Asp.Net如何从另一个dropdownlist填充dropdownlist

<asp:DropDownList ID="dropdownlist1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="dropdownlist1_SelectedIndexChanged"></asp:DropDownList>
<asp:DropDownList ID="dropdownlist2" runat="server"></asp:DropDownList>

protected void dropdownlist1_SelectedIndexChanged(object sender, EventArgs e)
{
    // 获取dropdownlist1的选中值
    string selectedValue = dropdownlist1.SelectedValue;

    // 根据选中值填充dropdownlist2
    if (selectedValue == "Value1")
    {
        dropdownlist2.Items.Clear();
        dropdownlist2.Items.Add(new ListItem("Option1", "1"));
        dropdownlist2.Items.Add(new ListItem("Option2", "2"));
        dropdownlist2.Items.Add(new ListItem("Option3", "3"));
    }
    else if (selectedValue == "Value2")
    {
        dropdownlist2.Items.Clear();
        dropdownlist2.Items.Add(new ListItem("Option4", "4"));
        dropdownlist2.Items.Add(new ListItem("Option5", "5"));
        dropdownlist2.Items.Add(new ListItem("Option6", "6"));
    }
    // 其他选中值的处理逻辑...
}