Does NSURLConnection take advantage of NSURLCache?

Question

I\'m trying to figure out how to use the URL loading framework to load URLs taking advantage of caching.

I am using NSURLConnections and feeding them NSURLRequests.

Answer 1

Have you tried messing with the connection:willCacheResponse: method? According to the URL Loading System documentation, "By default the data for a connection is cached according to the support provided by the NSURLProtocol subclass that handles the request. An NSURLConnection Delegationdelegate can further refine that behavior by implementing connection:willCacheResponse:."

Answer 2

It will indeed use NSURLCache automatically, at least in some circumstances. Certainly it does in the following code:

EDIT - works in a OS X 10.6 Cocoa app, not iPhone (misread question)

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[]) {

    // run request with default cache policy
 NSMutableURLRequest *req=[NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http://en.wikipedia.org/"]];
 NSData *data=[NSURLConnection sendSynchronousRequest:req returningResponse:nil error:nil];
 NSLog(@"Received %d bytes", [data length]);

 sleep(10);

    // now run it asking it to use the cache
 [req setCachePolicy:NSURLRequestReturnCacheDataElseLoad];
 data=[NSURLConnection sendSynchronousRequest:req returningResponse:nil error:nil];
 NSLog(@"Received %d bytes", [data length]);

    return 0;
}

Answer 3

NOTE iOS 5 onwards provide a sharedURLCache that has both memory and disk capacity.

Nothing will cache unless you set the NSURLCache to have some capacity:

// A 10MB cache. This a good avatar-image-cache size but might be too 
// large for your app's memory requirements. YMMV.
[[NSURLCache sharedURLCache] setMemoryCapacity:1024*1024*10];

The default iPhone NSURLCache instance refuses to ever cache to disk. if you need this behaviour you must sub-class NSURLCache and implement your own disk cache. I have found numerous examples of disk caches on GitHub, though none of them do the entirely necessary "prune" step satisfactorily IMHO.