NSCache objectForKey: always return null after memory warning on iOS 8

I ran into an issue that only happened in iOS 8. I used NSCache

to store my images. After getting the memory warning, I get the images again and store them in the cache. However, after the warning, the cache cannot save my images. It always returns nil to me using objectForKey:

.
Here's part of my code:

 @interface ViewController ()
{
    NSCache *imageCache;
}

@implementation ViewController
- (instancetype)init
{
    self = [super init];
    if (self) {
        imageCache = [[NSCache alloc] init];
        [imageCache setTotalCostLimit:1024 * 1024 * 1];
    }
    return self;
}
- (void)imageDownloadManager:(ImageDownloadManager *)manager didReceiveImage:(UIImage *)image forObjectID:(NSString *)objecID
{   
    NSUInteger cost = [UIImageJPEGRepresentation(image, 0) length];
    image = [image smallImageWithCGSize:kImageThumbSize];
    [self.imageCache setObject:image forKey:objectID cost:cost];
    NSLog("image: %@",[self.imageCache objectForKey:objectID]);  //return nil
}
@end

      

        
        
        
      

    

Thank:)

SOLUTIONS

You must set countLimit

and the value must be greater than 0. Then you can use totalCostLimit

.