public class VM :INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        private string _value;
        public string Value
        {
            get
            {
                return _value;
            }
            set
            {
                _value = value;
                PropertyChanged.Raise("Value");
            }
        }
    }

    public static class EventExtensions
    {
        public static void Raise(this PropertyChangedEventHandler changeEvent, string property)
        {
            changeEvent.Invoke(changeEvent.Target, new PropertyChangedEventArgs(property));;
        }
    }