To add an annotation and respond to touching a button within the annotation:

1. Start with an existing MKMapView or review the Displaying a Location and Add an Annotation Recipes.

2. Add an annotation as you normally would:

   var annotation = new BasicMapAnnotation
   	(new CLLocationCoordinate2D (48.857, 2.351), "Paris", "City of Light");
   mapView.AddAnnotation (annotation);
   

3. Create a MKMapViewDelegate subclass (as shown). Notice how the GetViewForAnnotation method adds features such as the LeftCalloutAccessoryView and RightCalloutAccessoryView.

    protected class MapDelegate : MKMapViewDelegate
    {
    	protected string annotationIdentifier = "BasicAnnotation";
    	UIButton detailButton;
    	MapViewController parent;
    	public MapDelegate(MapViewController parent)
    	{
    		this.parent = parent;
    	}
    	/// <summary>
    	/// This is very much like the GetCell method on the table delegate
    	/// </summary>
    	public override MKAnnotationView GetViewForAnnotation (MKMapView mapView, IMKAnnotation annotation)
    	{
    		// try and dequeue the annotation view
    		MKAnnotationView annotationView = mapView.DequeueReusableAnnotation(annotationIdentifier);
    		// if we couldn't dequeue one, create a new one
    		if (annotationView == null)
    			annotationView = new MKPinAnnotationView(annotation, annotationIdentifier);
    		else // if we did dequeue one for reuse, assign the annotation to it
    			annotationView.Annotation = annotation;
    		// configure our annotation view properties
    		annotationView.CanShowCallout = true;
    		(annotationView as MKPinAnnotationView).AnimatesDrop = true;
    		(annotationView as MKPinAnnotationView).PinColor = MKPinAnnotationColor.Green;
    		annotationView.Selected = true;
    		// you can add an accessory view, in this case, we'll add a button on the right, and an image on the left
    		detailButton = UIButton.FromType(UIButtonType.DetailDisclosure);
    		detailButton.TouchUpInside += (s, e) => {
    			Console.WriteLine ("Clicked");
    			//Create Alert
    			var detailAlert = UIAlertController.Create ("Annotation Clicked", "You clicked on " +
    				(annotation as MKAnnotation).Coordinate.Latitude.ToString() + ", " +
    				(annotation as MKAnnotation).Coordinate.Longitude.ToString(), UIAlertControllerStyle.Alert);
    			detailAlert.AddAction (UIAlertAction.Create ("OK", UIAlertActionStyle.Default, null));
    			parent.PresentViewController (detailAlert, true, null);
    		};
    		annotationView.RightCalloutAccessoryView = detailButton;
    		annotationView.LeftCalloutAccessoryView = new UIImageView(UIImage.FromBundle("29_icon.png"));
    		return annotationView;
    	}
   
    	// as an optimization, you should override this method to add or remove annotations as the
    	// map zooms in or out.
    	public override void RegionChanged (MKMapView mapView, bool animated) {}
    }
   

4. Finally, assign the delegate (prior to the code added earlier to add the annotation to the MKMapView instance):

    // assign the delegate, which handles annotation layout and clicking
    // the Delegate needs to be assigned before adding the annotation
    mapView.Delegate = new MapDelegate(this);
   
    var annotation = new BasicMapAnnotation
    	(new CLLocationCoordinate2D (48.857, 2.351), "Paris", "City of Light");
    mapView.AddAnnotation (annotation);