Presentation Model (MVVM) Good Practices

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel;
using PresentationModelBase;
using System.Reflection;

namespace App.Configuration.Wpf
{
    //this property will tell if the PresentationModel is doing
    //some work in background
    class IsWorkingPropertyDescriptor : PropertyDescriptor
    {
        public IsWorkingPropertyDescriptor() :
            base(
             TypeDescriptor.CreateProperty
             (typeof(PresentationModel), "IsWorking", typeof(bool), null))
        {
            _propertyChangeNotification = typeof(PresentationModel).GetMethod("OnPropertyChanged", BindingFlags.NonPublic | BindingFlags.Instance);
        }

        MethodInfo _propertyChangeNotification;
        static Dictionary<PresentationModel, bool> _propertyValues = new Dictionary<PresentationModel, bool>();

        public override bool CanResetValue(object component)
        {
            return true;
        }

        public override Type ComponentType
        {
            get { return typeof(PresentationModel); }
        }

        public override object GetValue(object component)
        {
            PresentationModel pm = (PresentationModel)component;
            if (!_propertyValues.ContainsKey(pm))
            {
                _propertyValues.Add(pm, false);
            }
            return _propertyValues[pm];
        }

        public override bool IsReadOnly
        {
            get { return false; }
        }

        public override Type PropertyType
        {
            get { return typeof(bool); }
        }

        public override void ResetValue(object component)
        {
            SetValue(component, false);
        }

        public override void SetValue(object component, object value)
        {
            PresentationModel pm = (PresentationModel)component;
            if (!_propertyValues.ContainsKey(pm))
            {
                _propertyValues.Add(pm, (bool)value);
            }
            else
                _propertyValues[pm] = (bool)value;
            _propertyChangeNotification.Invoke(component, new object[] { "IsWorking" });
        }

        public override bool ShouldSerializeValue(object component)
        {
            return false;
        }
    }
}