MainActivity.cs

using System;

using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;

namespace bom1
{
	[Activity (Label = "bom1", MainLauncher = true, Icon = "@drawable/icon")]
	public class MainActivity : Activity
	{
		int count = 1;
		DateTime _date;
		protected override void OnCreate (Bundle bundle)
		{
			base.OnCreate (bundle);

			// Set our view from the "main" layout resource
			SetContentView (Resource.Layout.Main);

			// Get our button from the layout resource,
			// and attach an event to it
			Button button = FindViewById<Button> (Resource.Id.myButton);
			
			button.Click += delegate {
				button.Text = string.Format ("{0} clicks!", count++);
				ShowDialog (0);
			};

			_date = DateTime.Today;
			button.Text = _date.ToString ("d");

			var editText = FindViewById<EditText> (Resource.Id.editText);
			var textView = FindViewById<TextView> (Resource.Id.textView);
			editText.TextChanged += (object sender, Android.Text.TextChangedEventArgs e) => {
				textView.Text = e.Text.ToString ();
			};
		}

		protected override Dialog OnCreateDialog (int id)
		{
			return new DatePickerDialog (this, HandleDateSet, _date.Year,
				_date.Month - 1, _date.Day);
		}

		void HandleDateSet (object sender, DatePickerDialog.DateSetEventArgs e)
		{
			_date = e.Date;
			var button = FindViewById<Button> (Resource.Id.myButton);
			button.Text = _date.ToString ("d");
		}

	}
}