F# Interface Implementation Error

Question

I'm trying to implement the following interface in F#:

using Foundation;
using ObjCRuntime;
using System;
using System.Runtime.CompilerServices;
using UIKit;

namespace Softweb.Xamarin.Controls.iOS
{
    [Protocol (Name = "ZLSwipeableViewDataSource", WrapperType = typeof(CardViewDataSourceWrapper))]
    public interface ICardViewDataSource : INativeObject, IDisposable
    {
        //
        // Methods
        //
        [Export ("nextViewForSwipeableView:"), Preserve (Conditional = true), CompilerGenerated]
        UIView NextCardForCardView (CardView cardView);
    }
}

To do so I have the following code:

[<Register ("BackgroundAnimationViewControllerDataSource")>]
type BackgroundAnimationViewControllerDataSource () =
    interface ICardViewDataSource with 
         member this.NextCardForCardView(cardView : CardView) = 
            let card = new UIView()
            card.Frame <- CGRect()
            card.BackgroundColor <- UIColor.Blue
            card.Layer.ShouldRasterize <- true
            card 

However this gives me the error:

No implementation was given for 'ObjCRuntime.INativeObject.get_Handle() : nativeint'. Note that all interface members must be implemented and listed under an appropriate 'interface' declaration, eg 'interface ... with member ...'.

I don't understand this as there is no additional methods in the interface.

Answer 1

Note that your ICardViewDataSource interface also implements INativeObject . This means you need to implement all members of that interface too. In this case, there's a property called Handle that is missing.

Also worth noting that it implements IDisposable which means you may need to have a Dispose method too.