套话

与GCD一样，NSOperation也是我们日常开发中经常用到的多线程技术。本文将会介绍NSOperation的基本使用、添加依赖、

初次使用

NSOperation是个抽象类，依赖于子类NSInvocationOperation、NSBlockOperation去实现

下面是开发者文档上对NSOperation的一段描述请添加图片描述

NSInvocationOperation

基本使用

- (void)test {// 处理事务NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:selfselector:@selector(handleInvocation:) object:@"Felix"];// 创建队列NSOperationQueue *queue = [[NSOperationQueue alloc] init];// 操作加入队列[queue addOperation:op];
}- (void)handleInvocation:(id)operation {NSLog(@"%@ --- %@",operation, [NSThread currentThread]);
}
--------------------输出结果：-------------------
Felix --- <NSThread: 0x6000000422c0>{number = 3, name = (null)}
--------------------输出结果：-------------------

直接处理事务，不添加隐性队列

- (void)test {NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(handleInvocation:) object:@"Felix"];[op start];
}

- (void)test {NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(handleInvocation:) object:@"Felix"];NSOperationQueue *queue = [[NSOperationQueue alloc] init];[queue addOperation:op];[op start];
}

请添加图片描述

上述代码之所以会崩溃，是因为线程生命周期：

queue addOperation:op已经将处理事务的操作任务加入到队列中，并让线程运行
op start将已经运行的线程再次运行会造成线程混乱

NSBlockOperation

NSInvocationOperation和NSBlockOperation两者的区别在于：

前者类似target形式
后者类似block形式——函数式编程，业务逻辑代码可读性更高

- (void)test {// 初始化添加事务NSBlockOperation *bo = [NSBlockOperation blockOperationWithBlock:^{NSLog(@"任务1————%@",[NSThread currentThread]);}];// 添加事务[bo addExecutionBlock:^{NSLog(@"任务2————%@",[NSThread currentThread]);}];// 回调监听bo.completionBlock = ^{NSLog(@"完成了!!!");};NSOperationQueue *queue = [[NSOperationQueue alloc] init];[queue addOperation:bo];NSLog(@"事务添加进了NSOperationQueue");
}--------------------输出结果：-------------------
事务添加进了NSOperationQueue
任务1————<NSThread: 0x6000032dc1c0>{number = 5, name = (null)}
任务2————<NSThread: 0x6000032a1880>{number = 4, name = (null)}
完成了!!!
--------------------输出结果：-------------------

NSOperationQueue是异步执行的，所以任务一、任务二的完成顺序不确定

执行顺序

下列代码可以证明操作与队列的执行效果是异步并发的

- (void)test {NSOperationQueue *queue = [[NSOperationQueue alloc] init];for (int i = 0; i < 5; i++) {[queue addOperationWithBlock:^{NSLog(@"%@---%d", [NSThread currentThread], i);}];}
}
--------------------输出结果：-------------------
<NSThread: 0x600002771600>{number = 3, name = (null)}---0
<NSThread: 0x60000277ac80>{number = 7, name = (null)}---3
<NSThread: 0x600002774840>{number = 6, name = (null)}---2
<NSThread: 0x600002776a80>{number = 8, name = (null)}---4
<NSThread: 0x60000270c540>{number = 5, name = (null)}---1
--------------------输出结果：-------------------

设置优先级

NSOperation设置优先级只会让CPU有更高的几率调用，不是说设置高就一定全部先完成

不使用sleep——高优先级的任务一先于低优先级的任务二

- (void)test {NSBlockOperation *bo1 = [NSBlockOperation blockOperationWithBlock:^{for (int i = 0; i < 5; i++) {//sleep(1);NSLog(@"第一个操作 %d --- %@", i, [NSThread currentThread]);}}];// 设置最高优先级bo1.qualityOfService = NSQualityOfServiceUserInteractive;NSBlockOperation *bo2 = [NSBlockOperation blockOperationWithBlock:^{for (int i = 0; i < 5; i++) {NSLog(@"第二个操作 %d --- %@", i, [NSThread currentThread]);}}];// 设置最低优先级bo2.qualityOfService = NSQualityOfServiceBackground;NSOperationQueue *queue = [[NSOperationQueue alloc] init];[queue addOperation:bo1];[queue addOperation:bo2];
}--------------------输出结果：-------------------
第一个操作 0 --- <NSThread: 0x600002254280>{number = 6, name = (null)}
第一个操作 1 --- <NSThread: 0x600002254280>{number = 6, name = (null)}
第一个操作 2 --- <NSThread: 0x600002254280>{number = 6, name = (null)}
第一个操作 3 --- <NSThread: 0x600002254280>{number = 6, name = (null)}
第一个操作 4 --- <NSThread: 0x600002254280>{number = 6, name = (null)}
第二个操作 0 --- <NSThread: 0x600002240340>{number = 7, name = (null)}
第二个操作 1 --- <NSThread: 0x600002240340>{number = 7, name = (null)}
第二个操作 2 --- <NSThread: 0x600002240340>{number = 7, name = (null)}
第二个操作 3 --- <NSThread: 0x600002240340>{number = 7, name = (null)}
第二个操作 4 --- <NSThread: 0x600002240340>{number = 7, name = (null)}
--------------------输出结果：-------------------

使用sleep进行延时——高优先级的任务一慢于低优先级的任务二

第二个操作 0 --- <NSThread: 0x600002b35840>{number = 7, name = (null)}
第二个操作 1 --- <NSThread: 0x600002b35840>{number = 7, name = (null)}
第二个操作 2 --- <NSThread: 0x600002b35840>{number = 7, name = (null)}
第二个操作 3 --- <NSThread: 0x600002b35840>{number = 7, name = (null)}
第二个操作 4 --- <NSThread: 0x600002b35840>{number = 7, name = (null)}
第一个操作 0 --- <NSThread: 0x600002b3c700>{number = 5, name = (null)}
第一个操作 1 --- <NSThread: 0x600002b3c700>{number = 5, name = (null)}
第一个操作 2 --- <NSThread: 0x600002b3c700>{number = 5, name = (null)}
第一个操作 3 --- <NSThread: 0x600002b3c700>{number = 5, name = (null)}
第一个操作 4 --- <NSThread: 0x600002b3c700>{number = 5, name = (null)}

线程间通讯

在GCD中使用异步进行网络请求，然后回到主线程刷新UI
NSOperation中也有类似在线程间通讯的操作

- (void)test {NSOperationQueue *queue = [[NSOperationQueue alloc] init];queue.name = @"Felix";[queue addOperationWithBlock:^{NSLog(@"请求网络%@--%@", [NSOperationQueue currentQueue], [NSThread currentThread]);[[NSOperationQueue mainQueue] addOperationWithBlock:^{NSLog(@"刷新UI%@--%@", [NSOperationQueue currentQueue], [NSThread currentThread]);}];}];
}
--------------------输出结果：-------------------
请求网络<NSOperationQueue: 0x7ff4a240bae0>{name = 'Felix'}--<NSThread: 0x6000007dcf00>{number = 5, name = (null)}
刷新UI<NSOperationQueue: 0x7ff4a24087d0>{name = 'NSOperationQueue Main Queue'}--<NSThread: 0x60000078c8c0>{number = 1, name = main}
--------------------输出结果：-------------------

设置并发数

在GCD中只能使用信号量来设置并发数
而NSOperation轻易就能设置并发数
- 通过设置maxConcurrentOperationCount来控制单次出队列去执行的任务数

- (void)test {NSOperationQueue *queue = [[NSOperationQueue alloc] init];queue.name = @"Felix";queue.maxConcurrentOperationCount = 2;for (int i = 0; i < 5; i++) {[queue addOperationWithBlock:^{ // 一个任务[NSThread sleepForTimeInterval:2];NSLog(@"%d-%@",i,[NSThread currentThread]);}];}
}
--------------------输出结果：-------------------
1-<NSThread: 0x6000009290c0>{number = 5, name = (null)}
0-<NSThread: 0x6000009348c0>{number = 8, name = (null)}
3-<NSThread: 0x6000009290c0>{number = 5, name = (null)}
2-<NSThread: 0x60000094b0c0>{number = 7, name = (null)}
4-<NSThread: 0x6000009348c0>{number = 8, name = (null)}
--------------------输出结果：-------------------

添加依赖

在NSOperation中添加依赖能很好的控制任务执行的先后顺序

- (void)test {NSOperationQueue *queue = [[NSOperationQueue alloc] init];NSBlockOperation *bo1 = [NSBlockOperation blockOperationWithBlock:^{[NSThread sleepForTimeInterval:0.5];NSLog(@"请求token");}];NSBlockOperation *bo2 = [NSBlockOperation blockOperationWithBlock:^{[NSThread sleepForTimeInterval:0.5];NSLog(@"拿着token,请求数据1");}];NSBlockOperation *bo3 = [NSBlockOperation blockOperationWithBlock:^{[NSThread sleepForTimeInterval:0.5];NSLog(@"拿着数据1,请求数据2");}];//添加依赖[bo2 addDependency:bo1];[bo3 addDependency:bo2];[queue addOperations:@[bo1,bo2,bo3] waitUntilFinished:YES];NSLog(@"执行完了?我要干其他事");
}--------------------输出结果：-------------------
请求token
拿着token,请求数据1
拿着数据1,请求数据2
执行完了?我要干其他事
--------------------输出结果：-------------------

注意不要添加依赖导致循环运用，会导致依赖无效并会在控制台打印出"XPC connection interrupted" 请添加图片描述

任务的挂起、继续、取消

// 挂起
queue.suspended = YES;
// 继续
queue.suspended = NO;
// 取消
[queue cancelAllOperations];

请添加图片描述
这幅图是并发量为2的情况：

挂起前：任务3、任务4等待被调度
挂起瞬间：任务3、任务4已经被调度出队列，准备执行，此时它们是无法挂起的
挂起后：任务3、任务4被线程执行，而原来的队列被挂起不能被调度

自定义NSOperation缓存机制

NSOperation异步处理

NSOperationQueue *queue = [[NSOperationQueue alloc] init];UIImageView *imageView = [[UIImageView alloc] init];imageView.frame = CGRectMake(100, 100, 100, 100);[self.view addSubview:imageView];NSString *urlStr = [NSString stringWithFormat:@"https://profile-avatar.csdnimg.cn/910a183044d54231b5e418c23a558516_weixin_61196797.jpg!1"];NSURL *imageURL = [NSURL URLWithString:urlStr];NSBlockOperation *bo = [NSBlockOperation blockOperationWithBlock:^{NSLog(@"去下载图片" );// 延迟NSData *data   = [NSData dataWithContentsOfURL:imageURL];UIImage *image = [UIImage imageWithData:data];// 更新UI[[NSOperationQueue mainQueue] addOperationWithBlock:^{imageView.image = image;NSLog(@"加载完成");imageView.backgroundColor = [UIColor redColor];}];}];[queue addOperation:bo];