A Picker-control for Xamarin.Forms which enables data binding through an ItemsSource and the SelectedItem.

BindablePicker.cs

using System;
using Xamarin.Forms;
using System.Collections;

namespace YourNamespace.Views.Controls {
	public class BindablePicker : Picker
	{
		public BindablePicker()
		{
			this.SelectedIndexChanged += OnSelectedIndexChanged;
		}

		public static BindableProperty ItemsSourceProperty =
			BindableProperty.Create<BindablePicker, IEnumerable>(o => o.ItemsSource, default(IEnumerable), propertyChanged: OnItemsSourceChanged);

		public static BindableProperty SelectedItemProperty =
			BindableProperty.Create<BindablePicker, object>(o => o.SelectedItem, default(object),propertyChanged: OnSelectedItemChanged);

		public IEnumerable ItemsSource
		{
			get { return (IEnumerable)GetValue(ItemsSourceProperty); }
			set { SetValue(ItemsSourceProperty, value); }
		}

		public object SelectedItem
		{
			get { return (object)GetValue(SelectedItemProperty); }
			set { SetValue(SelectedItemProperty, value); }
		}

		private static void OnItemsSourceChanged(BindableObject bindable, IEnumerable oldvalue, IEnumerable newvalue)
		{
			var picker = bindable as BindablePicker;
			picker.Items.Clear();
			if (newvalue != null)
			{
				//now it works like "subscribe once" but you can improve
				foreach (var item in newvalue)
				{
					picker.Items.Add(item.ToString());
				}
			}
		}

		private void OnSelectedIndexChanged(object sender, EventArgs eventArgs)
		{
			if (SelectedIndex < 0 || SelectedIndex > Items.Count - 1)
			{
				SelectedItem = null;
			}
			else
			{
				SelectedItem = Items[SelectedIndex];
			}
		}

		private static void OnSelectedItemChanged(BindableObject bindable, object oldvalue, object newvalue)
		{
			var picker = bindable as BindablePicker;
			if (newvalue != null)
			{
				picker.SelectedIndex = picker.Items.IndexOf(newvalue.ToString());
			}
		}
	}
}

I think this implementation has a bug! Line 53 in the code listing at the top sets the SelectedItem to Items[SelectedIndex]. This is wrong as Items[] is the base class Picker collection which are STRINGS. The user of this BindablePicker class will expect the SelectedItem to be one of the items that he supplied in the ItemsSource property which is an object. Therefore, Line 53 should set SelectedItem to ItemsSource[SelectedIndex] which also requires changing ItemsSource from IEnumerable to IList.

See this Xamarin forum post for more details:

http://forums.xamarin.com/discussion/70172/bindable-picker-control-not-updating-bound-property#latest

Hi guys,
I have a problem when I try to bind. The error is:

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.

I can't understand why.
Thank you in advance,