NSURLConnection is returning old data

问题:

In my application, I am loading JSON data using the NSURLConnection method, what looks like this:

NSURLRequest *request = [[NSURLRequest alloc] initWithURL:
                                [NSURL URLWithString:@"theurl"]];
NSURLConnection *theConnection = [[NSURLConnection alloc] initWithRequest:request
                                                                 delegate:self];
[theConnection start];

I receive and save the data in the -didReceiveData: method, but if I update my JSON file on my server, the NSURLConnection still delivers me the old JSON, while the file is uploaded correctly to the server. Only if I delete the whole app from my iPhone (or iPhone Simulator) and rebuild the application, it receives the new Json file.

Does anyone know a solution for this problem?

回答1:

You'll need to tell the NSURLRequest to re-evaluate (if your server sends the appropriate modified headers) or not use it's cache. Here's a snippet from my JBAsyncImageView project (hint: Use NSURLRequestReloadRevalidatingCacheData or NSURLRequestReloadIgnoringLocalCacheData):

// Create request
self.imageRequest = [[NSURLRequest alloc] initWithURL:imageURL 
                                          cachePolicy:(self.cachesImage) ? NSURLRequestReturnCacheDataElseLoad : NSURLRequestReloadIgnoringLocalCacheData 
                                      timeoutInterval:self.downloadTimeoutInterval];

// Begin download
self.imageData = nil;
self.imageConnection = [[NSURLConnection alloc] initWithRequest:self.imageRequest 
                                                       delegate:self 
                                               startImmediately:YES];

回答2:

The easiest solution to prevent request caching is to add a timestamp parameter with current time at the end:

http://example.com/api.json?my=args&timestamp=2344992923