使用Async-await级联ComboBox不起作用

Question

我有这段代码使用异步方法填充了三个组合框

    private async void FrmEmployee_Load(object sender, EventArgs e)
    {
        cmbCountry.Properties.DataSource =await emp.GetCountry();
        cmbCountry.Properties.DisplayMember = "Nom";
        cmbCountry.Properties.ValueMember = "ID_Country";
    }
    private async void cmbCity_Enter(object sender, EventArgs e)
    {
            cmbCity.Properties.DataSource =await emp.GetCity(Convert.ToInt32(cmbCountry.EditValue));
            cmbCity.Properties.DisplayMember = "Willaya";
            cmbCity.Properties.ValueMember = "Numéro";
    }

    private async void cmbTown_Enter(object sender, EventArgs e)
    {
            cmbTown.Properties.DataSource =await emp.GetTown(Convert.ToInt32(cmbCity.EditValue));
            cmbTown.Properties.DisplayMember = "Commune";
            cmbTown.Properties.ValueMember = "ID_Town";
    }

并且我有这段代码可在gridView的DoubleClick上触发

private async void gridView1_DoubleClick(object sender, EventArgs e)
    {         
            cmbCountry.Text = gridView1.GetRowCellValue(gridView1.FocusedRowHandle, "Pays").ToString();
            cmbCity_Enter(sender, e);
            cmbCity.Text = gridView1.GetRowCellValue(gridView1.FocusedRowHandle, "Willaya").ToString();
            cmbTown_Enter(sender, e);
            cmbTown.Text = gridView1.GetRowCellValue(gridView1.FocusedRowHandle, "Commune").ToString();
    }

在我将此代码与同步一起使用之前，该代码非常有效，但现在与async不兼容，这是为什么？以及如何解决此问题，谢谢。