title: Show callout when tapping overlay
body: <p>I have an MKMapView with several overlays. Works all just fine, and it's incredible how simple it works. There is, however, one thing I can't get to work. The idea is simple: when a user taps within the area that is covered by an overlay, a callout with some information about that overlay has to come up. The overlays are all <code>MKPolygon</code>s, which follow the MKOverlay protocol and therefore the MKAnnotation protocol.</p>
  
  <blockquote>
    <p>The MKOverlay protocol conforms to the
    MKAnnotation protocol. As a result,
    all overlay objects are also
    annotation objects and     can be
    treated as one or both in your code.
    If you opt to treat an overlay object
    as both, you are responsible for
    managing that object in two places. If
    you want to display both an overlay
    view and annotation view for it, you
    must implement both the
    mapView:viewForOverlay: and
    mapView:viewForAnnotation: methods in
    your application delegate. It also
    means that you must add and remove the
    object from both the overlays and
    annotations arrays of your map.</p>
  </blockquote>
  
  <p>This comes from the Apple docs. I tried something like this:</p>
  
  <pre><code>- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id &lt;MKAnnotation&gt;)annotation {
  
        MKAnnotationView *aView = [[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:nil];
        aView.canShowCallout = YES;
  }
  </code></pre>
  
  <p>But that doesn't seem to work. I've tried using gesture recognizers, but I have no idea how to show a callout other than by using the <code>canShowCallOut</code> property...</p>