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Simple AJAX File Upload

By , 29 Dec 2006
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Introduction

AJAX is a great thing for ASP.NET developers. It has begun to level the playing field with rich client applications, in terms of user experience and responsiveness. One downside has been that many things that once worked are broken; including the FileUpload control.

The essence of the problem is that the FileUpload control does not work with asynchronous postbacks, and therefore does not work from within an AJAX UpdatePanel. The technique presented in this article allows the FileUpload control to work within an UpdatePanel, by forcing a full postback; however, the rest of the controls can still take advantage of the asynchronous postbacks provided by the UpdatePanel. The example application will be a simple web form containing a DatePicker Control, a Label and a FileUpload. We will see that the FileUpload will function via a full postback, but the DatePicker will retain its AJAX behaviour.

1. Create a New AJAX-enabled Web Project

When Microsoft AJAX is installed, it adds a new template to Visual Studio, ASP.NET AJAX-Enabled Web Site. Create a new one of these:

Create a new AJAX Web Site

2. Create a New Web Form

In this example, I have added an Eclipse Web Solutions ASP.NET DatePicker control, a Label, and a FileUpload control, all within an UpdatePanel:

Eclipse Web Solutions ASP.NET DatePicker

<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="conditional">
   <ContentTemplate>
      <ews:DatePicker ID="DatePicker1"
         runat="server" UsingUpdatePanel="True" /><br />
      <asp:Label ID="Label1" runat="server"></asp:Label><br /><br />
      <asp:FileUpload ID="FileUpload1" runat="server" />
      <asp:Button ID="Button1" runat="server"
         Text="Upload" />
   </ContentTemplate>
</asp:UpdatePanel>

Code-behind:

protected void DatePicker1_SelectionChanged(object sender, EventArgs e)
{
    Label1.Text = DatePicker1.DateValue.ToShortDateString();
}

protected void Button1_Click(object sender, EventArgs e)
{
    if (FileUpload1.HasFile)
    {
        Label1.Text = FileUpload1.FileName;
    }
}

It is at this point that we experience the problem. Run the form, and you will find that the file upload control does not work. Because the file upload control is within an UpdatePanel, the file is not posted to the server.

3. Enable File Upload Full Postback

As mentioned earlier, the trick is to force the file upload control to perform a full postback, and we do this using triggers. Triggers allow the developer to specify what will cause partial and full postbacks. They must be defined within the UpdatePanel but outside of the ContentTemplate. We want to create a trigger that will instruct the button that we are using for the upload to perform a full postback. The updated markup is:

<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="conditional">
 <Triggers>
  <asp:PostBackTrigger ControlID="Button1" />
 </Triggers>
 <ContentTemplate>
  <ews:DatePicker ID="DatePicker1" runat="server" UsingUpdatePanel="True" 
                  OnSelectionChanged="DatePicker1_SelectionChanged" /><br />
  <asp:Label ID="Label1" runat="server"></asp:Label><br /><br />
  <asp:FileUpload ID="FileUpload1" runat="server" />
  <asp:Button ID="Button1" runat="server" Text="Upload" OnClick="Button1_Click" />
 </ContentTemplate>
</asp:UpdatePanel>

Now, when the form is run, the DatePicker is still working asynchronously, but the file upload is also working, thanks to the PostBackTrigger.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

liammclennan
Web Developer
Australia Australia
Liam McLennan has been developing for the internet since 2001. He is passionate about delivering top quality I.T. solutions that address his customer's needs.

Comments and Discussions

 
AnswerRe: UpdateProgress Problem PinmemberThomas Maule2-Feb-10 5:44 
GeneralRe: UpdateProgress Problem PinmemberMember 353020313-Apr-11 20:52 
Generalproblem in file upload PinmemberShweta parikh19-Mar-09 22:53 
hi
 
in my application i m using a master page nd in page(which is using the master page)i m loading my ascx control.
 
in my ascx control i m using file upload control.
 
i have an update panel in my aspx page.
 
but when i debug my app i always get hasfile = false
 
i also tried to put another update panel in my ascx nd set triggers.
 
but now at this time when my control is loaded in aspx page i got an error a control with id btn2 could not be found.
 
i dont knw how to handle this.
 
can anyone help me?
 
thanx in advance.
 
shweta
GeneralMy vote of 1 Pinmemberdanny_pow23-Jan-09 0:12 
GeneralNeed Help.. Pinmemberji_vijay29-Oct-08 18:05 
GeneralRe: Need Help.. Pinmemberliammclennan29-Oct-08 18:07 
GeneralGreat Article PinmemberMember 446143322-Oct-08 2:27 
GeneralAlso important (at least UserControl) Pinmemberph8121-Oct-08 20:09 
GeneralRe: Also important (at least UserControl) Pinmembergezequiel0930-Oct-08 8:15 
GeneralRe: Also important (at least UserControl) Pinmembershogedal8-Feb-10 3:49 
QuestionSo,where is ajax here? Pinmemberab_dc11-Aug-08 3:39 
AnswerRe: So,where is ajax here? Pinmemberliammclennan11-Aug-08 11:15 
AnswerRe: So,where is ajax here? PinmemberPortatofe2-Oct-08 5:09 
AnswerRe: So,where is ajax here? PinmemberZinkyu30-Jan-09 10:22 
GeneralFile Upload PinmemberHendrikO17-Jun-08 1:12 
QuestionUpdate Panel Propblems. PinmemberHasan Mohiuddin Farooqi18-May-08 20:06 
QuestionWhat about a file upload control inside an ASCX user control inside an update panel Pinmemberfrankkirchner1-May-08 13:21 
AnswerRe: What about a file upload control inside an ASCX user control inside an update panel Pinmemberliammclennan1-May-08 13:41 
GeneralRe: What about a file upload control inside an ASCX user control inside an update panel Pinmemberfrankkirchner1-May-08 15:28 
AnswerSolution for using this technique with a user control Pinmemberkbomb98724-Jun-08 4:24 
GeneralRe: Solution for using this technique with a user control Pinmemberaikipoodle20-Jul-08 9:51 
GeneralRe: Solution for using this technique with a user control Pinmemberkaan057-Aug-09 10:10 
GeneralRe: Solution for using this technique with a user control Pinmemberprincerc14-Feb-09 3:26 
QuestionIs it possible to call upload from a menu item? Pinmemberalan9317-Mar-08 3:11 
AnswerRe: Is it possible to call upload from a menu item? Pinmemberliammclennan17-Mar-08 10:16 

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