How to define the order of overlapping MKAnnotationViews?

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I have several MKAnnotations (and their corresponding views) in my map, and it sometimes gets really crowded. Now, the annotations in my app come in two flavors: some are bound to stay where they are, while others will move as time goes on. I'd prefer to have the more stable ones visually in the background and the moving ones to always pass in front of them.

One would think, perhaps, that the annotations most recently added to the map would end up to the front (or alternatively at the very back, at least) but this just doesn't seem to be the rule. As far as I can tell, I create and add ALL the non-moving annotations first, and then add some newly-instantiated moving annotations, but many of them (although not all!) end up drawn under the perpetually stock-still ones.

Interestingly, when time goes by, and yet new moving annotations are created, they tend to gravitate more to the top than the first ones - even if all moving annotation objects were created only after the nonmoving parts were already added to the map.

Does anyone know a trick to alter this strange natural order of the annotation views on the map? I tried to search the Map Kit API, but it doesn't seem to speak of such a thing.

mapkit iphone
7 Answers

Ok, so for solution use method from MKMapViewDelegate


- (void)mapView:(MKMapView *)mapView didAddAnnotationViews:(NSArray *)views

In this method you should rearrange AnnotationView after it was added to mapKit View. So, code may looks like this:


- (void)mapView:(MKMapView *)mapView didAddAnnotationViews:(NSArray *)views {
   for (MKAnnotationView * annView in views) {
      TopBottomAnnotation * ann = (TopBottomAnnotation *) [annView annotation];
      if ([ann top]) {
         [[annView superview] bringSubviewToFront:annView];
      } else {
         [[annView superview] sendSubviewToBack:annView];
      }
   }

}

This works for me.

user_1041700

Under iOS 11 the implementation of displayPriority broke all the solutions which use bringSubviewToFront or zPosition.

If you override the annotation view's CALayer, you can wrestle control of zPosition back from the OS.

class AnnotationView: MKAnnotationView {

    /// Override the layer factory for this class to return a custom CALayer class
    override class var layerClass: AnyClass {
        return ZPositionableLayer.self
    }

    /// convenience accessor for setting zPosition
    var stickyZPosition: CGFloat {
        get {
            return (self.layer as! ZPositionableLayer).stickyZPosition
        }
        set {
            (self.layer as! ZPositionableLayer).stickyZPosition = newValue
        }
    }

    /// force the pin to the front of the z-ordering in the map view
   func bringViewToFront() {
        superview?.bringSubviewToFront(toFront: self)
        stickyZPosition = CGFloat(1)
    }

    /// force the pin to the back of the z-ordering in the map view
   func setViewToDefaultZOrder() {
        stickyZPosition = CGFloat(0)
    }

}

/// iOS 11 automagically manages the CALayer zPosition, which breaks manual z-ordering.
/// This subclass just throws away any values which the OS sets for zPosition, and provides
/// a specialized accessor for setting the zPosition
private class ZPositionableLayer: CALayer {

    /// no-op accessor for setting the zPosition
    override var zPosition: CGFloat {
        get {
            return super.zPosition
        }
        set {
            // do nothing
        }
    }

    /// specialized accessor for setting the zPosition
    var stickyZPosition: CGFloat {
        get {
            return super.zPosition
        }
        set {
            super.zPosition = newValue
        }
    }
}
user_3207370

In the delegate function, you can select the pin to force it on top:

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView?` {
    ...
    if my annotation is the special one {
        annotationView.isSelected = true
    }
    ...
}
user_2353340
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