Objective C: (NSSet *)annotationsInMapRect:(MKMapRect) mapRect method returns null value

I am trying to implement the following method in my application

NSSet *nearbySet = [self.mapView annotationsInMapRect:self.mapView.visibleMapRect];

I see in my mapView there ar开发者_运维问答e 4 annotations, however, the method returns me 0 values in the set.

Can anyone advise if I have missed out on anything here?

Thanks in advance.

Zhen

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Three quick things to check as a "sanity check":

1. What is the value of self.mapView? Make sure it isn't nil.
2. What does self.mapView.annotations contain?
3. What is the value of self.mapView.visibleMapRect?