Question

An app I’m building needs to periodically check a known location for an updated file. It happens to be a PDF. If x amount of time has passed, the app needs to upload a new copy of the file. The following code snippet works. It downloads the file. But the app displays a cached version of the PDF instead of the new one. I confirmed this by looking in the app bundle. After this code runs, there is definitely a new file in the Documents directory. But in the bundle’s tmp/DiskImageCache-[random gibberish string] there is a copy of the old version of the PDF – and that is what is being displayed by my UIWebView.

I searched the NSFileManager docs and of course, schmoogled up a storm, but I have not been able to find a way to get the app to show the new upload instead of the cached version of the PDF.

Thanks a ton for any assistance you can render with this problem.

   -(void) checkFile:(NSString *)url andSaveTo:(NSString __autoreleasing *)filename {

    NSFileManager *manager = [NSFileManager defaultManager];
    NSError *error = nil;      
    NSDictionary *attributes = nil;

    if ([manager fileExistsAtPath:filename]) {

       attributes = [manager attributesOfItemAtPath:filename error:nil];

        double updateInterval = [[attributes fileCreationDate] timeIntervalSinceNow];
        cacheInterval = CacheInterval;

        if (ABS(updateInterval) > CacheInterval) {
         [self downloadFile:url andSaveTo:fileName];
        }
    }
}

Answer 1

you can always thwart caching by appending a random number to your url as a parameter

ex: address/yourfilehere.pdf?rand=0323094230948203984
and give your long random parameter a new randomly generated number each time