public object GetViewModel()
        {
            ExtensionItemEventArgs e = new ExtensionItemEventArgs(ExtensionItemAction.GetViewModel);

            RaiseChanged(e);
            return(e.ViewModel);
        }
        public TViewModel GetViewModel <TViewModel>() where TViewModel : class
        {
            ExtensionItemEventArgs e = new ExtensionItemEventArgs(ExtensionItemAction.GetViewModel);

            RaiseChanged(e);
            return(e.ViewModel as TViewModel);
        }
 protected void RaiseChanged(ExtensionItemEventArgs e)
 {
     Changed?.Invoke(this, e);
 }