WPF, SDI linked window base class or don't miss your windows

// --------------------------------------------------------------------------------------------------------------------
// <copyright file="CommandManagerHelper.cs" company="JAGG">
//   JAGG
// </copyright>
// <summary>
//  This class is for command manipulation at the view model.
// </summary>
// --------------------------------------------------------------------------------------------------------------------
namespace MvvmSupport
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Windows.Input;

    /// <summary>
    /// This class is for command manipulation at the view model.
    /// </summary>
    internal class CommandManagerHelper
    {
        #region Constructors

        /// <summary>
        /// Prevents a default instance of the <see cref="CommandManagerHelper"/> class from being created. 
        /// </summary>
        private CommandManagerHelper()
        {
        }

        #endregion Constructors

        #region Methods

        /// <summary>
        /// Add handlers to command execution.
        /// </summary>
        /// <param name="handlers">Handlers to execute commands.</param>
        internal static void AddHandlersToRequerySuggested(List<WeakReference> handlers)
        {
            if (handlers != null)
            {
                foreach (var handler in handlers.Select(handlerRef => handlerRef.Target).OfType<EventHandler>())
                {
                    CommandManager.RequerySuggested += handler;
                }
            }
        }

        /// <summary>
        /// Add the handlers list to the lost of handlers of the same type.
        /// </summary>
        /// <param name="handlers">List that contain the handlers.</param>
        /// <param name="handler">Event to add the handlers.</param>
        internal static void AddWeakReferenceHandler(ref List<WeakReference> handlers, EventHandler handler)
        {
            AddWeakReferenceHandler(ref handlers, handler, -1);
        }

        /// <summary>
        /// Add a handler to the list of the same type.
        /// </summary>
        /// <param name="handlers">List with the handlers.</param>
        /// <param name="handler">Event handler..</param>
        /// <param name="defaultListSize">List size.</param>
        internal static void AddWeakReferenceHandler(
            ref List<WeakReference> handlers, EventHandler handler, int defaultListSize)
        {
            if (handlers == null)
            {
                handlers = defaultListSize > 0 ? new List<WeakReference>(defaultListSize) : new List<WeakReference>();
            }

            handlers.Add(new WeakReference(handler));
        }

        /// <summary>
        /// Call the command handlers.
        /// </summary>
        /// <param name="handlers">Handlers list.</param>
        internal static void CallWeakReferenceHandlers(List<WeakReference> handlers)
        {
            if (handlers != null)
            {
                var callees = new EventHandler[handlers.Count];
                var count = 0;

                for (int i = handlers.Count - 1; i >= 0; i--)
                {
                    WeakReference reference = handlers[i];
                    var handler = reference.Target as EventHandler;
                    if (handler == null)
                    {
                        handlers.RemoveAt(i);
                    }
                    else
                    {
                        callees[count] = handler;
                        count++;
                    }
                }

                for (int i = 0; i < count; i++)
                {
                    var handler = callees[i];
                    handler(null, EventArgs.Empty);
                }
            }
        }

        /// <summary>
        /// Remove the handlers for the list.
        /// </summary>
        /// <param name="handlers">List with the hsandlers.</param>
        internal static void RemoveHandlersFromRequerySuggested(List<WeakReference> handlers)
        {
            if (handlers != null)
            {
                foreach (var handler in handlers.Select(handlerRef => handlerRef.Target).OfType<EventHandler>())
                {
                    CommandManager.RequerySuggested -= handler;
                }
            }
        }

        /// <summary>
        /// Remove a specific handle for the list of command handlers.
        /// </summary>
        /// <param name="handlers">List of command handles.</param>
        /// <param name="handler">Handler to be removed.</param>
        internal static void RemoveWeakReferenceHandler(List<WeakReference> handlers, EventHandler handler)
        {
            if (handlers != null)
            {
                for (int i = handlers.Count - 1; i >= 0; i--)
                {
                    WeakReference reference = handlers[i];
                    var existingHandler = reference.Target as EventHandler;
                    if ((existingHandler == null) || (existingHandler == handler))
                    {
                        // Remove all h.andlers added before this.
                        handlers.RemoveAt(i);
                    }
                }
            }
        }

        #endregion Methods
    }
}