public static async Task TryExecuteAsync(this IViewModelCommand command, object arg)
 {
     if (command != null && command.CanExecute(arg))
     {
         await command.ExecuteAsync(arg);
     }
 }
 public static async Task TryExecuteAsync(this IViewModelCommand command)
 {
     if (command != null && command.CanExecute())
     {
         await command.ExecuteAsync();
     }
 }