why can't get $_FILES in my new tab for admin

[paul]

i develop a ADMIN tab for edit some new info , and it contain a image need to upload
in
public function displayForm() ,

i add ,

but when i submit the form

in public function postProcess(),

i can't get data from $_FILES ,

WHY ?
CAN SOMEONE TELL ME.
THANK YOU

[rocky]

Check to make sure you have instructed your form to send files. For example, use the following:

'<form action="'.$_SERVER['REQUEST_URI'].'" method="post" enctype="multipart/form-data">'

If your code is the following, then it won't send file information:

'<form action="'.$_SERVER['REQUEST_URI'].'" method="post">'