          name="menu_radius_array"> 
      <item                         
              >800m                 
      </item>                       
      <item                         
              >1300m                
      </item>                       
      <item                         
              >2000m                
      </item>                       
  </string-array>   

Any ideea on how to update the checkedItem inside the onClickListener event ?