如何在asp.net中根据下拉列表的选择来绑定文本框？

<asp:DropDownList ID="ddlOptions" runat="server" AutoPostBack="True" OnSelectedIndexChanged="ddlOptions_SelectedIndexChanged">
    <asp:ListItem Text="选项1" Value="1"></asp:ListItem>
    <asp:ListItem Text="选项2" Value="2"></asp:ListItem>
    <asp:ListItem Text="选项3" Value="3"></asp:ListItem>
</asp:DropDownList>

<asp:TextBox ID="txtResult" runat="server"></asp:TextBox>

protected void ddlOptions_SelectedIndexChanged(object sender, EventArgs e)
{
    // 获取选中的值
    string selectedValue = ddlOptions.SelectedValue;

    // 根据选中的值进行逻辑处理
    switch (selectedValue)
    {
        case "1":
            txtResult.Text = "选中了选项1";
            break;
        case "2":
            txtResult.Text = "选中了选项2";
            break;
        case "3":
            txtResult.Text = "选中了选项3";
            break;
        default:
            txtResult.Text = "";
            break;
    }
}

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        // 设置下拉列表的初始值
        ddlOptions.SelectedIndex = 0;
    }
}