ViewModelBaseNotifyPropertyChanged.cs

public class ViewModelBase : INotifyPropertyChanged
{
    #region INotifyPropertyChanged Implementation

    public event PropertyChangedEventHandler PropertyChanged = delegate { };
    protected void OnPropertyChanged(string propertyName)
    {
        PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

    #endregion INotifyPropertyChanged Implementation
}