iOS 11 doesn't grab screen from MKMapView - swift

Question

I have an app that displays the locations the user has walked on an MKMapView. When the user leaves the map view the app grabs the screen and saves the image on disk. Up til iOSS 10.3 this method was always successful. With iOS 11.0 the screen grab is a blank image. I get no notification from xcode that there were some changes and that I need to adjust the code.
Interestingly, screen grabs from text pages are still grabbed and saved successfully.
Did anyone encounter the same problem and got the solution?
The code that has always been successful up til now, is:
override func viewWillDisappear(_ animated: Bool) {
//Set the full file name under which the track will be saved.
let fileBaseName = self.imageName.appending(String(describing: (self.display?.trackDate)!))
let fileFullName = fileBaseName.appending(".png")
//Check if the image already has been saved
if !AuxiliaryObjects.shared.getImageFileName(with: fileFullName ) {
//Create the sizes of the capture
let screenRect = self.trackMapView.frame
let screenSize = screenRect.size
let screenScale = UIScreen.main.scale
var grabRect = self.trackMapView.convertRegion(self.mapRegion, toRectTo: self.view)
var heightAdjustment : CGFloat = 0.0
//Grab the image from the screen
UIGraphicsBeginImageContextWithOptions(screenSize, false, screenScale)
self.trackMapView.drawHierarchy(in: screenRect, afterScreenUpdates: true)
let myImage = UIGraphicsGetImageFromCurrentImageContext()
grabRect.origin.x *= (myImage?.scale)!
grabRect.origin.y *= (myImage?.scale)!
grabRect.size.width *= (myImage?.scale)!
grabRect.size.height *= (myImage?.scale)!
let grabImage = (myImage?.cgImage)!.cropping(to: grabRect)
let mapImage = UIImage(cgImage: grabImage!)
UIGraphicsEndImageContext()
AuxiliaryObjects.shared.save(image: mapImage, with: fileFullName, and: self.imageName)
self.display?.displayImage = AuxiliaryObjects.shared.getImage(with: fileFullName, with: self.tableImageRect)!
} else {
self.display?.displayImage = AuxiliaryObjects.shared.getImage(with: fileFullName, with: self.tableImageRect)!
}
}

Answer 1

I submitted a code level support request at Apple to get the answer to the question. Apple does not support the use of drawHierarhy in grabbing a MapKit screen. The way to go is using the MKMapSnapshotter utility to create an MKMapSnapshot and then draw in the lines and annotations by converting all the map coordinates to view coordinates.
Since this gave me some problems with getting the a mirrored image and translating the coordinates properly, I decided to use the layer method render(in: CGContext) this provided me a well functioning very efficient screen grab.
func creatSnapshot(with fileName: String) {
UIGraphicsBeginImageContextWithOptions(self.trackMapView.frame.size, false, UIScreen.main.scale)
let currentContext = UIGraphicsGetCurrentContext()
self.trackMapView.layer.render(in: currentContext!)
let contextImage = (UIGraphicsGetImageFromCurrentImageContext())!
UIGraphicsEndImageContext()
let region = self.trackMapView.region
var cropRect = self.trackMapView.convertRegion(region, toRectTo: self.trackMapView.superview)
cropRect.origin.x *= contextImage.scale
cropRect.origin.y *= contextImage.scale
cropRect.size.height *= contextImage.scale
cropRect.size.width *= contextImage.scale
let cgMapImage = contextImage.cgImage?.cropping(to: cropRect)
let mapImage = UIImage(cgImage: cgMapImage!)
AuxiliaryObjects.shared.save(image: mapImage, with: fileName, and: self.imageName)
self.displayTrack?.displayImage = AuxiliaryObjects.shared.getImage(with: fileName, with: self.tableImageRect)!
NotificationCenter.default.post(name: self.imageSavedNotification, object: self)
}