NSOperation添加操作依赖和监听

//创建队列

? ? NSOperationQueue *queue = [[NSOperationQueue alloc]init];

?? ?

? ? //封装操作

? ? NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{

? ? ? ? NSLog(@"1-----------%@",[NSThread currentThread]);

? ? }];

? ? NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{

? ? ? ? NSLog(@"2-----------%@",[NSThread currentThread]);

? ? }];

? ? NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{

? ? ? ? NSLog(@"3-----------%@",[NSThread currentThread]);

? ? }];

? ? NSBlockOperation *op4 = [NSBlockOperation blockOperationWithBlock:^{

? ? ? ? NSLog(@"4-----------%@",[NSThread currentThread]);

? ? }];

?

　　　op3.completionBlock = ^{//添加监听，操作执行完毕后 回调

? ? ? ? NSLog(@"op3执行完毕。。");

? ? };

?? ?

? ? //添加操作依赖? 4->3->2->1? ? // 添加操作依赖能控制多任务并发的执行顺序，不能设置循环依赖,可以跨队列添加依赖

? ? [op3 addDependency:op4];

? ? [op2 addDependency:op3];

? ? [op1 addDependency:op2];

?? ?

? ? //添加到队列中

? ? [queue addOperation:op1];

? ? [queue addOperation:op2];

? ? [queue addOperation:op3];

? ? [queue addOperation:op4];

?

执行结果：

2019-02-22 23:59:43.749883+0800 下载图片[15917:488100] 4-----------<NSThread: 0x600000e28100>{number = 3,name = (null)}

2019-02-22 23:59:43.750367+0800 下载图片[15917:488101] 3-----------<NSThread: 0x600000e34000>{number = 4,name = (null)}

2019-02-22 23:59:43.750513+0800 下载图片[15917:488100] 2-----------<NSThread: 0x600000e28100>{number = 3,name = (null)}

2019-02-22 23:59:43.750654+0800 下载图片[15917:488100] 1-----------<NSThread: 0x600000e28100>{number = 3,name = (null)}