主题：窗口的ComboBox控件问题请教老师

窗口的代码如下

Dim cmd As New SQLCommand
Dim dt As DataTable
Dim cmb As WinForm.ComboBox
cmd.C
cmd.CommandText = "SELECT DISTINCT 供应商 From {供应商资料} Where 删除 = False"
dt = cmd.ExecuteReader()
cmb = e.Form.Controls("ComboBox1")
cmb.ComboList= dt.GetComboListString("供应商")

想在控件列表项目中增加一个空白内容能实现吗?主要用于下拉列表选择空白内容后清除其他控件的值