list集合添加到下拉框

cboClassName.DataSource = objClassService.GetClassList();
cboClassName.DisplayMember = "ClassName";//设置下拉框显示的文本
cboClassName.ValueMember = "ClassId";//设置下拉框显示文本对应的Value

cboClassName.SelectedIndex = -1;

注意：把下拉框DropDownStyles属性改为DropDownList,改为不可编辑，默认为可编辑的