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在iOS实际开发中,我们可能会遇到下面的场景:有以下四个操作A,B,C,D.要求A,B,C在子线程中执行,当A,B,C执行完毕之后回到主线程执行操作D,ABC之间可能会有相互依赖的关系,我们可以通过GCD和NSOperation都可以实现这样的需求.
1.GCD
// 用GCD - (void)useGCD { // 1.1可以创建一个全局并发队列,A,B,C操作会在子线程中并发执行,ABC不存在先后执行顺序 // dispatch_queue_t quque=dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); // 1.2也可以可以创建一个串行队列,A,B,C操作会在子线程中串行执行,A-B-C依次执行 dispatch_queue_t quque=dispatch_queue_create("com.hzsy.www", 0); // 2.创建一个队列组 dispatch_group_t group=dispatch_group_create(); // 3.进入队列组 dispatch_group_enter(group); // 4.向队列组中添加队列并异步执行 dispatch_group_async(group, quque, ^{ NSLog(@"A--begain-%@",[NSThread currentThread]); NSLog(@"A--end-%@",[NSThread currentThread]); }); dispatch_group_async(group, quque, ^{ NSLog(@"B--begain-%@",[NSThread currentThread]); NSLog(@"B--end-%@",[NSThread currentThread]); }); dispatch_group_async(group, quque, ^{ NSLog(@"C--begain-%@",[NSThread currentThread]); NSLog(@"C--end-%@",[NSThread currentThread]); }); // 5.当队列组中的操作执行结束后回到主线程执行操作D dispatch_group_notify(group, dispatch_get_main_queue(), ^{ NSLog(@"D--finished-%@",[NSThread currentThread]); }); // 6.离开队列组 dispatch_group_leave(group); /* 全局并发队列打印结果: 2016-05-22 21:36:58.518 GCD和NSOpration[797:144336] A--begain-<NSThread: 0x15c51f170>{number = 2, name = (null)} 2016-05-22 21:36:58.525 GCD和NSOpration[797:144335] B--begain-<NSThread: 0x15c556a90>{number = 3, name = (null)} 2016-05-22 21:36:58.525 GCD和NSOpration[797:144338] C--begain-<NSThread: 0x15c54ac90>{number = 4, name = (null)} 2016-05-22 21:36:58.525 GCD和NSOpration[797:144336] A--end-<NSThread: 0x15c51f170>{number = 2, name = (null)} 2016-05-22 21:36:58.525 GCD和NSOpration[797:144335] B--end-<NSThread: 0x15c556a90>{number = 3, name = (null)} 2016-05-22 21:36:58.525 GCD和NSOpration[797:144338] C--end-<NSThread: 0x15c54ac90>{number = 4, name = (null)} 2016-05-22 21:36:58.526 GCD和NSOpration[797:144001] D--finished-<NSThread: 0x15c50c380>{number = 1, name = main} */ /* 串行队列打印结果: 2016-05-22 21:39:20.660 GCD和NSOpration[805:145035] A--begain-<NSThread: 0x15c599cd0>{number = 2, name = (null)} 2016-05-22 21:39:20.670 GCD和NSOpration[805:145035] A--end-<NSThread: 0x15c599cd0>{number = 2, name = (null)} 2016-05-22 21:39:20.670 GCD和NSOpration[805:145035] B--begain-<NSThread: 0x15c599cd0>{number = 2, name = (null)} 2016-05-22 21:39:20.670 GCD和NSOpration[805:145035] B--end-<NSThread: 0x15c599cd0>{number = 2, name = (null)} 2016-05-22 21:39:20.671 GCD和NSOpration[805:145035] C--begain-<NSThread: 0x15c599cd0>{number = 2, name = (null)} 2016-05-22 21:39:20.671 GCD和NSOpration[805:145035] C--end-<NSThread: 0x15c599cd0>{number = 2, name = (null)} 2016-05-22 21:39:20.671 GCD和NSOpration[805:145012] D--finished-<NSThread: 0x15c604ba0>{number = 1, name = main} */ }
2.NSOperationQueue
1 @interface ViewController () 2 @property (nonatomic, strong) NSOperationQueue *queue; 3 @end 4 5 @implementation ViewController 6 7 - (void)viewDidLoad { 8 [super viewDidLoad]; 9 NSOperationQueue *queue= [[NSOperationQueue alloc]init]; 10 _queue=queue; 11 } 12 @end
// 用NSOperationQueue - (void)useOperationQueue { // 1.创建ABCD执行block void (^blockA)(void)=^(void){ NSLog(@"A--begain-%@",[NSThread currentThread]); NSLog(@"A--end-%@",[NSThread currentThread]); }; void (^blockB)(void)=^(void){ NSLog(@"B--begain-%@",[NSThread currentThread]); NSLog(@"B--end-%@",[NSThread currentThread]); }; void (^blockC)(void)=^(void){ NSLog(@"C--begain-%@",[NSThread currentThread]); NSLog(@"C--end-%@",[NSThread currentThread]); }; void (^blockD)(void)=^(void){ NSLog(@"D--finished-%@",[NSThread currentThread]); }; // 2.创建ABCD的NSBlockOperation操作block NSBlockOperation *opA=[NSBlockOperation blockOperationWithBlock:blockA]; NSBlockOperation *opB=[NSBlockOperation blockOperationWithBlock:blockB]; NSBlockOperation *opC=[NSBlockOperation blockOperationWithBlock:blockC]; NSBlockOperation *opD=[NSBlockOperation blockOperationWithBlock:blockD]; // 3.1设置D操作的依赖 [opD addDependency:opA]; [opD addDependency:opB]; [opD addDependency:opC]; // 3.2设置ABC之间的依赖,如果不设置的话ABC将并发执行 [opB addDependency:opA]; [opC addDependency:opB]; // 4.添加ABC操作到队列 [_queue addOperation:opA]; [_queue addOperation:opB]; [_queue addOperation:opC]; //5.添加D到主队列 [[NSOperationQueue mainQueue] addOperation:opD]; /* 设置ABC之间的依赖执行结果执行结果: 2016-05-22 21:55:29.114 GCD和NSOpration[828:148402] A--begain-<NSThread: 0x147556cc0>{number = 2, name = (null)} 2016-05-22 21:55:29.127 GCD和NSOpration[828:148402] A--end-<NSThread: 0x147556cc0>{number = 2, name = (null)} 2016-05-22 21:55:29.128 GCD和NSOpration[828:148402] B--begain-<NSThread: 0x147556cc0>{number = 2, name = (null)} 2016-05-22 21:55:29.128 GCD和NSOpration[828:148402] B--end-<NSThread: 0x147556cc0>{number = 2, name = (null)} 2016-05-22 21:55:29.130 GCD和NSOpration[828:148402] C--begain-<NSThread: 0x147556cc0>{number = 2, name = (null)} 2016-05-22 21:55:29.130 GCD和NSOpration[828:148402] C--end-<NSThread: 0x147556cc0>{number = 2, name = (null)} 2016-05-22 21:55:29.130 GCD和NSOpration[828:148377] D--finished-<NSThread: 0x14750c3e0>{number = 1, name = main} */ /* 不设置ABC之间的依赖执行结果: 2016-05-22 21:56:44.480 GCD和NSOpration[833:148926] A--begain-<NSThread: 0x1265a3730>{number = 2, name = (null)} 2016-05-22 21:56:44.480 GCD和NSOpration[833:148929] B--begain-<NSThread: 0x12658f4a0>{number = 3, name = (null)} 2016-05-22 21:56:44.480 GCD和NSOpration[833:148927] C--begain-<NSThread: 0x1265a2ea0>{number = 4, name = (null)} 2016-05-22 21:56:44.484 GCD和NSOpration[833:148926] A--end-<NSThread: 0x1265a3730>{number = 2, name = (null)} 2016-05-22 21:56:44.485 GCD和NSOpration[833:148929] B--end-<NSThread: 0x12658f4a0>{number = 3, name = (null)} 2016-05-22 21:56:44.485 GCD和NSOpration[833:148927] C--end-<NSThread: 0x1265a2ea0>{number = 4, name = (null)} 2016-05-22 21:56:44.485 GCD和NSOpration[833:148902] D--finished-<NSThread: 0x12650c3c0>{number = 1, name = main} */ }
从上面的打印结果可以看到ABC之间如果设置了依赖关系,只会创建一条子线程.如果不设置会创建多条子线程.
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原文地址：http://www.cnblogs.com/zhahao/p/5517986.html
