Xcode and iOS: debugQuickLookObject() showing MKMapView - ios

Question

In Xcode if you hover over a variable of type CLLocation and klick on the eye symbol, Xcode shows that location on a map.
To find bugs in data that is not mine, I wanted to have the same behaviour for objects of type MKPolyline.
First the test code:
import XCTest
import MapKit
class PolylineQuicklookTests: XCTestCase {
func testPolylineQuicklook() throws {
let wilhelma = CLLocationCoordinate2D(latitude: 48.804513, longitude: 9.206237)
let fernsehturm = CLLocationCoordinate2D(latitude: 48.755890, longitude: 9.190290)
let path = [wilhelma, fernsehturm]
let polyline = MKPolyline(coordinates: path, count: path.count)
print("set breakpoint here and test polyline Quicklook")
}
}
extend MKPolyline to invoke Quicklook:
extension MKPolyline {
#objc public func debugQuickLookObject() -> Any? {
//return "MKPolyline \(self.coordinates.count)"
quickLookMapVC = QuickLookMapVC(overlays: [self], annotations: [])
let view = quickLookMapVC?.view
return view
}
}
// hold reference:
fileprivate var quickLookMapVC: QuickLookMapVC?
And a simple implementation:
fileprivate class QuickLookMapVC: UIViewController {
var overlays: [MKOverlay] = []
var annotations: [MKAnnotation] = []
var mapView = MKMapView(frame: CGRect(x: 0, y: 0, width: 400, height: 400))
var testLabel = UILabel()
init() {
super.init(nibName: nil, bundle: nil)
}
convenience init(overlays: [MKOverlay], annotations: [MKAnnotation]) {
self.init()
print("QuickLookMapVC init \(overlays.count), \(annotations.count)")
self.overlays = overlays
self.annotations = annotations
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
// MARK: - View lifecycle
override func viewDidLoad() {
super.viewDidLoad()
print("QuickLookMapVC start viewDidLoad")
/*
testLabel.text = "Test"
testLabel.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(self.testLabel)
let constraints = [
testLabel.topAnchor.constraint(equalTo: view.topAnchor),
testLabel.leftAnchor.constraint(equalTo: view.leftAnchor),
view.bottomAnchor.constraint(equalTo: testLabel.bottomAnchor),
view.rightAnchor.constraint(equalTo: testLabel.rightAnchor)
]
NSLayoutConstraint.activate(constraints)
*/
mapView.delegate = self
mapView.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(self.mapView)
let constraints = [
mapView.topAnchor.constraint(equalTo: view.topAnchor),
mapView.leftAnchor.constraint(equalTo: view.leftAnchor),
view.bottomAnchor.constraint(equalTo: mapView.bottomAnchor),
view.rightAnchor.constraint(equalTo: mapView.rightAnchor)
]
NSLayoutConstraint.activate(constraints)
mapView.mapType = .standard
mapView.addOverlays(overlays)
mapView.addAnnotations(annotations)
let stuttgart = MKCoordinateRegion(center: CLLocationCoordinate2D(latitude: 48.775846, longitude: 9.182932),
latitudinalMeters: 5000, longitudinalMeters: 5000)
mapView.region = stuttgart
/*
if annotations.count > 0 {
mapView.showAnnotations(annotations, animated: true)
}
if let firstOverlay = overlays.first {
let mapRect = firstOverlay.boundingMapRect
print(mapRect)
mapView.visibleMapRect = mapRect
}
*/
}
}
extension QuickLookMapVC: MKMapViewDelegate {
func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
if let polyline = overlay as? MKPolyline {
print("rendererFor polyline")
// for real applications do reuse instead of creating a new one each time:
let polylineRenderer = MKPolylineRenderer(polyline: polyline)
polylineRenderer.strokeColor = .red
// lineWith: defaults to 0, which is MKRoadWidthAtZoomScale(currentZoomScale)
return polylineRenderer
}
if let polygon = overlay as? MKPolygon {
print("rendererFor polygon")
let polygonrenderer = MKPolygonRenderer(polygon: polygon)
polygonrenderer.fillColor = .red
return polygonrenderer
}
print("rendererFor overlay")
return MKOverlayRenderer(overlay: overlay)
}
}
I'd expect so see at least a map.
What I'm seeing is an MKMapView with the usual Apple copyright symbols but no map.
The copyright symbols let me assume that the mapView is at least sized correctly and rendered.
Console shows
QuickLookMapVC init 1, 0
QuickLookMapVC start viewDidLoad
rendererFor polyline
When I replace MKMapView with a UILabel, the label is shown correctly.
This lets me assume that the invocation and the UIViewController parts work fine and only MKMapView is a problem.
What can I do that my code actually shows map data and a polyline?