iOS Memory issue (ARC) when downloading and saving large ammount of images from server

Question

The following code downloads 700+ images from a server with varying sizes, the issue here is that memory (even with ARC) is never released and eventually a memory warning appear

Answer 1

"dataWithContentsOfURL" returns an autoreleased NSData object and that doesn't normally get released until the end of the run loop or the end of the method, so it's no wonder you're filling up memory pretty quickly.

Change it to an explicit "initWithContentsOfURL" method and then force a release by doing "data = nil;" when you are absolutely done with the image data.

Answer 2

Based on your screenshot, I think the issue is with the NSURL caching rather than the actual NSData objects. Can you try the following:

In your Application Delegate, setup an initial URL cache:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Do initial setup
    int cacheSizeMemory = 16*1024*1024; // 16MB
    int cacheSizeDisk = 32*1024*1024; // 32MB
    NSURLCache *sharedCache = [[NSURLCache alloc] initWithMemoryCapacity:cacheSizeMemory diskCapacity:cacheSizeDisk diskPath:@"nsurlcache"];
    [NSURLCache setSharedURLCache:sharedCache];

    // Finish the rest of your didFinishLaunchingWithOptions and head into the app proper
}

Add the following to your Application Delegate:

- (void)applicationDidReceiveMemoryWarning:(UIApplication *)application {
    [[NSURLCache sharedURLCache] removeAllCachedResponses];
}

A cache file will be created:"Library/Caches/your_app_id/nsurlcache"

The link to the Apple example is here: URL Cache

Code not tested but this (or something similar) should sort your problem + plus you can experiment with the cache sizes.

Can you post another screenshot of Allocations in action with this code? I would expect to see memory use stop growing and flatten out.