Hi Danny, 

Thanks for the sample!

Basically, Xamarin.iOS has a couple ways of creating gestures, and the way you're using unfortunately isn't compatible for being called by the obj-c runtime. However, its actually quite simple to make that adjustment. 

Here's a link that shows they way you need to do it: http://dan.clarke.name/2012/08/using-uigesturerecognizer-in-monotouch/

Also, i've modified your code to this:

        public override void InitializeCell(IGGridView gridView, IGGridViewCell cell)
        {
            var path = gridView.ResolvePathForCell(cell);

            if (path.IsFixed == IGGridViewFixedColumnDirection.IGGridViewFixedColumnDirectionNone)
            {
                var tapGesture = new UITapGestureRecognizer(this, new MonoTouch.ObjCRuntime.Selector("HandleInput"));
                //var tapGesture = new UITapGestureRecognizer(HandleInput) { NumberOfTapsRequired = 1};

                cell.RegisterGestures(new[] { tapGesture });
            }
        }

        [Export("HandleInput")]
        private void HandleInput(UITapGestureRecognizer gestureRecognizer)
        {
            var cell = gestureRecognizer.View as IGGridViewCell;

            var viewController = new UIViewController();
            var textField = new UITextField(viewController.View.Bounds) { AutoresizingMask = ~UIViewAutoresizing.None, Text = cell.TextLabel.Text };
            viewController.View.AddSubview(textField);
            var popover = new UIPopoverController(viewController);
            popover.PresentFromRect(cell.Bounds, cell, UIPopoverArrowDirection.Any, true);
        }

Hope this helps. Don't hesitate if you have any more questions. 

-SteveZ