title: asp:FileUpload has no file(flUploadDoc.HasFile = false) on first postback
body: <p>I have a asp:FileUpload in a user control it works well on second try but gives</p>
  
  <pre><code>flUploadDoc.HasFile = false '//Value in debug mode for first try.
  </code></pre>
  
  <p>The structure of page down to file upload is like</p>
  
  <p>master page --> page --> update panel(page) --> control --> update panel(control) --> file upload</p>
  
  <p>My control update panel code is like</p>
  
  <pre><code>&lt;asp:UpdatePanel ID="updPnlAttributes" runat="server"&gt;
      &lt;ContentTemplate&gt;
          :
          :
              &lt;div class="title"&gt;
                 Upload:
              &lt;/div&gt;
              &lt;div class="input-area"&gt;
                 &amp;nbsp;&lt;asp:FileUpload ID="flUploadDoc" runat="server" class="upload" /&gt;
              &lt;/div&gt;
          :
          :
      &lt;/ContentTemplate&gt;
      &lt;Triggers&gt;
          &lt;asp:PostBackTrigger ControlID="btnSavePropertyDocuments" /&gt;
      &lt;/Triggers&gt;
  &lt;/asp:UpdatePanel&gt;
  </code></pre>
  
  <p>I also tried to set a PostBackTrigger for the parent update panel.</p>
  
  <pre><code>Dim updPanelPropertyRecord As UpdatePanel = Parent.FindControl("updPanelPropertyRecord")
  Dim postBackTrigerBtnSave As PostBackTrigger = New PostBackTrigger
  postBackTrigerBtnSave.ControlID = btnSavePropertyDocuments.ClientID
  updPanelPropertyRecord.Triggers.Add(postBackTrigerBtnSave)
  updPanelPropertyRecord.Update()
  </code></pre>