How to show DropdownList in EditMode of GridView in ASP.Net C#？

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" OnRowEditing="GridView1_RowEditing" OnRowDataBound="GridView1_RowDataBound">
    <Columns>
        <asp:BoundField DataField="ID" HeaderText="ID" ReadOnly="True" />
        <asp:TemplateField HeaderText="Category">
            <ItemTemplate>
                <asp:Label ID="lblCategory" runat="server" Text='<%# Eval("Category") %>'></asp:Label>
            </ItemTemplate>
            <EditItemTemplate>
                <asp:DropDownList ID="ddlCategory" runat="server"></asp:DropDownList>
            </EditItemTemplate>
        </asp:TemplateField>
        <asp:CommandField ShowEditButton="True" />
    </Columns>
</asp:GridView>

protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
{
    GridView1.EditIndex = e.NewEditIndex;
    BindGridView();
}

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowState == DataControlRowState.Edit)
    {
        DropDownList ddlCategory = (DropDownList)e.Row.FindControl("ddlCategory");
        // 绑定下拉列表的数据源
        ddlCategory.DataSource = GetCategories();
        ddlCategory.DataTextField = "CategoryName";
        ddlCategory.DataValueField = "CategoryID";
        ddlCategory.DataBind();

        // 设置选中值
        DataRowView drv = (DataRowView)e.Row.DataItem;
        ddlCategory.SelectedValue = drv["CategoryID"].ToString();
    }
}

private DataTable GetCategories()
{
    // 获取下拉列表的数据源
    // 这里可以使用数据库查询或其他方式获取数据
    DataTable dt = new DataTable();
    dt.Columns.Add("CategoryID", typeof(int));
    dt.Columns.Add("CategoryName", typeof(string));
    dt.Rows.Add(1, "Category 1");
    dt.Rows.Add(2, "Category 2");
    dt.Rows.Add(3, "Category 3");
    return dt;
}