Exception when zooming with overlays on MKMapView: NSInvalidArgumentException NSSetM removeObject: object cannot be nil

Question

I am adding around 1000 MKPolygons onto an MKMapView. After adding the overlays onto the MKMapView it works fine. However if I zoom in and

Answer 1

I had a very similar problem when adding & removing annotations to a map view.

The answer turned out to be put everything that accesses the annotations - even calculations that only read the annotations array - onto the main thread.

I had only put the actual adding & removing on the main thread and it was ok for the most part, but would randomly crash with

[__NSSetM removeObject:]: object cannot be nil