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I am maintaining the CCHMapClusterController mono port.
I did the Unified API migration and now encounter an issue with all annotations on map views.
When panning the map view or changing the region programatically all map view's annotations are replaced by instances of MKAnnotationWrapper.
The library does not override the framework behavior using methods swizzling or categories.
You can download the code of the mono port here : https://github.com/nverinaud/CCHMapClusterController-Mono.
Open the "CCHMapClusterController-Mono/MapClusterSample/MapClusterSample.sln" solution and run the project on simulator or device.
You'll see logs of wrapped annotations.
I can't figure out how this happen. If I do not use the library, just reference it somewhere in the code for it to load it breaks all map views in the app.
Thank you for your help !
It is by design, but the answer is a bit complicated.
When Objective-C calls GetViewForAnnotation, the only thing Xamarin.iOS knows is that the pointer we get is to an object that conforms to MKAnnotation protocol, we do not know anything else about the object. In particular we can't check the actual type of the object at runtime, because Objective-C is known to lie (you could for instance get back that the object is of a type that does not implement the MKAnnotation protocol). This also means that we do not know which C# type to use - we know we need something that implements the IMKAnnotation interface, but we need an actual class that can be instantiated, not an interface. So internally we create Wrapper classes that only implements the I* interfaces, and use those when we get pointers to protocols.
Admittedly we could check if there already is an existing C# object with the desired pointer and which implements the desired interface, but right now we don't (this would also make the behavior less consistent; sometimes you'd get a wrapper object, sometimes not).
The workaround is to lookup the object yourself:
public override MKAnnotationView GetViewForAnnotation(MKMapView mapView,
ACustomAnnotation customAnnotation = Runtime.GetNSObject (annotation.Handle) as ACustomAnnotation;
I hope this makes sense.
Thanks for your help, your snippet work.
What is odd to me is that I only need this trick when the CCHMapClusterController DLL is loaded.
If I create an empty project with a map view and add an MKPointAnnotation to it, Xamarin.iOS does not wrap the annotation.
Are you sure there is no issue in Xamarin.iOS ?
The difference with CCHMapClusterAnnotation is that when GetViewForAnnotation is called by iOS there is no managed instance for the CCHMapClusterAnnotation instance in question. If you add an MKPointAnnotation to a MKMapView, the managed MKPointAnnotation instance already exist, and that's what's passed to the managed GetViewForAnnotation method.