How to download a file from a content page inside UpdatePanel in ASP

Question

User-883001733 posted

I want to download a file from an ASP webforms page.

If I use a WebForm without a MasterPage everything is fine, I have a LinkButton with this:

    Private Sub linkDOWNLOAD_Click(sender As Object, e As EventArgs) Handles linkDOWNLOAD.Click
        Dim filePath = "C:\files\" + DropDownList1.SelectedItem.Value
        Dim fileStream As Stream = streamClient.someWebServiceReturningFileStream(filePath)
        Dim buffer(65536) As Byte
        Dim bytesRead = 0

        Response.BufferOutput = False
        HttpContext.Current.Response.Clear()
        HttpContext.Current.Response.ClearHeaders()
        HttpContext.Current.Response.ContentType = "application/octet-stream"
        HttpContext.Current.Response.AddHeader("Content-Disposition",
                    "attachment; filename=" + DropDownList1.SelectedItem.Value)

        bytesRead = fileStream.Read(buffer, 0, buffer.Length)

        While (bytesRead > 0)
            If (Response.IsClientConnected) Then
                Response.OutputStream.Write(buffer, 0, bytesRead)
                Response.Flush()
                buffer = New Byte(65536) {}
                bytesRead = fileStream.Read(buffer, 0, buffer.Length)
            Else
                bytesRead = -1
            End If
        End While

        Response.Flush()
        Response.Close()
        Response.End()
      End

As I said this works fine and the browser open the dialog to download the file, but if I try the same code in a button inside a content page within a MasterPage, then nothing happens.

The Master page has this inside:

...
<asp:UpdatePanel ID="updatePanelBODY" runat="server">
   <ContentTemplate>
        <asp:ContentPlaceHolder ID="contentBODY" runat="server">
        </asp:ContentPlaceHolder>                    
   </ContentTemplate>
</asp:UpdatePanel>
...

The Content page has this inside:

<asp:Content ID="Content2" ContentPlaceHolderID="contentBODY" runat="server">
    <asp:LinkButton ID="linkDOWNLOAD" runat="server">Download File</asp:LinkButton>
</asp:Content>

I don't know how to solve this and every example I have found is based on webforms without any master page.

Thanks for your help.

Answer 1

User-1330468790 posted

Hi Caserta83,

 

Caserta83

As I said this works fine and the browser open the dialog to download the file, but if I try the same code in a button inside a content page within a MasterPage, then nothing happens.

It would be a problem that the file is  the result of the partial page update since you used an UpdatePanel control. However, the UpdatePanel control is supposed to update contents and not a file download.

 

Caserta83

I don't know how to solve this and every example I have found is based on webforms without any master page.

The solution is to set the button to trigger a full page postback.

In your case, what you need to do is add below code in the "Page_Load" event handler.

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    ScriptManager.GetCurrent(Page).RegisterPostBackControl(linkDOWNLOAD)
End Sub

I reproduced your problem. After adding above code, you will find that a full page postback trigger (Press F12 in browser) and the file downloading works fine .

  

Hope this can help you.

Best regards,

Sean