动态创建的DropDownList在Postback上丢失ListItems

protected void Page_Load(object sender, EventArgs e)
{
    if (IsPostBack)
    {
        // 重新绑定数据和创建控件
    }
}

protected void Page_Load(object sender, EventArgs e)
{
    if (IsPostBack)
    {
        // 从ViewState或SessionState中恢复数据
        var listItems = (List<ListItem>)ViewState["listItems"];
        // 或者
        // var listItems = (List<ListItem>)Session["listItems"];

        // 重新绑定数据和创建控件
        DropDownList ddl = new DropDownList();
        ddl.ID = "myDropDownList";
        ddl.DataSource = listItems;
        ddl.DataBind();
    }
    else
    {
        // 初始化数据和创建控件
        var listItems = new List<ListItem>();
        // 添加数据
        listItems.Add(new ListItem("Item 1", "1"));
        listItems.Add(new ListItem("Item 2", "2"));
        listItems.Add(new ListItem("Item 3", "3"));

        // 保存数据到ViewState或SessionState
        ViewState["listItems"] = listItems;
        // 或者
        // Session["listItems"] = listItems;

        // 创建控件
        DropDownList ddl = new DropDownList();
        ddl.ID = "myDropDownList";
        ddl.DataSource = listItems;
        ddl.DataBind();
    }
}

protected void Page_Init(object sender, EventArgs e)
{
    // 重新创建控件
    DropDownList ddl = new DropDownList();
    ddl.ID = "myDropDownList";
    ddl.DataSource = listItems;
    ddl.DataBind();
}