如何在asp.net中创建多选的SelectIndexChanged事件

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

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        // 绑定数据源
        ddlOptions.DataSource = GetOptions();
        ddlOptions.DataBind();
    }
}

protected void ddlOptions_SelectedIndexChanged(object sender, EventArgs e)
{
    // 处理选中项变化的逻辑
    foreach (ListItem item in ddlOptions.Items)
    {
        if (item.Selected)
        {
            // 处理选中项的值
            string selectedValue = item.Value;
            // 执行相应的操作
        }
    }
}