[ios] fixes #5129 added annotation property to MGLAnnotationView

[frederoni]

Also added a test case to make sure the annotation property is handled correctly but there's no reference to the platform/ios/test/MGLAnnotationViewTests.m file in the project file as I'm figuring out the details around #4641.

/cc @1ec5 @boundsj @friedbunny

[1ec5]

Nit: use alloc/init rather than new. In general, using init directly makes it easier to add parameters to an initializer. (Admittedly, it used to matter more in the days before ARC.) In this codebase specifically, where many of the files are Objective-C++, we prefer to leave the new keyword to C++ usage.

[1ec5]

#4837 adds a UI test bundle to the iOS project. Until then, you may be able to add this test to the existing unit test bundle, which otherwise only tests non-UI code that's shared between the iOS and OS X SDKs.

[boundsj]

It does not look like there is a good reason for us to use the MK approach of warning about changing this property in the comment but not making it readonly. Let's go ahead and make it readonly.

[1ec5]

I wonder if the reason MapKit leaves this property read-write is that a subclass might want to override -setAnnotation: to do something special. At least, that’s the reason MapKit exposes -setSelected:animated: publicly with a note saying never to call it (as seen in #5297).

[frederoni]

The annotation corresponds to the visibility of the view so it could be useful to override in order to animate the adding of the annotations views. However, I'd also prefer to make this property readonly and maybe expose -mapView:didAddAnnotationViews:

[1ec5]

👍