Martin Hollingsworth Martin Hollingsworth - 1 month ago 9
ASP.NET (C#) Question

Disabling browser caching for all browsers from ASP.NET

I'm after a definitive reference to what ASP.NET code is required to disabled browsers from caching the page. There are many ways to affect the HTTP headers and meta tags and I get the impression different settings are required to get different browsers to behave correctly. It would be really great to get a reference bit of code commented to indicate which works for all browsers and which is required for particular browser, including versions.

There is a huge amount of information about this issue there but I have yet to find a good reference that describes the benefits of each method and whether a particular technique has been superseded by a higher level API.

I'm particularly interested in ASP.NET 3.5 SP1 but it would be good to get answers for earlier version as well.

This blog entry Two Important Differences between Firefox and IE Caching describes some HTTP protocol behaviour differences.

The following sample code illustrates the kind of thing I am interested in

public abstract class NoCacheBasePage : System.Web.UI.Page
{
protected override void OnInit(EventArgs e)
{
base.OnInit(e);

DisableClientCaching();
}

private void DisableClientCaching()
{
// Do any of these result in META tags e.g. <META HTTP-EQUIV="Expire" CONTENT="-1">
// HTTP Headers or both?

// Does this only work for IE?
Response.Cache.SetCacheability(HttpCacheability.NoCache);

// Is this required for FireFox? Would be good to do this without magic strings.
// Won't it overwrite the previous setting
Response.Headers.Add("Cache-Control", "no-cache, no-store");

// Why is it necessary to explicitly call SetExpires. Presume it is still better than calling
// Response.Headers.Add( directly
Response.Cache.SetExpires(DateTime.UtcNow.AddYears(-1));
}
}

Answer

This is what we use in ASP.NET:

// Stop Caching in IE
Response.Cache.SetCacheability(System.Web.HttpCacheability.NoCache);

// Stop Caching in Firefox
Response.Cache.SetNoStore();

It stops caching in Firefox and IE, but we haven't tried other browsers. The following response headers are added by these statements:

Cache-Control: no-cache, no-store
Pragma: no-cache