iPadOS 13.4 trackpad IUIPointerInteractionDelegate method GetStyleForRegion not being called

Question

I am working on an iPadOS 13.4 app that works with trackpad input. I have gotten a lot of things working, like two-finger scrolling, right-click (two-finger or control-click), pinch-to-zoom, etc. I have another control that works great with the trackpad but it is a custom text control, so I need to change the round cursor from a circle to an I-beam using the UIPointerInteraction APIs.

I modified an Apple-provided Swift sample code project and got an I-beam to appear over a view so I know what to do if the system will call my styleFor: region method, but it just won't call it. The Xamarin APIs are not yet documented for this; the best is the Assembly Browser and the API diffs here that mention the method signatures. I am on Xamarin.iOS 13.16.1.

public class MyClass: UIView, IUIPointerInteractionDelegate {

    ...

    initalization_code() {
        ...
        UIPointerInteraction interaction = new UIPointerInteraction(this);
        this.AddInteraction(interaction);
    }

    public UIPointerStyle GetStyleForRegion(UIPointerInteraction interaction, UIPointerRegion region) {
        // this code is never called
        const float HEIGHT = 30f;
        return UIPointerStyle.Create(UIPointerShape.CreateBeam((nfloat)HEIGHT, UIAxis.Vertical), UIAxis.Vertical);
    }
}

What do I need to do to get iOS to call into my C# code for GetStyleForRegion?

Answer 1

Adding this Export annotation did the job:

[Export("pointerInteraction:styleForRegion:")]
public UIPointerStyle GetStyleForRegion(UIPointerInteraction interaction, UIPointerRegion region) {
    // this code gets called now!
    const float HEIGHT = 30f;
    return UIPointerStyle.Create(UIPointerShape.CreateBeam((nfloat)HEIGHT, UIAxis.Vertical), UIAxis.Vertical);
}

Now the method is called.