Ios – mapView:viewForAnnotation: not called when delegate set in code

iosiphonemapkitmkannotationobjective c

I have a custom class for my MKAnnotations, I want to override the default mapView:viewForAnnotatation method so that I can add extra information in the callout. When I set my delegate in code (as per the code below) the annotations are dropped on the map and are selectable but my mapView:viewForAnnoation is never called.

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation{
    NSLog(@"viewForAnnotation: called");
    MKAnnotationView *aView = [mapView dequeueReusableAnnotationViewWithIdentifier:@"mapPin"];
    if(!aView){
        aView = [[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"mapPin"];
    }
    aView.annotation = annotation;

    return aView;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Do any additional setup after loading the view.
    self.mapView.delegate = self;

}

I know the delegate is being set as I can override the method -(void)mapView:(MKMapView *)mapView didSelectAnnotationView:(MKAnnotationView *)view and I see an NSLog when I select an annotation.

When I change from setting the delegate in code to setting it in the Storyboard the method is called (NSLog(@"viewForAnnotation: called"); statements appear) but the annotations don't appear on the map and sometimes this error appears:

<Error>: ImageIO: CGImageReadSessionGetCachedImageBlockData *** CGImageReadSessionGetCachedImageBlockData: bad readSession [0x8618480]

Best Answer

This seems like two separate issues:

Regarding the setting delegate in code v storyboard, it's hard to reconcile your various observations (delegate method didSelectAnnotationView is getting called in both scenarios, but viewForAnnotation is not). The only difference between setting it in code v in the storyboard is the timing of when the delegate is getting set. You're not showing us the process of adding the annotations, so it's hard to diagnose on the basis of what you've described. If none of your delegate methods were getting called, I'd suspect the mapView IBOutlet, but if some are working and others aren't, I can only suspect a timing issue.
Regarding the setting of the MKAnnotationView, the default implementation does nothing. You either need to write your own subclass of MKAnnotationView, set its image if you're using your own image, or, much easier, just use MKPinAnnotationView. But just creating a MKAnnotationView won't do anything. You really want:
```
- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation{
    // If it's the user location, just return nil.
    if ([annotation isKindOfClass:[MKUserLocation class]])
        return nil;

    // Handle any custom annotations.
    MKAnnotationView *aView = [mapView dequeueReusableAnnotationViewWithIdentifier:@"mapPin"];
    if(aView){
        aView.annotation = annotation;
    } else {
        aView = [[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"mapPin"];
    }

    aView.canShowCallout = NO;

    return aView;
}
```
(Note, I'm not only creating a MKPinAnnotationView, but I'm also making sure that it's not a MKUserLocation, in case you ever choose to show user location on the map. I'm also going to explicitly set the canShowCallout, as that's presumably the reason you're writing this method at all.)

Bottom line, if you want to show a simple pin annotation view, use MKPinAnnotationView. Using MKAnnotationView alone will result in no annotations from appearing.

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The standard way to prevent the TextFields from being covered by the keyboard is to move the view up/down whenever the keyboard is shown.

Here is some sample code:

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Ios – Swift – Custom MKAnnotationView, set label title

Make your custom annotation view

There is no public API allowing you to access the label in the pop up directly. What you need to do is make a subclass of MKPinAnnotationView and do whatever customization you want there. As an example,

class CustomAnnotationView : MKPinAnnotationView
{
    let selectedLabel:UILabel = UILabel.init(frame:CGRectMake(0, 0, 140, 38))

    override func setSelected(selected: Bool, animated: Bool)
    {
        super.setSelected(false, animated: animated)

        if(selected)
        {
            // Do customization, for example:
            selectedLabel.text = "Hello World!!"
            selectedLabel.textAlignment = .Center
            selectedLabel.font = UIFont.init(name: "HelveticaBold", size: 15)
            selectedLabel.backgroundColor = UIColor.lightGrayColor()
            selectedLabel.layer.borderColor = UIColor.darkGrayColor().CGColor
            selectedLabel.layer.borderWidth = 2
            selectedLabel.layer.cornerRadius = 5
            selectedLabel.layer.masksToBounds = true

            selectedLabel.center.x = 0.5 * self.frame.size.width;
            selectedLabel.center.y = -0.5 * selectedLabel.frame.height;
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}

Other Notes

Use this custom view in the map view:

func mapView(mapView: MKMapView, viewForAnnotation annotation: MKAnnotation) -> MKAnnotationView? {
    var anno = mapView.dequeueReusableAnnotationViewWithIdentifier("Anno")
    if anno == nil
    {
        anno = CustomAnnotationView.init(annotation: annotation, reuseIdentifier: "Anno")
    }
    return anno;
}

Since the title property of the annotation is not set, you will have to call the map view function selectAnnotation yourself. Add the following to the CustomAnnotationView class:
```
override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
    mapView?.selectAnnotation(self.annotation!, animated: true)
}
```

If you want to have more than one marker on the map:

Usually just draw the annotation simply during initialization. In setSelected just return false (meaning "show all annotations all the time").

class DotAnnotationView : MKPinAnnotationView {

    let dot: UILabel = UILabel.init(frame:CGRect(x: 0, y: 0, width: 20, height: 20))

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        _setup()
    }

    override init(annotation: MKAnnotation?, reuseIdentifier: String?) {
        super.init(annotation: annotation, reuseIdentifier: reuseIdentifier)
        _setup()
    }

    override func prepareForReuse() {
        dot.text = "you forgot to set the text value?"
    }

    override func setSelected(_ selected: Bool, animated: Bool) {
        super.setSelected(false, animated: animated)
    }

    func _setup() {
        dot.textAlignment = .center
        .. etc
    }

}

You set the string (or other values - say color of the panel) for each annotation in mapView#viewFor. It's like populating a cell in a UITableView.

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {

    let textForThisItem = annotation.title!!
    // or, just use index#of to determine which row this is in your data array
    if annotation.isEqual(mkMap.userLocation) {
        // skip the user-position indicator
        return nil
    }

    var anno = mapView.dequeueReusableAnnotationView(withIdentifier: "anno")

    if anno == nil {
        anno = DotAnnotationView.init(annotation: annotation, reuseIdentifier: "anno")
    }

    (anno as! DotAnnotationView).dot.text = textForThisItem

    return anno
}

Finally note that somewhat confusingly, if you very simply change the class of CustomAnnotationView from MKPinAnnotationView to MKAnnotationView, everything works the same but it replaces "all of the pin" rather than just the annotation.