Question

For an app I’m building, I have a custom “old map” effect PNG that I’d like to overlay on the MKMapView view. Unfortunately, neither way I’ve tried to do this is exactly right:

1. Add a subview to the MKMapView (issue: the UIImageView for the PNG gets placed above the Annotation pins, which looks weird
2. Make the image an annotation view itself and place it below the other ones (issue: on scroll, I have to move the annotation view image, and for a while there’s just the regular map instead of the old-timey-effect).

What I basically want to accomplish is having a subview that is layered above the maptiles but below the annotation views, and that will hold steady while the user scrolls around—any thoughts?

Answer 1

Note that all MKMapView subviews hierarchy, annotations, behaviour etc proceeds in internal private MKMapViewInternal class so changing anything (in a way I suggest or another) in this structure may cause your application to be rejected from Appstore.

I do not have a full solution, just an idea. My idea is to make an overlay view have the same superview as annotation views and ensure that annotations will be placed over our overlay. In MKMapViewDelegate we implement:

- (void)mapView:(MKMapView *)aMapView didAddAnnotationViews:(NSArray *)views{
    if (views.count > 0){
        UIView* tView = [views objectAtIndex:0];

        UIView* parView = [tView superview];
        UIView* overlay = [tView viewWithTag:2000];
        if (overlay == nil){
            overlay = [[UIImageView alloc] initWithImage:[UIImage imageNamed:MY_IMAGE_NAME]];
            overlay.frame = parView.frame; //frame equals to (0,0,16384,16384)
            overlay.tag = 2000;
            overlay.alpha = 0.7;
            [parView addSubview:overlay];
            [overlay release];
        }

        for (UIView* view in views)
            [parView bringSubviewToFront:view];
    }
}

This code does a half of what you want – you get a view placed between map tiles and annotations. The remaining task is to change custom overlay view frame according to map scrolling/zooming (I’ll post if I find the way).