public static async Task<TDialog> GetDialogAsync<TDialog>(MetroWindow owner) where TDialog : BaseMetroDialog
{
    TDialog dialog = null;
    await owner.Dispatcher.BeginInvoke(new Action(() =>
    {
        if (owner.metroDialogContainer.Children.Count != 0)
            dialog = owner.metroDialogContainer.Children[0] as TDialog;
    }));
    return dialog;
}