缓存处理（例如模糊或编辑）的图像

Question

Is there a best practice or library that helps cache processed images (ie images that have been created while the app is running) in iOS? I use SDWebImage for images that I download, but in various places in the app I blur or in other ways process some of these images. I would like to store the processed images in a cache so that I can access them easily rather than reprocess each time a user opens that image. What's the best way to do this?

Thanks!

Answer 1

The answer it seems is using NSCache. It's quite straightforward to do. I ended up with a subclass of NSCache to make sure memory warnings are handled.

Implementation of NATAutoPurgeCache (heavily based on other posts on StackOverflow)

@implementation NATAutoPurgeCache

+ (NATAutoPurgeCache *)sharedCache
{
    static NATAutoPurgeCache *_sharedCache = nil;

    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _sharedCache = [[self alloc] init];

    });

    return _sharedCache;
}

- (id)init
{
    self = [super init];
    if (self) {
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(removeAllObjects) name:UIApplicationDidReceiveMemoryWarningNotification object:nil];
    }
    return self;
}

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidReceiveMemoryWarningNotification object:nil];
}

@end

And using it when needed for an image: (in this case to store a blurred image)

            UIImage* blurImage = [myCache objectForKey:@"blurred placeholder image"];

            if (!blurImage)
            {
                dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
                UIImage* blurImage = self.activityPic.image;
                blurImage= [blurImage applyLightEffect];

                dispatch_async(dispatch_get_main_queue(), ^{
                    self.activityPic.image = blurImage;
                    });

                    [myCache setObject:blurImage forKey:@"blurred placeholder image"];
                });
            }
            else {
                self.activityPic.image = blurImage;
            }