extendedpicker.cs

using System;
using Xamarin.Forms;
using System.Collections;
using System.Reflection;
using System.Collections.Specialized;

namespace XLabs.Forms.Controls
{
	/// <summary>
	/// Extends the Picker Class to add additional features not supported out of the box by Xamarin.
	/// Features Add:
	/// DataBinding
	/// </summary>
	public class ExtendedPicker:Picker
	{
		/// <summary>
		/// Constructor
		/// </summary>
		public ExtendedPicker ()
		{
			base.SelectedIndexChanged += OnSelectedIndexChanged;
		}
		/// <summary>
		/// Identifies the <see cref="P:XLabs.Forms.Controls.ExtendedPicker.SelectedItem" /> property.
		/// </summary>
		public static readonly BindableProperty SelectedItemProperty =    BindableProperty.Create("SelectedItem", typeof(object),     typeof(ExtendedPicker), null, BindingMode.OneWay, null, new BindableProperty.BindingPropertyChangedDelegate(ExtendedPicker.OnSelectedItemChanged), null, null, null);
		/// <summary>
		/// Identifies the <see cref="P:XLabs.Forms.Controls.ExtendedPicker.ItemSource" /> property.
		/// </summary>
		public static readonly BindableProperty ItemsSourceProperty =     BindableProperty.Create("ItemsSource", typeof(IEnumerable), typeof(ExtendedPicker), null, BindingMode.OneWay, null, new BindableProperty.BindingPropertyChangedDelegate(ExtendedPicker.OnItemsSourceChanged), null, null, null);
		/// <summary>
		/// Identifies the <see cref="P:XLabs.Forms.Controls.ExtendedPicker.DisplayProperty" /> property.
		/// </summary>
		public static readonly BindableProperty DisplayPropertyProperty = BindableProperty.Create("DisplayProperty", typeof(string),  typeof(ExtendedPicker), null, BindingMode.OneWay, null, new BindableProperty.BindingPropertyChangedDelegate(ExtendedPicker.OnDisplayPropertyChanged), null, null, null);

		/// <summary>
		/// Accepts an <see cref="T:System.Collections.IList" /> which is used to populate the picker with data. 
		/// By default the <see cref="System.Object.ToString"/> is displayed.
		/// </summary>
		/// <value>The items source.</value>
		public IList ItemsSource
		{
			get
			{
				return (IList)base.GetValue(ExtendedPicker.ItemsSourceProperty);
			}
			set
			{
				base.SetValue(ExtendedPicker.ItemsSourceProperty, value);
			}
		}
		/// <summary>
		/// Sets the item currently displayed in the UI. 
		/// This works by finding the index of the item in the backing data and then updateing <see cref="P:Xamarin.Forms.Picker.SelectedIndex" />  
		/// so the two object need the same ref. 
		/// </summary>
		/// <value>The selected item.</value>
		public object SelectedItem
		{
			get
			{
				return base.GetValue(ExtendedPicker.SelectedItemProperty);
			}
			set
			{
				base.SetValue(ExtendedPicker.SelectedItemProperty, value);
			}
		}
		/// <summary>
		/// A string used in reflection to identify the property to use as the display property of the object. 
		/// If this is not specified the <see cref="System.Object.ToString"/> is used.
		/// </summary>
		/// <value>The display property.</value>
		public string DisplayProperty
		{
			get
			{
				return (string)base.GetValue(ExtendedPicker.DisplayPropertyProperty);
			}
			set
			{
				base.SetValue(ExtendedPicker.DisplayPropertyProperty, value);
			}
		}


		private void OnSelectedIndexChanged(object sender,EventArgs e)
		{
            if (SelectedIndex != -1)
            {
                 this.SelectedItem = ItemsSource[SelectedIndex];
            }
		}


		private static void OnSelectedItemChanged(BindableObject bindable, object oldValue, object newValue)
		{
			ExtendedPicker bindablePicker = (ExtendedPicker)bindable;
			bindablePicker.SelectedItem = newValue;
			if (bindablePicker.ItemsSource != null && bindablePicker.SelectedItem!=null) {
				int count = 0;
				foreach (object obj in bindablePicker.ItemsSource) {
					if (obj == bindablePicker.SelectedItem) {
						bindablePicker.SelectedIndex = count;
						break;
					}
					count++;
				}
			}
		}

		private static void OnDisplayPropertyChanged(BindableObject bindable, object oldValue, object newValue)
		{

			ExtendedPicker bindablePicker = (ExtendedPicker)bindable;
			bindablePicker.DisplayProperty = (string)newValue;
			loadItemsAndSetSelected (bindable);

		}

        static INotifyCollectionChanged observable;
        static ExtendedPicker bindablePicker;
		private static void OnItemsSourceChanged(BindableObject bindable, object oldValue, object newValue)
		{
			bindablePicker = (ExtendedPicker)bindable;
			bindablePicker.ItemsSource = (IList)newValue;
			loadItemsAndSetSelected (bindable);

            observable = newValue as INotifyCollectionChanged;
            if (observable != null)
            {
                observable.CollectionChanged += observable_CollectionChanged;
            }

		}
		static void loadItemsAndSetSelected (BindableObject bindable)
		{
			ExtendedPicker bindablePicker = (ExtendedPicker)bindable;
			if (bindablePicker.ItemsSource as IEnumerable != null) {
				PropertyInfo propertyInfo = null;
				int count = 0;
                if(bindablePicker.Items!=null && bindablePicker.Items.Count>0)
                {
                    bindablePicker.Items.Clear();
                }
				foreach (object obj in (IEnumerable)bindablePicker.ItemsSource) {
					string value = string.Empty;
					if (bindablePicker.DisplayProperty != null) {
						if (propertyInfo == null) {
							propertyInfo = obj.GetType ().GetRuntimeProperty (bindablePicker.DisplayProperty);
							if (propertyInfo == null)
								throw new Exception (String.Concat (bindablePicker.DisplayProperty, " is not a property of ", obj.GetType ().FullName));
						}
						value = propertyInfo.GetValue (obj).ToString();
					}
					else {
						value = obj.ToString();
					}
					bindablePicker.Items.Add (value);
					if (bindablePicker.SelectedItem != null) {
						if (bindablePicker.SelectedItem == obj) {
							bindablePicker.SelectedIndex = count;
						}
					}
					count++;
				}
			}
		}

        static void observable_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            bindablePicker.ItemsSource = (IList)sender;
            loadItemsAndSetSelected(bindablePicker);
        }
	}

}