Multi-select in Xamarin in Forms

gistfile1.txt

using System;
using System.Linq;
using Xamarin.Forms;
using System.Collections.Generic;
using System.ComponentModel;

namespace SampleApp
{
  // Inherit from this page to get a multi-select option in XF
	public class SelectMultipleBasePage<T> : ContentPage
	{
		public class WrappedSelection<T> : INotifyPropertyChanged
		{
			public T Item { get; set; }

			bool isSelected = false;
			public bool IsSelected { 
				get {
					return isSelected;
				}
				set
				{
					if (isSelected != value) {
						isSelected = value;
						PropertyChanged (this, new PropertyChangedEventArgs (nameof (IsSelected)));
					}
				}
			}
			public event PropertyChangedEventHandler PropertyChanged = delegate {};
		}

		public class WrappedItemSelectionTemplate : ViewCell
		{
			public WrappedItemSelectionTemplate() : base ()
			{
				Label name = new Label();
				name.SetBinding(Label.TextProperty, new Binding("Item.Name"));

				Switch mainSwitch = new Switch();
				mainSwitch.SetBinding(Switch.IsToggledProperty, new Binding("IsSelected"));

				RelativeLayout layout = new RelativeLayout();
				layout.Children.Add (name, 
					Constraint.Constant (5), 
					Constraint.Constant (5),
					Constraint.RelativeToParent (p => p.Width - 60),
					Constraint.RelativeToParent (p => p.Height - 10)
				);

				layout.Children.Add (mainSwitch, 
					Constraint.RelativeToParent (p => p.Width - 55), 
					Constraint.Constant (5),
					Constraint.Constant (50),
					Constraint.RelativeToParent (p => p.Height - 10)
				);

				View = layout;
			}
		}

		public List<WrappedSelection<T>> WrappedItems = new List<WrappedSelection<T>>();

		public SelectMultipleBasePage(List<T> items)
		{
			WrappedItems = items.Select (item => new WrappedSelection<T> () { Item = item, IsSelected = false }).ToList ();

			ListView mainList = new ListView () {
				ItemsSource = WrappedItems,
				ItemTemplate = new DataTemplate (typeof(WrappedItemSelectionTemplate))
			};

			Content = mainList;

			ToolbarItems.Add (new ToolbarItem ("All", null, SelectAll, ToolbarItemOrder.Primary));
			ToolbarItems.Add (new ToolbarItem ("None", null, SelectNone, ToolbarItemOrder.Primary));
		}

		void SelectAll ()
		{
			foreach (var wi in WrappedItems)
				wi.IsSelected = true;
		}

		void SelectNone ()
		{
			foreach (var wi in WrappedItems)
				wi.IsSelected = false;
		}

		public List<T> GetSelection() 
		{
			return WrappedItems.Where (item => item.IsSelected).Select (wrappedItem => wrappedItem.Item).ToList ();	
		}
	}
}