Catel - Part 4 of n: Unit testing with Catel

// --------------------------------------------------------------------------------------------------------------------
// <copyright file="Dispatcherhelper.cs" company="Catel development team">
//   Copyright (c) 2008 - 2011 Catel development team. All rights reserved.
// </copyright>
// <summary>
//   Helper to force a refresh for the WPF form/control
// </summary>
// --------------------------------------------------------------------------------------------------------------------

using System.Windows.Threading;

namespace Catel.Windows
{
	/// <summary>
	/// Helper to force a refresh for the WPF form/control
	/// </summary>
	/// <remarks>
	/// Refrence:
	/// http://social.msdn.microsoft.com/forums/en-US/wpf/thread/a2988ae8-e7b8-4a62-a34f-b851aaf13886#app_doevents
	/// </remarks>
	public class DispatcherHelper
	{
		private static DispatcherOperationCallback exitFrameCallback = ExitFrame;

		/// <summary>
		/// Processes all UI messages currently in the message queue.
		/// </summary>
		public static void DoEvents()
		{
			// Create new nested message pump.
			DispatcherFrame nestedFrame = new DispatcherFrame();

			// Dispatch a callback to the current message queue, when getting called,
			// this callback will end the nested message loop.
			// note that the priority of this callback should be lower than that of UI event messages.
			DispatcherOperation exitOperation = Dispatcher.CurrentDispatcher.BeginInvoke(
				DispatcherPriority.Background, exitFrameCallback, nestedFrame);

			// pump the nested message loop, the nested message loop will immediately
			// process the messages left inside the message queue.
			Dispatcher.PushFrame(nestedFrame);

			// If the "exitFrame" callback is not finished, abort it.
			if (exitOperation.Status != DispatcherOperationStatus.Completed)
			{
				exitOperation.Abort();
			}
		}

		private static object ExitFrame(object state)
		{
			DispatcherFrame frame = state as DispatcherFrame;

			// Exit the nested message loop.
			frame.Continue = false;

			return null;
		}
	}  
}