MapKit : add MKPolyline hide MKTileOverlay - objective-c

Question

I have a MKMapView working with a MKTileOverlay showing tiles from a local database. It's working fine.
Then I used MKDirections to get direction between two coordinates and draw the route like that :
MKRoute *route = response.routes.lastObject;
MKPolyline *polyline = route.polyline;
// Draw path on overlay
[self.mapView insertOverlay:polyline aboveOverlay:self.tileOverlay];
But when I zoom to see the line, it appears without the tile background (normaly loaded from MKTileOverlay (stored into self.tileOverlay)). I joined an image to see better.
I also made this code to render overlays :
- (MKOverlayRenderer *)mapView:(MKMapView *)mapView rendererForOverlay:(id<MKOverlay>)overlay {
if ([overlay isKindOfClass:[MKTileOverlay class]]) {
return [[MKTileOverlayRenderer alloc] initWithTileOverlay:overlay];
}
else if ([overlay isKindOfClass:[MKPolyline class]]) {
MKPolylineRenderer *lineView = [[MKPolylineRenderer alloc] initWithOverlay:overlay];
lineView.strokeColor = [UIColor greenColor];
lineView.lineWidth = 3;
return lineView;
}
return nil;
}
It's like the "tile" that render the line hide the tile loaded from the MKTileOverlay. How can I :
- specify that I the MKPolyline overlay must be transparent ?
- reload the background tile ?
Screeshot :
See the tile with line has no background anymore http://sigmanet.ch/tmp/screen.png

Answer 1

After days of work, here is my own solution.
Extend MKPolylineRenderer and add a reference to the MKTileOverlayRenderer. Let's call this new class MCPolylineRenderer.
In this class, override this two methods :
- (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context {
// Draw path only if tile render has a tile
if ([self.tileRenderRef canDrawMapRect:mapRect zoomScale:zoomScale]) {
[super drawMapRect:mapRect zoomScale:zoomScale inContext:context];
}
}
- (BOOL)canDrawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale {
// We can draw path only if tile render can also
return [self.tileRenderRef canDrawMapRect:mapRect zoomScale:zoomScale];
}
Now, in the mapView:renderedForOverlay method, replace
MKPolylineRenderer *lineView = [[MKPolylineRenderer alloc] initWithOverlay:overlay];
with
MCPolylineRenderer *lineView = [[MCPolylineRenderer alloc] initWithPolyline:overlay];
lineView.tileRenderRef = self.tileRender;
Also, you need to be sure that the loadTileAtPath:result: method doesn't result a tile when there is nothing to render (like a "tile not found" image).
This code will have effect that when there is no background tile to render, the path won't be draw neither.

Answer 2

You'll have to subclass MKPolylineRenderer to synchronize renderers drawing abilities.
import Foundation
import MapKit
class MyPolylineRenderer: MKPolylineRenderer {
var tileRenderer: MKTileOverlayRenderer?
override func draw(_ mapRect: MKMapRect, zoomScale: MKZoomScale, in context: CGContext) {
if (tileRenderer?.canDraw(mapRect, zoomScale: zoomScale) ?? true) {
super.draw(mapRect, zoomScale: zoomScale, in: context)
}
}
override func canDraw(_ mapRect: MKMapRect, zoomScale: MKZoomScale) -> Bool {
return tileRenderer?.canDraw(mapRect, zoomScale: zoomScale) ?? super.canDraw(mapRect, zoomScale: zoomScale)
}
}
Then in your MKMapViewDelegate, keep a reference to your tileRenderer and implement the rendererForOverlay :
var tileRenderer: MKTileOverlayRenderer?
public func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
if let polyline = overlay as? MKPolyline {
let lineRenderer = NXPolylineRenderer(overlay: overlay)
lineRenderer.tileRenderer = tileRenderer
// Configure your polyline overlay renderer here...
return lineRenderer;
}
if let tileOverlay = overlay as? MKTileOverlay {
if tileRenderer == nil || tileRenderer.overlay != overlay {
tileRenderer = MKTileOverlayRenderer(overlay: overlay)
}
return tileRenderer
}
return MKOverlayRenderer(overlay: overlay)
}
All credits for the idea goes to #Jonathan, I'm just posting a swift ready to copy/paste code for newcomers.