php/png caching confusion

[Anon]

I've built an EIS system that generates bar charts on the fly and stores them as png files. My problem is, that the same page can create different charts by clicking on a different users name to view their reports. When you click on a different user to change the bar chart, the old one still shows, but if you hit refresh, it shows the new one.

The charts are being generated from session variables too.. so I don't know if it is a caching problem with the png file, or the session variables.

I've tried using this:

header("Cache-control: no-cache");
header("Expires: " . date("D, d M Y H:i:s") . " EST");

I dunno.. maybe its wrong.. but it doesn't seem to work.

Please help.
Thanks!

[crusty_php]

try this
yourURL.com?t=<?php echo (time());?>
this will create a unique url so the browser will always reload

[Anon]

I tried that.. didn't work. It's not the actual page that is getting cached, it's the png image that the browser is displaying. I'm considering forcing a refresh on the page, but would rather figure out how to make the png image not cache.

any ideas?

[Anon]

I ended up doing a automatic refresh on the page... so here's what I used

if (!$refreshed){
echo '<meta http-equiv="refresh" content="0">';
session_register("refreshed");
$refreshed = "yes";
} // refresh page
else{
//show the page
}

and on the page that switches views to the new chart, it clears out the session $refreshed variable, so when I get back to the chart page it refreshes again.. but only once

not a very pretty way of doing it.. but it works perfectly