如何在GridView EditTemplate中设置DropDownList的SelectedValue

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" OnRowEditing="GridView1_RowEditing">
    <Columns>
        <asp:TemplateField HeaderText="Category">
            <ItemTemplate>
                <asp:Label ID="lblCategory" runat="server" Text='<%# Eval("Category") %>'></asp:Label>
            </ItemTemplate>
            <EditItemTemplate>
                <asp:DropDownList ID="ddlCategory" runat="server" DataSourceID="SqlDataSource1"
                    DataTextField="CategoryName" DataValueField="CategoryID" SelectedValue='<%# Bind("CategoryID") %>'>
                </asp:DropDownList>
            </EditItemTemplate>
        </asp:TemplateField>
        <asp:CommandField ShowEditButton="True" />
    </Columns>
</asp:GridView>

<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:YourConnectionString %>"
    SelectCommand="SELECT CategoryID, CategoryName FROM Categories"></asp:SqlDataSource>

protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
{
    GridView1.EditIndex = e.NewEditIndex;
    // 绑定数据源
    GridView1.DataSource = YourDataSource;
    GridView1.DataBind();
}