下拉值未在ViewState中保存

Question

我已将下拉列表值保存在db和viewstate中，但在页面加载时未加载。 有人可以告诉我我要去哪里了吗

protected void Page_Load(object sender, System.EventArgs e)
{
if (ViewState["ddSelectedValue"] != "0")
        {
            dd_RuleFor.SelectedValue = Convert.ToInt32(ViewState["ddSelectedValue"]).ToString();
        }
}

protected void btn_Save_Click(object sender, System.EventArgs e)
{
     if(chkRuleApprover.Checked == true && dd_RuleFor.SelectedValue != "0")
        {

            strSQL = "update UserFile  set Rule_Approval_Selection=" + dd_RuleFor.SelectedItem.Value  + " where UID=" + intUserID;
            objCmd = new System.Data.SqlClient.SqlCommand(strSQL, oconn);
            objCmd.ExecuteNonQuery();

            ViewState["ddSelectedValue"] = dd_RuleFor.SelectedValue.ToString();
        }
}

Answer 1

确保首先在页面加载时填充值，然后再使用以下条件填充值：

if(!Page.Ispostback())
{
if (ViewState["ddSelectedValue"] != "0")
    {
        dd_RuleFor.SelectedValue = Convert.ToInt32(ViewState["ddSelectedValue"]).ToString();
    }
}