Preserving input value of type="file" in ColdFusion on postback - coldfusion

Question

I have a form in ColdFusion that initially has 5 input fields for file uploading. Should the user realize they have more than 5 files to upload in the process of attaching them, I would like the form to preserve the values when it submits itself for the change in # of fields.
Using the <cfform> tag with the preservedata="yes" attribute is supposed to accomplish this - but all I'm getting is a temp value stored in the input's value on resubmit that isn't displayed in the field nor works for a submission.
edit: Thanks for the great answers everyone, you all helped and were correct. I was able to implement Adam's suggested solution. Works great! Thanks!
function changeFieldCount() // javascript function for submit on input count change
{
var count = document.forms[0].numtotal.options[document.forms[0].numtotal.selectedIndex].value;
document.forms[0].action = "me.cfm?count=" + count;
document.forms[0].submit();
}
<cfparam name="url.count" default="5">
<cfform name="dispfiles" method="post" enctype="multipart/form-data" preservedata="yes">
<!--- looping for file input fields --->
<cfloop index="counter" from="1" to="#url.count#">
<cfinput type="file" name="file#counter#" size="50" maxlength="60"><br>
</cfloop>
<br>Number of Files to Attach:
<!--- looping for # of input selection--->
<cfselect name="numtotal">
<cfloop index="cnt" from="1" to="20" step="1">
<cfoutput>
<option value="#cnt#" <cfif #cnt# eq #url.count#>selected</cfif>>
#cnt#
</option>
</cfoutput>
</cfloop>
</cfselect>
<cfinput type="button" name="op-display" value="Display" onclick="changeFieldCount()">
<cfinput type="button" name="op-upload" value="Attach Files" onclick="submitfrm(this.form)">
<cfinput type="button" name="cancel" value=" Cancel " onclick="window.close()">
</cfform>
This is what I'm getting when I view source on the resulting submission:
<input name="file1" id="file1" type="file" value=".../cfusion.war/neotmp8858718543274653167.tmp" maxlength="60" size="50" /><br>

Answer 1

This is by design in all browsers for security reasons. There is no way you can insert the value for a file field.

Answer 2

To elaborate on #SpliFF's answer, what you need to do is dynamically create more file fields with JavaScript.
Here's an example that uses jQuery to make the JavaScript a little easier. I've also used a variable to track the number of file fields displayed so that they all have a unique number appended to their names, making it possible to loop over and uniquely identify them server-side.
<script type="text/javascript"
src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script>
<script type="text/javascript">
//track the current number of file fields displayed
var numUploadFields = 5;
//attach an anonymous function to the button to add more fields
$(function(){
$("#add5").click(function(){
for (var i = 0; i < 5; i++){
numUploadFields += 1;
var newHTML = "<br/><input type='file' name='upload" +
numUploadFields + "' />";
$("#someSection").append(newHTML);
}
});
});
</script>
<form method="post" action="">
<div id="someSection">
<input type="file" name="upload1" /><br/>
<input type="file" name="upload2" /><br/>
<input type="file" name="upload3" /><br/>
<input type="file" name="upload4" /><br/>
<input type="file" name="upload5" />
</div>
<input type="button" id="add5" value="Add 5 more file fields" />
</form>

Answer 3

Build additional file inputs using JS DOM methods. Since you aren't leaving the page this is fast and nothing is lost.