WPF UI Focus Behavior Class for MVVM Use (e. g. Caliburn.Micro)

FocusBehavior.cs

//----------------------------------------------------------------------------
// <copyright file="FocusBehavior.cs"
//      company="Johnny CH">
//      Copyright (C) 2012 Johnny CH. All rights reserved.
// </copyright>
// <author>Johnny CH</author>
// <description>A behavior class for UI focus control</description>
// <version>v1.0.0 3/13/2016 5:23:35 PM</version>
//
// Based on: https://social.msdn.microsoft.com/Forums/vstudio/en-US/8b119426-bb3b-4b5b-91e9-7827dfc92771/mvvm-wpf-focus-uilelement-from-viewmodel?forum=wpf
//
//----------------------------------------------------------------------------

namespace RecursiveDescentPoC.Behaviors
{
	using System;
	using System.Windows;
	using System.Windows.Threading;

	/// <summary>
	///		Provides focus management.
	/// </summary>
	public static class FocusBehavior
	{
		/// <summary>
		///		The DependencyProperty for IsFocused property.  
		/// </summary>
		public static readonly DependencyProperty IsFocusedProperty =
			DependencyProperty.RegisterAttached(
				"IsFocused", //EXEMPT:GLOBALIZATION
				typeof(bool),
				typeof(FocusBehavior),
				new FrameworkPropertyMetadata(
					false,
					new PropertyChangedCallback(OnIsFocusedPropertyChanged)));

		/// <summary>
		///		Gets the value of IsFocused on the specified object
		/// </summary>
		/// <param name="element">
		///		The <see cref="DependencyObject"/> to get the IsFocused property.
		/// </param>
		/// <returns>
		///		The text message string for <paramref name="element"/>.
		/// </returns>
		public static bool GetIsFocused(DependencyObject element)
		{
			// TODO ArgumentCheck.IsNotNull(element, "element");

			return (bool)element.GetValue(IsFocusedProperty);
		}

		/// <summary>
		///		Sets the value of IsFocused on the specified object
		/// </summary>
		/// <param name="element">
		///		The <see cref="DependencyObject"/> to set the IsFocused property.
		/// </param>
		/// <param name="value">
		///		The IsFocused value for <paramref name="element"/>.
		/// </param>
		public static void SetIsFocused(DependencyObject element, bool value)
		{
			// TODO ArgumentCheck.IsNotNull(element, "element");

			element.SetValue(IsFocusedProperty, value);
		}

		private static void OnIsFocusedPropertyChanged(DependencyObject element, DependencyPropertyChangedEventArgs args)
		{
			UIElement target = element as UIElement;

			if (target == null)
			{
				return;
			}

			bool isFocused = (bool) args.NewValue;

			if (!isFocused)
			{
				return;
			}

			// Delay the call to allow the current batch of processing to finish before we shift focus.
			target.Dispatcher.BeginInvoke(
				(Action) (() =>
				{
					if (target.Focusable)
					{
						target.Focus();

					}
				}),
				DispatcherPriority.Input);
		}
	}
}