A real quickie example of a UIPickerView: (iOS SDK)

Add a UIPickerView to your xib or Storyboard called slotMachineView and a label (named selectedLbl) to show the currently selected items.

using System;
using UIKit;

namespace Slots
{
    public partial class ViewController : UIViewController
    {
        public ViewController (IntPtr handle) : base (handle)
        {
        }

        public override void ViewDidLoad ()
        {
            base.ViewDidLoad ();
                slotMachineView.Model = new StackOverflowModel (selectedLbl);
        }

        public override void DidReceiveMemoryWarning ()
        {
            base.DidReceiveMemoryWarning ();
        }
    }

    public class StackOverflowModel : UIPickerViewModel
    {
        static string[] names = new string [] {
            "pscorlib.dll",
            "pscorlib_aot.dll",
            "Mono.PlayScript.dll",
            "PlayScript.Dynamic.dll",
            "PlayScript.Dynamic_aot.dll",
            "PlayScript.Optimization.dll",
            "playshell.exe",
            "psc.exe"
        };

        UILabel lbl;

        public StackOverflowModel (UILabel lbl)
        {
            this.lbl = lbl;
        }

        public override nint GetComponentCount (UIPickerView v)
        {
            return 3;
        }

        public override nint GetRowsInComponent (UIPickerView pickerView, nint component)
        {
            return names.Length;
        }

        public override string GetTitle (UIPickerView picker, nint row, nint component)
        {
            switch (component) {
            case 0:
                return names [row];
            case 1:
                return row.ToString ();
            case 2:
                return new string ((char)('A' + row), 1);
            default:
                throw new NotImplementedException ();
            }
        }

        public override void Selected (UIPickerView picker, nint row, nint component)
        {
            lbl.Text = String.Format ("{0} : {1} : {2}",
                names [picker.SelectedRowInComponent (0)],
                picker.SelectedRowInComponent (1),
                picker.SelectedRowInComponent (2));
        }

        public override nfloat GetComponentWidth (UIPickerView picker, nint component)
        {
            if (component == 0)
                return 220f;
            else
                return 30f;
        }
    }
}

From my answer on StackOverflow.