• NSOperation

// 继承NSOperation
@interface MyNSoperation : NSOperation

@property (nonatomic, strong) UIImage *image;

@end

@implementation MyNSoperation

- (void)main {
    _image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"https://ws3.sinaimg.cn/large/006tKfTcgy1fjt9s573oxj30zk0qo0vp.jpg"]]];
}

@end

// 使用NSOperation
- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    _myImageView.image = nil;
    
    MyNSoperation *op = [[MyNSoperation alloc] init];
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    
    __weak typeof(op) waekOp = op;
    op.completionBlock = ^{
        UIImage *image = waekOp.image;
        dispatch_async(dispatch_get_main_queue(), ^{
            _myImageView.image = image;
        });
    };
    
    [queue addOperation:op];
}

• 现成的继承类

  • NSBlockOperation

  - (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
      _myImageView.image = nil;
    
      NSOperationQueue *queue = [[NSOperationQueue alloc] init];
  
      NSBlockOperation *op = [NSBlockOperation blockOperationWithBlock:^{
      UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"https://ws3.sinaimg.cn/large/006tKfTcgy1fjt9s573oxj30zk0qo0vp.jpg"]]];
      dispatch_async(dispatch_get_main_queue(), ^{
            self.myImageView.image = image;
        });
      }];
  
      [queue addOperation:op];
  }
  

  • NSInvocationOperation

  - (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
      _myImageView.image = nil;
    
      NSOperationQueue *queue = [[NSOperationQueue alloc] init];
      NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self   selector:@selector(downloadImage) object:nil];
      [queue addOperation:op];
  }
  
  - (void)downloadImage {
     UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"https://ws3.sinaimg.cn/large/006tKfTcgy1fjt9s573oxj30zk0qo0vp.jpg"]]];
      dispatch_async(dispatch_get_main_queue(), ^{
          _myImageView.image = image;
      });
  }
  

• 控制Queue最大并发数（为1时是串行Queue）

NSOperationQueue *queue = [[NSOperationQueue alloc] init];
queue.maxConcurrentOperationCount = 3;

• 获取主线程

[NSOperationQueue mainQueue];

• 读取当前Operation个数

[queue operationCount];

• cancel

  
  

cancel在队列中的Operation不会执行其中的main函数，直接调用complete。
cancel在线程中的Operation，该Operation被标记为isCancel，继续执行完其中的main函数，执行complete。
cancel还未加入队列中的Operation则直接变成cancel状态

• 等待队列完成后继续操作

[queue waitUntilAllOperationsAreFinished];

• 等待Operation完成

• 等待依赖的Operation完成 - Dependency

#import "FirstViewController.h"

@interface FirstViewController () {
    NSArray *_urls;
    NSOperationQueue *_downloadImageQueue;
    NSBlockOperation *_finalOperation;
}

@property (weak, nonatomic) IBOutlet UIImageView *imageView1;
@property (weak, nonatomic) IBOutlet UIImageView *imageView2;
@property (weak, nonatomic) IBOutlet UIImageView *imageView3;
@property (weak, nonatomic) IBOutlet UIImageView *indicateImageView;

@end

@implementation FirstViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    _urls = @[@"https://ws3.sinaimg.cn/large/006tKfTcgy1fjt9s573oxj30zk0qo0vp.jpg",
              @"https://ws3.sinaimg.cn/large/006tKfTcgy1fjtg0xmaptj30lz082q41.jpg",
              @"https://ws2.sinaimg.cn/large/006tKfTcgy1fjtise0maxj30ia0pljsm.jpg"];
    _downloadImageQueue = [[NSOperationQueue alloc] init];
    
    [self finishedDownload];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}

- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    NSArray *imageViews =@[_imageView1, _imageView2, _imageView3];
    [_downloadImageQueue setMaxConcurrentOperationCount:3];
    for (NSString *urlString in _urls) {
        NSBlockOperation *op = [NSBlockOperation blockOperationWithBlock:^{
            UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]]];
            dispatch_async(dispatch_get_main_queue(), ^{
                ((UIImageView *)[imageViews objectAtIndex:[_urls indexOfObject:urlString]]).image = image;
            });
        }];
        [_downloadImageQueue addOperation:op];
        [_finalOperation addDependency:op];
    }
    NSOperationQueue *finalQueue = [[NSOperationQueue alloc] init];
    [finalQueue addOperation:_finalOperation];
}

- (void)finishedDownload {
    _finalOperation = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"finished!");
        dispatch_async(dispatch_get_main_queue(), ^{
            [_indicateImageView setHidden:YES];
        });
    }];
}

@end

• 循环依赖

  
  

• 优先级

// 高优先级总在低优先级之前运行
typedef NS_ENUM(NSInteger, NSOperationQueuePriority) {
    NSOperationQueuePriorityVeryLow = -8L,
    NSOperationQueuePriorityLow = -4L,
    NSOperationQueuePriorityNormal = 0,
    NSOperationQueuePriorityHigh = 4,
    NSOperationQueuePriorityVeryHigh = 8
};

@property NSOperationQueuePriority queuePriority;

高优先级的Operation进入队列会挤占低优先级Operation的位置，但是不会挤占正在运行的Operation的位置