private string _LastCustomer = "";
private DataTable _LastCustomerTable = null;

private void txtDomain_QueryPopUp(object sender, CancelEventArgs e)
{
    if (this.IsAddOrEditMode)
    {
        string customer = txtCustomerCode.EditValue.ToStringEx();

        if (String.IsNullOrWhiteSpace(customer))
            Assertion.AssertEditorEmpty(txtCustomerCode, "请选择客户！", true);

        //当更换的客户，重新绑定ComboBox数据源
        if (_LastCustomer != customer)
        {
            //获取客户的域名
            _LastCustomerTable = _BLLInstance.GetDomains(customer);
            _LastCustomer = customer;

            //动态绑定域名
            DataBinderTools.BoundComboBox(txtDomain, _LastCustomerTable, "Domain");
        }                
    }
}