MKPolygon using Swift (Missing argument for parameter 'interiorPolygons' in call) - ios7

Question

Fellow Devs,
I'm trying to implement a polygon overlay on a mapview as follows:
private func drawOverlayForObject(object: MyStruct) {
if let coordinates: [CLLocationCoordinate2D] = object.geometry?.coordinates {
let polygon = MKPolygon(coordinates: coordinates, count: coordinates.count)
self.mapView.addOverlay(polygon)
}
}
The following error is presented:
Missing argument for parameter 'interiorPolygons' in call
According to the documentation:
Apple Docu:
Mutable Pointers
When a function is declared as taking an UnsafeMutablePointer
argument, it can accept any of the following:
nil, which is passed as a null pointer
An UnsafeMutablePointer value
An in-out expression whose operand is a stored lvalue of type Type, which is passed as the address of the lvalue
An in-out [Type] value, which is passed as a pointer to the start of the array, and lifetime-extended for the duration of the call
Now I think that my approach then would be correct, providing a [CLLocationCoordinate2D] array. Did anyone experience the same problem and found a workaround?
thanks
Ronny

Answer 1

The error you're getting is Swift's cryptic way of saying that it can't find a method which matches your parameters. If you did try passing the interiorPolygons parameter, you'd get an equally confusing:
Extra argument 'interiorPolygons' in call
Your code is pretty close though; you just need a couple of minor changes. In the doc you reference, it says one of the things you can pass is:
An in-out [Type] value, which is passed as a pointer to the start of
the array, and lifetime-extended for the duration of the call
So, it's looking for an in-out parameter. Which is done by passing coordinates prefixed with an &, like so:
MKPolygon(coordinates: &coordinates, count: coordinates.count)
But, in-out parameters can't be constants. From the docs:
You can only pass a variable as the argument for an in-out parameter.
You cannot pass a constant or a literal value as the argument, because
constants and literals cannot be modified.
So, you need to define coordinates with a var first:
if var coordinates: [CLLocationCoordinate2D] = object.geometry?.coordinates
Which makes the entire function look like this:
private func drawOverlayForObject(object: MyStruct) {
if var coordinates: [CLLocationCoordinate2D] = object.geometry?.coordinates {
let polygon = MKPolygon(coordinates: &coordinates, count: coordinates.count)
self.mapView.addOverlay(polygon)
}
}

Answer 2

My final solution by cherry-picking from several tutorials and integrating:
func setPolylineFromPoints(locations:[CLLocation]){
if locations.count == 0 {
return;
}
// while we create the route points, we will also be calculating the bounding box of our route
// so we can easily zoom in on it.
var pt : UnsafeMutablePointer<MKMapPoint>? // Optional
pt = UnsafeMutablePointer.alloc(locations.count)
for idx in 0..<locations.count-1 {
let location = locations[idx]
let point = MKMapPointForCoordinate(location.coordinate);
pt![idx] = point;
}
self.polyline = MKPolyline(points:pt!, count:locations.count-1)
// clear the memory allocated earlier for the points
pt?.destroy()
pt?.dealloc(locations.count)
}