HTML编辑器在回发后的代码中给出空值

Question

我在页面中有多个控件和HtmlEditor。

 <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Always">
    <Triggers>
        <asp:PostBackTrigger ControlID="SaveButton" />
    </Triggers>
    <ContentTemplate>
    <cc1:TabContainer CssClass="visoft__tab_xpie7" runat="server" ID="tab" ActiveTabIndex="0" Width="100%" Font-Size="11px">
     <cc1:TabPanel runat="server" HeaderText="اطلاعات پایه" ID="TabPanel1">
         <ContentTemplate>
          <div class="row">
           <span style="width: 100px" class="rowtitle">Category</span>
           <asp:DropDownList ID="CategoryDropDownList" runat="server" Width="200px" AutoPostBack="True" DataTextField="Name" DataValueField="ID" OnSelectedIndexChanged="CategoryDropDownList_SelectedIndexChanged" />
           <asp:RequiredFieldValidator ID="CategoryRFV" runat="server" ControlToValidate="CategoryDropDownList" ForeColor="Red" ValidationGroup="Save" ErrorMessage="مجموعه را انتخاب کنید." Text="*" />
          </div>

          <div class="row" style="height: 300px">
           <span style="width: 100px" class="rowtitle">توضیحات کامل</span>
           <editor:HtmlEditor Style="float: left" runat="server" Width="600px" ID="DescriptionHtmlEditor" />
           <asp:RequiredFieldValidator Text="*" ID="DescriptionRFV" runat="server" ControlToValidate="DescriptionHtmlEditor" ForeColor="Red" ValidationGroup="Save" ErrorMessage="توضیحات را وارد کنید ." />
           </div>
         </ContentTemplate>
        </cc1:TabPanel>
</cc1:TabContainer> 
 <div class="row" style="text-align: center">
   <asp:Button ID="SaveButton" class="button" Width="100px" OnClick="SaveButton_Click" runat="server" ValidationGroup="Save" Text="ذخیره" />
 </div>
 </ContentTemplate>
</asp:UpdatePanel>

所有控件都位于UpdatePanel内。

当我试图访问HTML编辑器时 在updatepanel的部分回发之后的text属性，它是空的。

  protected void OrderImageDropDownList_SelectedIndexChanged(object sender, EventArgs e)
{
     string description=  DescriptionHtmlEditor.Text;//value is empty.
 }