MKPolyline replacement causes MKTileOverlay to flash on map since iOS 13

Question

I have an MKMapView that has a MKTileOverlay so that I can show Open Street Map tiles:

NSString *templateURL = @"http://tile.openstreetmap.org/{z}/{x}/{y}.png";
self.tileOverlay = [[MKTileOverlay alloc] initWithURLTemplate:templateURL];
self.tileOverlay.canReplaceMapContent = YES;
[self.mapView addOverlay:self.tileOverlay level:MKOverlayLevelAboveLabels];

I also want to show an MKPolyline from my current location to Apple Park in Cupertino. This polyline needs to be updated as I move, and since an MKPolyline object isn't mutable, I have to remove it and add it for each location update:

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray*)locations {

    self.currentLocation = userLocation;

    // Update polyline
    CLLocationCoordinate2D applePark = CLLocationCoordinate2DMake(37.334626, -122.008895);
    [self buildPolylineWithDestinationLocation:applePark];

}

- (void)buildPolylineWithDestinationLocation:(CLLocationCoordinate2D)coordinate {

    // Remove the polyline each time so we can redraw it
    if (self.polylineApple) {
        [self.mapView removeOverlay:self.polylineApple];
    }

    // Get current location
    CLLocation *location = self.currentLocation;
    CLLocationCoordinate2D currentLocation = location.coordinate;
    CLLocationCoordinate2D points[2];
    points[0] = currentLocation;
    points[1] = coordinate;

    // Remove all route polylines
    MKPolyline *oldPolyline = self.polylineApple;

    // Draw a line
    self.polylineApple = [MKPolyline polylineWithCoordinates:points count:2];

    [self.mapView addOverlay:self.polylineApple];
    if (oldPolyline) {
        [self.mapView removeOverlay:oldPolyline];
        oldPolyline = nil;
    }

}

The problem is, this used to work great in older versions of iOS, but ever since iOS 13 this has caused the tiles to be redrawn each time that MKPolyline is removed and added:

Is this just an iOS 13 bug, or is there something I need to fix in my code to make this not happen?

Answer 1

As I know since iOS 8, I have seen this issue. Not always but some times.

This issue is linked to 2 things:

1) The action every second to remove and add again a polyline will ask the MKMapView to redrawn the part with the polyline and as a consequence the MKTileOverlay below.

2) If the tile's size (in KB, not the resolution) is low, the issue may not be present.

The best advice I can give to you is to add you own view to the MKMapView and update this own view by calling setNeedsDisplay. It will trigger the draw method where you can convert the map points (latitude, longitude) to screen points and draw the line.

Edit: A link speaking about MKTileOverlay reload issue

https://forums.developer.apple.com/message/313677#313677