#import <Foundation/Foundation.h>

HMDownloadOperation;

HMDownloadOperationDelegate <NSObject>

@optional

- (void)downloadOperation:(HMDownloadOperation *)operation didFinishDownload:(UIImage *)image;

HMDownloadOperation : NSOperation

@property (nonatomic, copy) NSString *imageUrl;

@property (nonatomic, strong) NSIndexPath *indexPath;

@property (nonatomic, weak) id<HMDownloadOperationDelegate> delegate;

@end

#import "HMDownloadOperation.h"

@implementation HMDownloadOperation

- (void)main

{

    @autoreleasepool {

        if (self.isCancelled) return;

        NSURL *url = [NSURL URLWithString:self.imageUrl];

        NSData *data = [NSData dataWithContentsOfURL:url]; // 下载

        UIImage *image = [UIImage imageWithData:data]; // NSData -> UIImage

        if (self.isCancelled) return;

        // 回到主线程

        [[NSOperationQueue mainQueue] addOperationWithBlock:^{

            if ([self.delegate respondsToSelector:@selector(downloadOperation:didFinishDownload:)]) {

                [self.delegate downloadOperation:self didFinishDownload:image];

            }

        }];

    }

}

@end