ASP.NET - FileUpload with PostBack Trigger

Question

I have an UpdatePanel which has an upload control and a button to upload. The button is set as a trigger, but the event handler for the button fails to execute on the first PostBack.

My ASPX code is:

<asp:UpdatePanel ID="updPages" runat="server" UpdateMode="Conditional">
    <ContentTemplate>
        <div class="tabs">
            <ul>
                <li><asp:LinkButton ID="lnkContentsPages" runat="server" OnClick="updateContents" CommandArgument="pages">Pages</asp:LinkButton></li>
        <%-- these tabs change the ActiveViewIndex to show a different UserControl --%>
                <li><asp:LinkButton ID="lnkContentsImages" runat="server" OnClick="updateContents" CommandArgument="images">Images</asp:LinkButton></li>
            </ul>
            <div class="tabbedContent">
                <asp:MultiView runat="server" ID="mltContentsInner" ActiveViewIndex="0">
                    <asp:View ID="viwContentsImages" runat="server">
                        // ajax usercontrol for a list of images - works fine with ajax
                        <fieldset>
                            <legend>Upload New</legend>
                            <div class="formRow">
                                <asp:Label ID="lblFile" runat="server" Text="Filename" AssociatedControlID="uplFile" />
                                <asp:FileUpload ID="uplFile" runat="server" />
                            </div>
                            <div class="formRow">
                                <asp:Label ID="lblImageDescription" runat="server" Text="Description" AssociatedControlID="txtImageDescription" />
                                <asp:TextBox runat="server" ID="txtImageDescription" />
                            </div>
                            <asp:Button ID="btnUpload" runat="server" Text="Upload" CssClass="c3button btnUpload" CausesValidation="false" OnClick="btnUpload_Click" />
                        </fieldset>
                    </asp:View>
                    <asp:View ID="viwContentsPages" runat="server">
                        // ajax usercontrol - works fine with ajax
                    </asp:View>
                </asp:MultiView>
            </div>
        </div>
    </ContentTemplate>
    <Triggers>
        <asp:PostBackTrigger ControlID="btnUpload" />
    </Triggers>
</asp:UpdatePanel>

The button works without fail on the second and subsequent times, just not the first. Is there any reason for this?

Unfortunately not. Behavior seems intermittent, which is the worst type of bug. — Echilon
– Echilon, Commented May 14, 2010 at 13:04
I would strip this down to the bare bones. update panel and button and see if it fires, than start adding controls and code back one at a time to see what breaks. it. — jim
– jim, Commented May 26, 2010 at 15:36

anbalagan · Accepted Answer · 2013-01-16 08:19:43Z

3

need to add enctype="multipart/form-data" in the form tag of the page.

faced the same problem and the above work around made it upload the file in the first attempt. hope some one will find it useful.

answered Jan 16, 2013 at 8:19

anbalagan

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Comments

Jonathan · Accepted Answer · 2010-05-07 12:15:49Z

1

I dont know why this is happening. However you could attempt to add the event yourself by override the OnInit page cycle event in the aspx.cs file. Remember to remove the Click event from your HTML page.

protected override void OnInit(EventArgs e)
{

btnUpload.Click+= new EventHandler(btnUpload_Click);
base.OnInit(e);
}

Alternatively the Trigger might also need to be positioned directly below the UpdatePanel Tag

<asp:UpdatePanel ID="updPages" runat="server" UpdateMode="Conditional">  
 <Triggers> 
        <asp:PostBackTrigger ControlID="btnUpload" /> 
    </Triggers>

edited May 7, 2010 at 12:15

answered May 7, 2010 at 12:06

Jonathan

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Comments

Graham Clark · Accepted Answer · 2010-05-07 12:31:25Z

1

Maybe it's doing an AJAX postback the first time? On your UpdatePanel, try adding the attribute ChildrenAsTriggers="false".

This will stop any controls in the UpdatePanel causing asynchronous postbacks, so for every control that you want to cause a postback, you'll have to add an AsyncPostBackTrigger in the UpdatePanel's Triggers section.

answered May 7, 2010 at 12:31

Graham Clark

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1 Comment

Echilon Over a year ago

Not something I'd thought of but it had no effect.

Community · Accepted Answer · 2017-05-23 10:25:55Z

0

According to anbalagan's answer and an answer from another question, you should change the enctype property of the form element to 'multipart/form-data'. As it is said in this question's best answer, 'multipart/form-data' should be used whenever you write client-side code and need to post files to the server, e.g. use FileUpload controls.

I had the same problem as yours, changed the enctype of the form and now everything works fine.

edited May 23, 2017 at 10:25

CommunityBot

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answered Jan 20, 2014 at 8:07

Yulian

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