ios多线程操作（十二）—— 自定义NSOperation实现网络下载后回调

#import <UIKit/UIKit.h>

@interface CXWebImageOperation : NSOperation
/**
 *  实例化web图片操作
 */
+ (instancetype)webImageOperationWithUrl:(NSString *)urlString completion:(void(^) (UIImage *image))completion;
@end

@interface CXWebImageOperation ()
/**
 *  图片的url
 */
@property (nonatomic,copy) NSString *urlString;
/**
 *  下载完图片后需要执行的代码块
 */
@property (nonatomic,copy) void (^completion)(UIImage *image);

@end

+ (instancetype)webImageOperationWithUrl:(NSString *)urlString completion:(void(^) (UIImage *image))completion
{
    CXWebImageOperation *op = [[self alloc] init];
    op.urlString = urlString;
    op.completion = completion;
    return op;
}

- (void)main
{
    @autoreleasepool {
        
        // 下载图片的耗时操作
        NSURL *url = [NSURL URLWithString:self.urlString];
        NSData *data = [NSData dataWithContentsOfURL:url];
        NSLog(@"已下载 %@",[NSThread currentThread]);
        UIImage *image = [UIImage imageWithData:data];
        
        // 主线程回调，完成操作后通知调用方完成回调
        dispatch_async(dispatch_get_main_queue(), ^{
            
            if (self.completion != nil) {
                self.completion(image);
                
            }
        });
    }
   
}

@interface ViewController ()
/**
 *  图片
 */
@property (weak, nonatomic) IBOutlet UIImageView *iconV;
/**
 *  操作队列
 */
@property (nonatomic,strong) NSOperationQueue *queue;
@end

- (NSOperationQueue *)queue
{
    if (_queue == nil) {
        _queue = [[NSOperationQueue alloc] init];
    }
    return _queue;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 图片下载操作
    CXWebImageOperation *op = [CXWebImageOperation webImageOperationWithUrl:@"http://p17.qhimg.com/dr/48_48_/t012d281e8ec8e27c06.png" completion:^(UIImage *image) {
     NSLog(@"%@",[NSThread currentThread]);
        // block回调在主线程更新UI
        self.iconV.image = image;
    }];
    // 添加进队列
    [self.queue addOperation:op];
}