Creating an Animated ContentControl

// <copyright file="RelayCommand.cs" company="GalaSoft Laurent Bugnion">
// Copyright © GalaSoft Laurent Bugnion 2009-2010
// </copyright>
// ****************************************************************************
// <author>Laurent Bugnion</author>
// <email>laurent@galasoft.ch</email>
// <date>22.4.2009</date>
// <project>GalaSoft.MvvmLight</project>
// <web>http://www.galasoft.ch</web>
// <license>
// See license.txt in this project or http://www.galasoft.ch/license_MIT.txt
// </license>
// <LastBaseLevel>BL0008</LastBaseLevel>
// ****************************************************************************
// <credits>This class was developed by Josh Smith (http://joshsmithonwpf.wordpress.com) and
// slightly modified with his permission.</credits>
// ****************************************************************************

using System;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Windows.Input;

////using GalaSoft.Utilities.Attributes;

namespace GalaSoft.MvvmLight.Command
{
    /// <summary>
    /// A command whose sole purpose is to relay its functionality to other
    /// objects by invoking delegates. The default return value for the CanExecute
    /// method is 'true'.  This class does not allow you to accept command parameters in the
    /// Execute and CanExecute callback methods.
    /// </summary>
    ////[ClassInfo(typeof(RelayCommand),
    ////  VersionString = "3.0.0.0",
    ////  DateString = "201003041420",
    ////  Description = "A command whose sole purpose is to relay its functionality to other objects by invoking delegates.",
    ////  UrlContacts = "http://www.galasoft.ch/contact_en.html",
    ////  Email = "laurent@galasoft.ch")]
    public class RelayCommand : ICommand
    {
        private readonly Action _execute;

        private readonly Func<bool> _canExecute;

        /// <summary>
        /// Initializes a new instance of the RelayCommand class that 
        /// can always execute.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        /// <exception cref="ArgumentNullException">If the execute argument is null.</exception>
        public RelayCommand(Action execute)
            : this(execute, null)
        {
        }

        /// <summary>
        /// Initializes a new instance of the RelayCommand class.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        /// <param name="canExecute">The execution status logic.</param>
        /// <exception cref="ArgumentNullException">If the execute argument is null.</exception>
        public RelayCommand(Action execute, Func<bool> canExecute)
        {
            if (execute == null)
            {
                throw new ArgumentNullException("execute");
            }

            _execute = execute;
            _canExecute = canExecute;
        }

#if SILVERLIGHT
        /// <summary>
        /// Occurs when changes occur that affect whether the command should execute.
        /// </summary>
        public event EventHandler CanExecuteChanged;
#else
        /// <summary>
        /// Occurs when changes occur that affect whether the command should execute.
        /// </summary>
        public event EventHandler CanExecuteChanged
        {
            add
            {
                if (_canExecute != null)
                {
                    CommandManager.RequerySuggested += value;
                }
            }

            remove
            {
                if (_canExecute != null)
                {
                    CommandManager.RequerySuggested -= value;
                }
            }
        }
#endif

        /// <summary>
        /// Raises the <see cref="CanExecuteChanged" /> event.
        /// </summary>
        [SuppressMessage("Microsoft.Performance", "CA1822:MarkMembersAsStatic",
            Justification = "The this keyword is used in the Silverlight version")]
        [SuppressMessage("Microsoft.Design", "CA1030:UseEventsWhereAppropriate",
            Justification = "This cannot be an event")]
        public void RaiseCanExecuteChanged()
        {
#if SILVERLIGHT
            var handler = CanExecuteChanged;
            if (handler != null)
            {
                handler(this, EventArgs.Empty);
            }
#else
            CommandManager.InvalidateRequerySuggested();
#endif
        }

        /// <summary>
        /// Defines the method that determines whether the command can execute in its current state.
        /// </summary>
        /// <param name="parameter">This parameter will always be ignored.</param>
        /// <returns>true if this command can be executed; otherwise, false.</returns>
        [DebuggerStepThrough]
        public bool CanExecute(object parameter)
        {
            return _canExecute == null ? true : _canExecute();
        }

        /// <summary>
        /// Defines the method to be called when the command is invoked. 
        /// </summary>
        /// <param name="parameter">This parameter will always be ignored.</param>
        public void Execute(object parameter)
        {
            _execute();
        }
    }
}