MKAnnotationView not showing image on mapview in iOS

Question

I am getting some image url from web server, which I need to display on mapview. I have added function for MKAnnotationView and parsed the url, however its not showing on map view. Below is my code. Please let me know, if I am doing anything wrong.

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation
{
    static NSString *identifier = @"CustomAnnotation";
    MKAnnotationView* annView = nil;
    if ([annotation isKindOfClass:[MapViewAnnotation class]]) {

        annView = (MKAnnotationView *) [mapView dequeueReusableAnnotationViewWithIdentifier:identifier];
        if (annView == nil) {
            annView = [[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:identifier];
        } else {
            annView.annotation = annotation;
        }

        for(int i=0;i<array.count;i++) {

            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

                NSURL *iconurl = [NSURL URLWithString:[[array objectAtIndex:i]valueForKey:@"icon"]];
                UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:iconurl]];

                dispatch_async(dispatch_get_main_queue(), ^ {

                    UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
                    [annView addSubview:imageView];
                    [annView setFrame:CGRectMake(0, 0, imageView.frame.size.width, imageView.frame.size.height)];
                });
            });
        }

        UIButton*accessory = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
        [accessory addTarget:self action:@selector(openDetail:) forControlEvents:UIControlEventTouchUpInside];
        [accessory setFrame:CGRectMake(0, 0, 30, 30)];
        [annView setRightCalloutAccessoryView:accessory];
    }
    [annView setEnabled:YES];
    [annView setCanShowCallout:YES];
    return annView;
}

This code, which iterates through an array of image URLs, all presumably overlapping, is very curious. Why are you doing that? If you're trying to animate, this is not the way to do this. — Rob
– Rob, Commented Sep 18, 2016 at 16:39
While I disagree with Matt's contention that you cannot update the annotation view asynchronously (because you can), in practice, I'd go with him insofar that it's probably not recommended. If you have a standard annotation view image, download that in advance. I just think it's going to be a frustrating UX if someone taps on the button and nothing happens for a few seconds while the image is retrieved. — Rob
– Rob, Commented Sep 18, 2016 at 16:43

Rob · Accepted Answer · 2016-09-18 16:37:46Z

1

First, make sure you've specified the delegate of the map view and confirm that your viewForAnnotation is getting called at all.

Second, you're adding the UIImageView as a subview of the MKAnnotationView. Generally you just set the image property of the MKAnnotationView itself.

answered Sep 18, 2016 at 16:37

Rob

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