数据源绑定下拉框默认值问题！

用数据源绑定下拉框时，下拉框第一项要默认为空！，必须要设置其AppendDataBoundItems 属性为true.

< asp:ObjectDataSource ID ="ObjectDataSource1" runat ="server" OldValuesParameterFormatString ="original_{0}"

SelectMethod ="GetIw_BaseChild" TypeName ="BLL.Iw_BaseChild" >

< SelectParameters >

< asp:Parameter DefaultValue ="dwly" Name ="pCode" Type ="String" />

</ SelectParameters >

</ asp:ObjectDataSource >

< asp:DropDownList ID ="ddlUnitSource" runat ="server" DataSourceID ="ObjectDataSource1" DataTextField ="name" DataValueField ="id" AppendDataBoundItems="True" >

< asp:ListItem Value ="0" > 无 </ asp:ListItem >

</ asp:DropDownList >

看到反绿的那个属性吗？就设置它为true就行了！