FileContentResult - prevent browser caching image

Question

I'm returning an image (png) from a call to an action method and I'd like to stop the image being cached by the browser.

return File(reply, "image/png", "{0}_Graph".FormatWith(ciName));

I've tried all the usual things, appending an array of different headers to the file output response and none of them seem to be working for me.

Basically my action method returns a graph that's generated on the server and could be different from moment to moment. I use Javascripts Image object on the client side and set its src to my action method.

var image = new Image();
image.src = baseUrl + params;

Each time the same URL is requested, the server is not hit.

I can append a random number etc to the querystring however I'm wondering if there's a better approach.

Answer 1

You can set appropriate HTTP headers to prevent caching (I do not know how to do this in ASP.NET, but I imagine it would be something like HTTP.Response.setHeader("foo", "bar"):

"Pragma-directive: no-cache"
"Cache-directive: no-cache"
"Cache-control: no-cache"
"Pragma: no-cache"
"Expires: 0"

or use the current timestamp if you don't like the random number solution:

image.src = baseUrl + params + '&t=' + new Date().getTime();