WebKit: Forcing included files not to be cached

When I have a development "stumper", I first search around on CocoaBuilder and CocoaDev to see if anybody else has asked and answered the same question. Most of the time, I can find the answer there. Or I can try posting a question to the lists, or asking around of some developers I know. When all else fails, and I really need help, I use up one of the technical support incidents that comes with my Apple Developer Connection membership. These don't come cheap, so they are a last resort.

I've lately been doing some development with WebKit to display some HTML, and I've been looking for a way to prevent the display of a page from caching the files that it includes (images, stylesheets, javascript files, etc.). Normally caching is fine, but if I'm planning on changing the contents of a file that the page request includes and then reloading the page, the newly-changed file is ignored.

So I punted and asked Apple. And since it's a generic solution, maybe other developers can make use of this little tidbit. So I'm sharing it here.

Basically, the way that it works is by intercepting and modifying the request that's about to happen. You do this by setting the resource load delegate via setResourceLoadDelegate: and implementing webView: resource: willSendRequest: redirectResponse: fromDataSource:. Here's the salient chunk of code, directly from Apple.

-(NSURLRequest *)webView:(WebView *)sender
                resource:(id)identifier
         willSendRequest:(NSURLRequest *)request
        redirectResponse:(NSURLResponse *)redirectResponse
          fromDataSource:(WebDataSource *)dataSource
{
    // Update the status message
    [self updateResourceStatus];
    if ([request cachePolicy] != NSURLRequestReloadIgnoringCacheData)
    {
        NSLog(@"changing cache policy for %@", [request URL]);
        return [NSURLRequest requestWithURL:[request URL]
                                cachePolicy:NSURLRequestReloadIgnoringCacheData
                            timeoutInterval:[request timeoutInterval]];
    } else {
        return request;
    }
}

Share and enjoy!

Update: This method only works for pages loaded from a URL. If you load from an HTML string via -[WebFrame loadHTMLString:baseURL:] you're out of luck.