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How to add a button to an MKMapView annotation

Paul Hudson       @twostraws

The built-in MKPinAnnotationView annotation view has a rightCalloutAccessoryView property that can be set to any kind of UIView, including buttons. The button doesn't need to have an action attached to it, because there's a separate method that gets called when it's tapped.

First up, here's how you'd create a button inside an annotation view:

let btn = UIButton(type: .detailDisclosure)
annotationView.rightCalloutAccessoryView = btn

For context, here's a complete implementation of viewForAnnotation that uses a button. This is taken from project 19 of Hacking with Swift, where I created a class called Capital that implemented the MKAnnotation protocol – you'll need to adjust this for your own annotation type:

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
    let identifier = "Capital"

    if annotation is Capital {
        if let annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: identifier) {
            annotationView.annotation = annotation
            return annotationView
        } else {
            let annotationView = MKPinAnnotationView(annotation:annotation, reuseIdentifier:identifier)
            annotationView.isEnabled = true
            annotationView.canShowCallout = true

            let btn = UIButton(type: .detailDisclosure)
            annotationView.rightCalloutAccessoryView = btn
            return annotationView
        }
    }

    return nil
}

When it comes to detecting taps on your button, implement the calloutAccessoryControlTapped method. This tells you the annotation view that was tapped (from which you can pull out the annotation), the control that was tapped (in our case it's a button), and also the map view the whole thing belongs to. Here's an example:

func mapView(_ mapView: MKMapView, annotationView view: MKAnnotationView, calloutAccessoryControlTapped control: UIControl) {
    let capital = view.annotation as! Capital
    let placeName = capital.title
    let placeInfo = capital.info

    let ac = UIAlertController(title: placeName, message: placeInfo, preferredStyle: .alert)
    ac.addAction(UIAlertAction(title: "OK", style: .default))
    present(ac, animated: true)
}

Available from iOS 2.0 – see Hacking with Swift tutorial 19

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