Simple Asynchronous Background Task Processing with Progress Dialog (Silverlight Solution)

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace AsyncOperation
{
    public class DefaultProgressDlg : ChildWindow
    {
        public event EventHandler Cancelled;

        public DefaultProgressDlg()
        {
            this.HasCloseButton = false;
            
            //default size. inherited dialogs override it in the xaml.
            this.Width = 300;
            this.Height = 200;
        }

        public void EnableCancelButton(bool enabled)
        {
            //check if dialog supports cancel button
            if (CancelButton == null)
                return;

            //set visibility
            if (enabled)
                CancelButton.Visibility = Visibility.Visible;
            else
                CancelButton.Visibility = Visibility.Collapsed;

            //subscribe CancelButton click event
            CancelButton.Click += new RoutedEventHandler(CancelButton_Click);
        }

        private void CancelButton_Click(object sender, RoutedEventArgs e)
        {
            if (Cancelled != null)
                Cancelled(this, EventArgs.Empty);
        }

        protected virtual Button CancelButton
        {
            get { return null; }
        }

        protected void PostMessage(Delegate del, params object[] args)
        {
            //marhsal to ui thread if needed
            if (!this.Dispatcher.CheckAccess())
            {
                this.Dispatcher.BeginInvoke(del, args);
            }
            else
            {
                del.DynamicInvoke(args);
            }
        }

         //individual message handlers
        private void OnCloseWindow()
        {
            base.Close();
        }

        private void OnSetTitle(string text)
        {
            this.Title = text;
        }

        //public typesafe message senders
        public void CloseWindow()
        {
            Action a = new Action(OnCloseWindow);
            PostMessage(a, null);
        }

        public void SetTitle(string text)
        {
            Action<string> a = new Action<string>(OnSetTitle);
            PostMessage(a, text);
        }
    }
}