Question

I’m trying to follow the overlay instructions provided here:
https://developer.apple.com/library/ios/#documentation/UserExperience/Conceptual/LocationAwarenessPG/AnnotatingMaps/AnnotatingMaps.html#//apple_ref/doc/uid/TP40009497-CH6-SW15+

but the overlay isn’t showing. Here’s a step by step of what I’ve done so far:

1.) Added a new View Controller object to the storyboard
2.) Added a Map View object to the new view controller
3.) Went to File, New, New File…, UIViewController subclass, named it “MapViewController”, which added three files to my project: MapViewController.h, MapViewController.m, and MapViewController.xib
4.) Then I went to the view controller and defined its class as MapViewController
5.) Then “Control” + Clicked the MKMapView object over to the MapViewController.h which created: “@property (weak, non atomic) IBOutlet MKMapView *MKPolygonView;
6.) I then added the appropriate code to my .h and .m files to reflect the example, which I’ll include a copy of below

When I start the iOS simulator the map shows up, but the overlay doesn’t. What am I doing wrong?

MapViewController.h :

//
//  MapViewController.h
//  GeoShapes
//
//  Created by Template User on 4/1/12.
//  Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//

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

@interface MapViewController : UIViewController <MKMapViewDelegate> {

    IBOutlet MKMapView *map;

}

@property (weak, nonatomic) IBOutlet MKMapView *MKPolygonView;


@end

MapViewController.m :

//
//  MapViewController.m
//  GeoShapes
//
//  Created by Template User on 4/1/12.
//  Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//

#import "MapViewController.h"

@implementation MapViewController
@synthesize MKPolygonView;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
}
    return self;
}

- (void)didReceiveMemoryWarning
{
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];

    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
}

- (void)viewDidUnload
{
    [self setMKPolygonView:nil];
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;

    // 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";

    [map addOverlay:poly];
}

- (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;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

@end

Answer 1

Move the code bellow in viewDidUnload to viewDidLoad:

[self setMKPolygonView:nil];

// 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";

[map addOverlay:poly];