does Mapkit on IOS support dequeuing of overlays? (like it does annotations)

Question

Does Mapkit on IOS support dequeuing of overlays? (like it does annotations). If so what is the code for achieving this?

Background: With annotations I believe you can add many, leaving MapKit to instantiate views when required for them via the dequeuing approach. What about the same thing for overlays however if I have many across the country? Do I need to write the code for checking which overlays I have are visible or not and then instantiate them / remove them myself in realtime?

Answer 1

Map Kit does not support reuse of overlays in the same way it supports doing this for annotation views. One of the reasons for this must certainly be that the two objects are not analogous. Overlays are model objects that represent an area on the map, whereas annotation views are view objects used from time to time to display the location of an annotation on the map. The technique of reusing view objects (as opposed to creating individual ones for every use) is an optimization that is used in a couple of other places in UIKit, notably for Table View Cells and various bits of Collection Views.

The view reuse pattern is to establish some data index (table index paths, map coordinates) and then have a delegate provide an appropriate view object to use when a particular index/location comes into view. When the data object passes out of sight, the view object is recycled in a queue.

An annotation is analogous to an overlay, and MapKit does not provide reuse for them either and for good reason: they are the data that is being displayed!

The analogous object to the annotation view is an overlay renderer, which (of course!) provides rendering for an overlay. I assume that the reason these are not reused is because they are not view system objects and presumably much more lightweight, so there is little benefit from reuse. We find evidence for this in the fact that until iOS 7.0 the MapView delegate did provide a view object for overlays and this was replaced by the renderer concept.

I hope that helps.

What problem is this causing for you?