ItemPage.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Xamarin.Forms;

namespace TrivialDataBindingDemoVS
{
    class ItemPage : ContentPage
    {
        public ItemPage()
        {
            var item = new Item { Title = "First", Description = "1st item" };

            var titleEntry = new Entry()
            {
                HorizontalOptions = LayoutOptions.FillAndExpand
            };

            // specify the source data model
            // this.BindingContext = item; // bind at the page level
            titleEntry.BindingContext = item; // or bind at the view level

            // Pair the source property with the target view property
            titleEntry.SetBinding(Entry.TextProperty, "Title");

            Button buttonDisplay = new Button
            {
                Text = "Display Item Value",
                FontSize = Device.GetNamedSize(NamedSize.Large, typeof(Button)),
                HorizontalOptions = LayoutOptions.Center,
                VerticalOptions = LayoutOptions.Fill
            };

            buttonDisplay.Clicked += async (sender, e) =>
            {
                item.Title = "You won't see this!";
                await DisplayAlert("Item Object", "Title property: " + item.Title.ToString(), "OK");
            };

            Content = new StackLayout
            {
                Children = { titleEntry, buttonDisplay }
            };
        }
    }
}