Hey folks, I’ve noticed some odd behavior when pas...

# ios

[Sargun Vohra]

Hey folks, I’ve noticed some odd behavior when passing references for Kotlin objects to ObjC objects. For example, I’m using the MapLibre pod, which has a UIView called MLNMapView. This view takes a delegate of the MLNMapViewDelegate protocol, which is notified on map movement. So in Kotlin, I implement the MLNMapViewDelegateProtocol interface and set myMapView.delegate to an instance of that implementation. And when the map is moved, I println the new position.

What I’ve found is that after a few seconds, my instance stops getting notified of map movements. But if in Kotlin I maintain a reference to this delegate instance, the problem goes away; my delegate functions indefinitely.

It’s not just the map view delegate; I’ve noticed the same thing passing a Kotlin object as a target to a UIGestureRecognizer. If I don’t hold a reference to my target in Kotlin land somewhere, the gesture recognizer stops working.

Based on the above, I suspect the kotlin object is getting garbage collected when the only reference to it is in an objc object. Is this expected? Should I treat delegates and similar things as weak references only?

[Sargun Vohra]

okay, answered my own question, partially:
• MLNMapView’s delegate is marked as weak in the docs, I just never noticed (or knew that was an objc feature at all)
• UIGestureRecognizer doesn’t say whether it’s weak or not in the docs but I guess I should assume it’s weak

[Andrei Salavei]

You're right. Generally, all delegates/targets/target-action patterns in Obj-C are week-referenced.
From another side, you have to keep in mind that all fields by default are strong in Swift/Obj-C. Hence, reference loops like Kotlin Object 1 -> Swift/Obj-C Object -> Kotlin Object 2 -> Kotlin Object 1 will create memory leaks and cannot be cleared by GC.