Swift 3 Add custom annotation pin to MKMapSnapShot

Question

I'm learning Swift 3 on my own, and my current learning project involves allowing the user to snap a photo and get a map snapshot with the current location pinned.

I've relied on this answer from Aug 2015 and this answer from Jun 2016 for guidance, but I still can't find the right path.

Right now, I can...

1. Get the photo from the buffer
2. Get a map snapshot

But I just can't place the pin. I know that my code is incomplete and ineffective -- so this is more than just a debugging question. Here is what I've been working with (as well as many variations based on the links above):

let snapShotter = MKMapSnapshotter(options: mapSnapshotOptions)

snapShotter.start() {

    snapshot, error in

        guard let snapshot = snapshot else {
            return
        }

        let image = snapshot.image
        let annotation = MKPointAnnotation()
        annotation.coordinate = needleLocation  // is a CLLocationCoordinate2D
        annotation.title = "My Title"

        let annotationView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: "annotation")

        // I want to push the final image to a global variable
        // can't figure out how to define finalImage as the pinned map
        self.myMap = finalImage


        } // close snapShotter.start

I've been stuck for days now, so I certainly would appreciate any insights. Thanks!

Answer 1

To render a MKMapSnapshot with annotation views, you have to manually draw the snapshot's image and the annotation view's image on a new graphic context, and get a new image from that context. In Swift 3:

let rect = self.imageView.bounds

let snapshot = MKMapSnapshotter(options: options)
snapshot.start { snapshot, error in
    guard let snapshot = snapshot, error == nil else {
        print("\(error)")
        return
    }

    UIGraphicsBeginImageContextWithOptions(options.size, true, 0)
    snapshot.image.draw(at: .zero)

    let pinView = MKPinAnnotationView(annotation: nil, reuseIdentifier: nil)
    let pinImage = pinView.image

    var point = snapshot.point(for: location.coordinate)

    if rect.contains(point) {
        let pinCenterOffset = pinView.centerOffset
        point.x -= pinView.bounds.size.width / 2
        point.y -= pinView.bounds.size.height / 2
        point.x += pinCenterOffset.x
        point.y += pinCenterOffset.y
        pinImage?.draw(at: point)
    }

    let image = UIGraphicsGetImageFromCurrentImageContext()

    UIGraphicsEndImageContext()

    // do whatever you want with this image, e.g.

    DispatchQueue.main.async {
        self.imageView.image = image
    }
}

This was adapted from https://stackoverflow.com/a/18776723/1271826, which itself was adapted from WWDC 2013 video Putting MapKit in Perspective.

Here is an example of a snapshot with a .satelliteFlyover:

Answer 2

I was getting an error from Rob's code that defines "rect" because my MKMapSnapshotter image is a UIImage. However .bounds is a property of UIImageView and not UIImage. So the rect definition throws an error.

Here is how I configured the options:

        let mapSnapshotOptions = MKMapSnapshotOptions()

        // Set the region of the map that is rendered.
        let needleLocation = CLLocationCoordinate2DMake(location.coordinate.latitude, location.coordinate.longitude)
        let region = MKCoordinateRegionMakeWithDistance(needleLocation, 1000, 1000)
        mapSnapshotOptions.region = region

        // Set the scale of the image. We'll just use the scale of the current device, which is 2x scale on Retina screens.
        mapSnapshotOptions.scale = UIScreen.main.scale

        // Set the size of the image output.
        mapSnapshotOptions.size = CGSize(width: 300, height: 300)

        // Show buildings and Points of Interest on the snapshot
        mapSnapshotOptions.showsBuildings = true
        mapSnapshotOptions.showsPointsOfInterest = false

So is there another way to access the .bounds property? Or have I created my snapshot incorrectly?