How to: Display MKOverlay on MKMapView

Question

I need to display an MKOverlay on a map, but can't get it to actually appear.

I'm following the example from Apple's Location Awareness Programming Guide and the overlay wont display. Any help would be greatly appreciated, this is the first iPhone app I've made, so I might be missing something simple.

NavViewController.h

#import <UIKit/UIKit.h>
#import <MapKit/MapKit.h>

@interface NavViewController : UIViewController <MKMapViewDelegate> {
}
@property (weak, nonatomic) IBOutlet MKMapView *mapView;

@end

NavViewController.m

#import "MSUNavViewController.h"
#import <CoreLocation/CoreLocation.h>

- (MKOverlayView *)mapView:(MKMapView *)mapView viewForOverlay:(id <MKOverlay>)overlay
{
    if ([overlay isKindOfClass:[MKPolygon class]])
    {
        MKPolygonView* aView = [[MKPolygonView alloc] initWithPolygon:(MKPolygon*)overlay];

        aView.fillColor = [[UIColor cyanColor] colorWithAlphaComponent:0.2];
        aView.strokeColor = [[UIColor blueColor] colorWithAlphaComponent:0.7];
        aView.lineWidth = 3;

        return aView;
    }
    return nil;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Define an overlay that covers Colorado.
    CLLocationCoordinate2D  points[4];

    points[0] = CLLocationCoordinate2DMake(41.000512, -109.050116);
    points[1] = CLLocationCoordinate2DMake(41.002371, -102.052066);
    points[2] = CLLocationCoordinate2DMake(36.993076, -102.041981);
    points[3] = CLLocationCoordinate2DMake(36.99892, -109.045267);

    MKPolygon* poly = [MKPolygon polygonWithCoordinates:points count:4];
    poly.title = @"Colorado";

    [_mapView addOverlay:poly];
}

Storyboard:

Any coding suggestions would be greatly appreciated. Thanks!

Answer 1

Make sure to set mapView's delegate to the view controller instance( perhaps File's owner in this case).

In interface builder, right-click on the map view, drag from hollowed circle at the right of delegate, to the File's Owner icon at the Placeholder section in the pane on the left.

For storyboard, connect to the View Controller icon instead of File's Owner.

Answer 2

Probably you killing aView in - (MKOverlayView *)mapView:(MKMapView *)mapView viewForOverlay:(id <MKOverlay>)overlay by return nil; Try to add else before.

- (MKOverlayView *)mapView:(MKMapView *)mapView viewForOverlay:(id <MKOverlay>)overlay
{
    if ([overlay isKindOfClass:[MKPolygon class]])
    {
        MKPolygonView* aView = [[MKPolygonView alloc] initWithPolygon:(MKPolygon*)overlay];

        aView.fillColor = [[UIColor cyanColor] colorWithAlphaComponent:0.2];
        aView.strokeColor = [[UIColor blueColor] colorWithAlphaComponent:0.7];
        aView.lineWidth = 3;

        return aView;
    }
    else return nil;
} 

Answer 3

Did you solve your problem? Just drag from the circle beside delegate (in your screen shot) to the circle which is the name of the class.. there is a setting in the inspector that would allow you to display where you are also..? You made need to centre the map in say viewDidLoad so it displays over Colorado..