How to download image/pdf file from database using Gridview's linkbutton? - asp.net

Question

Here is my problem. I have a user control that will download a binary file (image, pdf etc.) using a link button in gridview.
<asp:GridView Visible="true" ID="GridView1" runat="server" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
RowStyle-BackColor="#A1DCF2" AlternatingRowStyle-BackColor="White" AlternatingRowStyle-ForeColor="#000"
AutoGenerateColumns="false">
<Columns>
<asp:BoundField DataField="ID" HeaderText="ID"/>
<asp:BoundField DataField="FileName" HeaderText="File Name"/>
<asp:TemplateField HeaderText="Action" ItemStyle-HorizontalAlign = "Center">
<ItemTemplate>
<asp:LinkButton ID="lnkDownload" runat="server" Text="Download" OnClick="DownloadFile" CommandArgument='<%# Eval("Id") %>'></asp:LinkButton>
<asp:LinkButton ID="lnkDelete" runat="server" Text="Delete" OnClick="DeleteFile" CommandArgument='<%# Eval("Id") %>'></asp:LinkButton>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
Code Behind:
Protected Sub DownloadFile(sender As Object, e As EventArgs)
Dim id As Integer = Integer.Parse(TryCast(sender, LinkButton).CommandArgument)
Dim bytes As Byte()
Dim fileName As String, contentType As String
Using con As New SqlConnection(DataSource.ConnectionString)
Using cmd As New SqlCommand()
cmd.CommandText = "select FileName, PatImage, FileType from DB where Id=#Id"
cmd.Parameters.AddWithValue("#Id", id)
cmd.Connection = con
con.Open()
Using sdr As SqlDataReader = cmd.ExecuteReader()
sdr.Read()
bytes = DirectCast(sdr("PatImage"), Byte())
contentType = sdr("FileType").ToString()
fileName = sdr("FileName").ToString()
End Using
con.Close()
End Using
End Using
Response.Clear()
Response.Buffer = True
Response.Charset = ""
Response.Cache.SetCacheability(HttpCacheability.NoCache)
Response.ContentType = contentType
Response.AppendHeader("Content-Disposition", "attachment; filename=" + fileName)
Response.BinaryWrite(bytes)
Response.Flush()
Response.End()
End Sub
But this is not working if I have an UpdatePanel in my parent aspx page. So i googled and I found an answer; that is to place a code in RowDataBound:
Private Sub GridView1_RowDataBound(sender As Object, e As GridViewRowEventArgs) Handles GridView1.RowDataBound
Dim lb As LinkButton = TryCast(e.Row.FindControl("lnkDownload"), LinkButton )
ScriptManager.GetCurrent(Me.Page).RegisterAsyncPostBackControl(lb)
End Sub
And a new error occurred. That is I can't find my linkButton inside my GridView using my code in my RowDataBound.
So i googled again, and i found out that i should add a property to my aspx page ClientIDMode="AutoID". But this is only working on framework 4.x. And I couldn't do that 'cause im currently using 3.5. Are there any remedies in my current situation?

Answer 1

A already found an answer, I just changed my RowDataBound content, refer to the code:
Private Sub GridView1_RowDataBound(sender As Object, e As GridViewRowEventArgs) Handles GridView1.RowDataBound
If e.Row.RowType = DataControlRowType.DataRow Then
Dim LButton = CType(e.Row.FindControl("lnkDownload"), System.Web.UI.WebControls.LinkButton)
Dim scriptManager__1 = ToolkitScriptManager.GetCurrent(Me.Page)
If scriptManager__1 IsNot Nothing Then
scriptManager__1.RegisterPostBackControl(LButton)
End If
End If
End Sub