如何让DropDownList 绑定null（空值）

静态声明：

<asp:DropDownList ID="DropDownList1" runat="server" DataSourceID="ObjectDataSource1"

 
                    DataTextField="Name" DataValueField="ID" SelectedValue='<%# Bind("ParentID") %>'
 
                    Style="position: relative" AppendDataBoundItems="True">
 
                   <asp:ListItem Value="">(无 或 空 或 all)</asp:ListItem><!--需要增加的内容-->
 
 </asp:DropDownList>

 

动态添加：

<asp:DropDownList ID="DropDownList1" runat="server" DataSourceID="ObjectDataSource1"

 
                    DataTextField="Name" DataValueField="ID" SelectedValue='<%# Bind("ParentID") %>'
 
                    Style="position: relative" AppendDataBoundItems="True">
 
 
 </asp:DropDownList>

以下为包含在GridView中的DropDownList添加一个空值项：

Protected Sub GV_Match_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles GV_Match.RowDataBound
        If (e.Row.RowType = DataControlRowType.Header Or e.Row.RowType = DataControlRowType.DataRow) Then
                 Dim ddl As DropDownList = New DropDownList()
                ddl = e.Row.FindControl("DropDownList1")
                If Not ddl Is Nothing Then
                    ddl.Items.Insert(0,new ListItem("NULL",String.Empty))                End If         End If
 End Sub

注意： 首选静态声明，因为动态绑定在显示空值的时候可能会出现问题。