Objective-C MapKit Overlay on entire map

Question

How would I create an overlay that colors the entire map a certain color? Then I need to be able to place annotations on top of it. Any ideas? Thanks.

Answer 1

What you want is MKOverlay and MKOverlayView. You can find apple's code in one of the apps mentioned in 'Related sample code'. in above protocol and class reference page.

EDIT : As Per the comments previous code was not working as-is. Heres a MKMapDimOverlay GitHub project which you can simply integrate using CocoaPods. I have also made the relevant changes in following code in the answer.

To explain briefly, following is code for adding a dark overlay on entire map.

You need to create an overlay and add it to the map view.

MKMapDimOverlay *dimOverlay = [[MKMapDimOverlay alloc] initWithMapView:MapView];
[mapView addOverlay: dimOverlay];

Create and return MKOverlayView for the specific MKOverlay in 'viewForOverlay' delegate method

-(MKOverlayView *)mapView:(MKMapView *)mapView viewForOverlay:(id<MKOverlay>)overlay {
    if([overlay isMemberOfClass:[MKMapDimOverlay class]]) {
        MKMapDimOverlayView *dimOverlayView = [[MKMapDimOverlayView alloc] initWithOverlay:overlay];
        return dimOverlayView;
    }
}

Since all you want is a colored overlay covering the map, your overlay and overlay view implementation will be very simple.

DimOverlay.m

@interface DimOverlay ()
@property (nonatomic) CLLocationCoordinate2D dimOverlayCoordinates;
@end

@implementation DimOverlay

-(id)initWithMapView:(MKMapView *)mapView {
    self = [super init];
    if(self)
    {
        self.dimOverlayCoordinates = mapView.centerCoordinate;
    }
    return self;
}

-(CLLocationCoordinate2D)coordinate {
    return self.dimOverlayCoordinates;
}

-(MKMapRect)boundingMapRect {
    return MKMapRectWorld;
}

@end

DimOverlayView.m

@implementation DimOverlayView

- (void)drawMapRect:(MKMapRect)mapRect
          zoomScale:(MKZoomScale)zoomScale
          inContext:(CGContextRef)ctx {
    /*
     You can allow custom colors and opacity values.
     Simply add UIColor and CGFloat properties in the overlay view class 
     and use those properties instead of the default hardcodes values below.
    */
    CGContextSetAlpha(ctx, 0.85);
    CGContextSetFillColorWithColor(ctx, [UIColor blackColor].CGColor);
    CGContextFillRect(ctx, [self rectForMapRect:mapRect]);
}

@end