How to define the order of overlapping MKAnnotationViews?

Question

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 bo

Answer 1

I really needed to do this, and none of the (current) answers seemed to provide a reliable implementation. They sort of worked, but panning the map, selecting annotations, or zooming in could mess up the order again.

The final, well behaved solution wasn't so trivial, so I'll just outline the steps I took here. The annotation ordering that MKMapView uses doesn't respect the added order, or even the order of an overriden annotations property. So...

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Steps

• Create a CADisplayLink
• Every frame, reorder annotations using both the layer zPosition, and the view's ordering in the superview's subviews array.
• If the view is selected, promote it to the front in your ordering scheme
• Tapping on annotations still respects internal MKMapView ordering, despite the already made changes. To counter this, add an MKMapViewDelegate
• In the delegate object's mapView:didSelect: method, check if the selected annotation is what you'd like it to be
• You can figure out the correct/prioritised annotation by running hit tests on the annotations yourself, with your own ordering taken into account
• If the selected annotation is correct, great. If not, manually select the correct annotation using selectAnnotation:animated:

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And there you have it. The above method seems to work well, and the performance hit from running this each frame isn't too bad. You could also look at switching to MapBox, which I believe supports annotation ordering, but this isn't always an option for various reasons.