To all:

I am using the code below to design a "File Uploader" for my users.  All this works great.  The user starts with one file upload box and can add up to six more if desired.  The files get a GUID identifier appended to their names during upload.  After the upload, the File Upload Box count gets set back to one.

The problem is that after the files are uploaded and the File Upload Box is reset back to one, and is blank, if the user hits page refresh or reload, the same group of files that he just uploaded gets uploaded again.  Why?

How do I ensure the HttpFileCollection gets reset back to zero after the upload is complete?

Thank you.

Here's the code:   First the HTML then the code behind:

<div>
    <div>
    
    </div><br />
    <hr />
    <br />
    <table class="tableStyle" cellpadding="15" >
        <tr>
            <td>
                <div style="border-style: inset; border-width: 4px; width: 100%; height: 100%;" >
                    <br />
                    <asp:Label ID="lblFileUpload" runat="server" Text="Add File(s) To Be Uploaded: (MAX 6)" Font-Bold="true"></asp:Label><br />
                    <br />
                    <br />
                    <p id="upload-area" >
                        <input id="FileField" type="File" runat="server" size="45" />
                    </p>
                    <input id="ButtonAdd" type="button" value="Add File" onclick="addFileUploadBox()" class="buttonStyle" /><br />
                    <br />
                    <p align="right">
                        <asp:Button ID="btnUpload" runat="server" Text="Upload Now" OnClick="btnUpload_Click" CssClass="buttonStyle" />
                    </p>
                    <span id="Span1" style="color: Red" runat="server"></span>
                    <br />
                    <br />
                    <script type="text/javascript">
                        function addFileUploadBox() {
                            if (!document.getElementById || !document.createElement)
                                return false;


                            var uploadArea = document.getElementById("upload-area");
                            if (!uploadArea)
                                return;


//                            Limit user to 6 upload boxes maximum.
                            if (!addFileUploadBox.lastAssignedId || addFileUploadBox.lastAssignedId < 105)
                            {
                                var newLine = document.createElement("br");
                                uploadArea.appendChild(newLine);


                                var newUploadBox = document.createElement("input");
                                newUploadBox.type = "file";
                                newUploadBox.size = "45";
                                if (!addFileUploadBox.lastAssignedId)
                                    addFileUploadBox.lastAssignedId = 100;


                                newUploadBox.setAttribute("id", "FileField" + addFileUploadBox.lastAssignedId);
                                newUploadBox.setAttribute("name", "FileField" + addFileUploadBox.lastAssignedId);
                                uploadArea.appendChild(newUploadBox);
                                addFileUploadBox.lastAssignedId++;
                            }
                            else {
                                return false;
                            }


                        }
       
                    </script>
                </div>
</div>
</div>

Code Behind:

protected void btnUpload_Click(object sender, EventArgs e)
        {


            HttpFileCollection uploads = HttpContext.Current.Request.Files;
            for (int i = 0; i < uploads.Count; i++)
            {
                HttpPostedFile upload = uploads[i];


                if (upload.ContentLength == 0)
                    continue;

                string c = Guid.NewGuid().ToString() + Path.GetFileName(upload.FileName);
                try
                {
                    upload.SaveAs(Server.MapPath("~/" + "UserUploads/" + c));
                    Span1.InnerHtml = "Upload(s) successful.";
                }
                catch(Exception ex)
                {
                    Span1.InnerHtml = "Upload(s) FAILED. ERROR: " + ex.Message.ToString();                
                }

            }

Preventing duplicate form submission on refresh or when the user clicks the back button and manually submits the form a second time is one of the more difficult ASP.Net issues to solve. That is especially true in your case since a refresh (which pulls the page from the browser cache) will start the upload of the files all over again - before any code you might add to your server-side btnUpload click handler has a chance to stop it.

Probably the easiest solution (though far from fool proof as it does not prevent the user from hitting the back button then re-submitting) would be to do a Response.Redirect back to either the same page or to a new page ("Thank you for uploading, etc. . . . ") at the end of your btnUpload click handler. Here's the one to the same page:

Response.Redirect (Request.Url.ToString(), False)

Note that doing the above will retain any query string parameters but cause loss of any ViewState.

---

Bill, WESNet Designs
Team Lead - DotNetNuke Gallery Module Project (Not Actively Being Developed)
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