File download from GridView rows in ASP.NET 4.0

• Inside columns tag, add one template field like below:

<asp:TemplateField HeaderText="Screen Shot">
    <ItemTemplate>
         <asp:Image ID="screenShot" runat="server" ImageUrl='<%# Eval("screenshot") %>' CssClass="image" AlternateText="No Screenshots available"/>
         <asp:LinkButton ID="lnkDownload" runat="server" CommandArgument='<%# Eval("screenshot") %>' CommandName="cmd">Download</asp:LinkButton>
   </ItemTemplate>
</asp:TemplateField>

• Add one OnRowCommand="GridView1_RowCommand" event inside

  <asp:GridView tag.

• Define the event "GridView1_RowCommand" as follows:

protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e) {
 
   if (e.CommandName == "cmd")
   {
      string filename = e.CommandArgument.ToString();
      if (filename != "")
      {
         string path = MapPath(filename);
         byte[] bts = System.IO.File.ReadAllBytes(path);
         Response.Clear();
         Response.ClearHeaders();
         Response.AddHeader("Content-Type", "Application/octet-stream");
         Response.AddHeader("Content-Length", bts.Length.ToString());
 
         Response.AddHeader("Content-Disposition", "attachment;   filename=" + filename);
 
         Response.BinaryWrite(bts);
 
         Response.Flush();
 
         Response.End();
      }
   } 
}

Important Points

• Example is given for Image download, but you can download files of any type by just giving the path in "CommandArgument" attribute
• Q: What is ImageUrl='' ???
• A: It is written to specify/evaluate the path of image that we got from dataset(column name in dataset is "screenshot").
• Q: What is CommandArgument='' ???
• A: Again CommandArgument takes the ImageUrl which is obtained from the dataset.