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How to prevent file uploading for some buttons.


I have a linkbutton to logout, when a file is selected with the .net file upload control and a click on the logout button, the upload is started. How to prevent it?


By default all buttons (that have submit behavior) causes postback on click. If file is selected in any <input type=”file” …/> of the form, this file is uploading to the server. This behavior doesn’t depend on whether the FileUploadProgress control exists in the page.

You can do the following trick: all buttons that should not cause the file uploading, should clear all inputs with type ‘file’.
Put the following code into your page:

<script type="text/JavaScript">
clearFileInputs() {

// get all inputs

var inp = document.getElementsByTagName("input");

for (var i = 0; i < inp.length; i++) {

var el = inp[i];

// input with type 'file' only and not empty

if (el.type == "file" && el.value != "") {

// clear it

if (document.all && !window.opera) {

el.parentNode.insertBefore(el.cloneNode(false), el);



else {

var new_span = document.createElement("SPAN");

el.parentNode.insertBefore(new_span, el);


new_span.innerHTML = new_span.innerHTML;

new_span.parentNode.insertBefore(new_span.firstChild, new_span);





return true;


The button that should not cause the files uploading:

<asp:LinkButton runat="server" OnClick="myHandle"
  OnClientClick="return clearFileInputs();" Text="Logout" />