下拉列表上的默认选择

Question

我有一个从下拉列表中选择的名称列表。名称正在从数据源中取出，而不是从ListItem中取出。我想在没有选择的情况下将框留空。我怎样才能做到这一点？

<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" 
    DataSourceID="SqlDataSource2" DataTextField="director" 
    DataValueField="director"> 
    <!--<asp:ListItem Text="Please Select Director" Value="-1"/>--> 
</asp:DropDownList> 
<asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ 
    ConnectionStrings:dvdsConnectionString %>" ProviderName="<%$ 
    ConnectionStrings:dvdsConnectionString.ProviderName %>" 
    SelectCommand="SELECT [director] FROM [dvds]"> 
</asp:SqlDataSource> 

Answer 1

尝试添加AppendDataBoundItems="True"的标签，并添加<asp:ListItem Selected="True"></asp:ListItem>作为项目

<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" 
    DataSourceID="SqlDataSource2" DataTextField="director" 
    DataValueField="director" AppendDataBoundItems="True"> 

    <asp:ListItem Selected="True"></asp:ListItem> 

</asp:DropDownList> 
<asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ 
    ConnectionStrings:dvdsConnectionString %>" ProviderName="<%$ 
    ConnectionStrings:dvdsConnectionString.ProviderName %>" 
    SelectCommand="SELECT [director] FROM [dvds]"> 
</asp:SqlDataSource>