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iOS多线程NSOperation 之介绍

NSOperation是个抽象类，并不具备封装操作的能力，必须使用它的子类

使用NSOperation子类的方式有3种

1、NSInvocationOperation

2、NSBlockOperation

3、自定义子类继承NSOperation，实现内部相应的方法

注意：

默认情况下，NSInvocationOperation调用了start方法后并不会开一条新线程去执行操作，而是在当前线程同步执行操作

只有将NSOperation放到一个NSOperationQueue中，才会异步执行操作

一、队列的取消、暂停、恢复

1.取消队列的所有操作

- (void)cancelAllOperations;

提示：也可以调用NSOperation的- (void)cancel方法取消单个操作2.暂停和恢复队列

- (void)setSuspended:(BOOL)b; // YES代表暂停队列，NO代表恢复队列

- (BOOL)isSuspended;

二、操作优先级

设置NSOperation在queue中的优先级，可以改变操作的执行优先级

- (NSOperationQueuePriority)queuePriority;

- (void)setQueuePriority:(NSOperationQueuePriority)p;

优先级的取值

NSOperationQueuePriorityVeryLow = -8L, NSOperationQueuePriorityLow = -4L, NSOperationQueuePriorityNormal = 0, NSOperationQueuePriorityHigh = 4, NSOperationQueuePriorityVeryHigh = 8

三、操作依赖

NSOperation之间可以设置依赖来保证执行顺序

比如一定要让操作A执行完后，才能执行操作B，可以这么写

[operationB addDependency:operationA]; // 操作B依赖于操作A

可以在不同queue的NSOperation之间创建依赖关系

四、操作的监听

可以监听一个操作的执行完毕

- (void (^)(void))completionBlock; - (void)setCompletionBlock:(void (^)(void))block;

五、实例

1.NSInvocationOperation

//创建后调用start方法会在当前线程中同步执行任务，只有添加到OperationQueue中才有可能异步执行     NSInvocationOperation *opration=[[NSInvocationOperation alloc] initWithTarget:self selector:@selector(doSomething) object:nil];     [opration start];

执行结果：

2015-09-02 22:18:59.162 OpearationDemo1[1241:99390] {number = 1, name = main}

2.放在Queue中

//2.1 封装任务 NSInvocationOperation *opration1=[[NSInvocationOperation alloc] initWithTarget:self selector:@selector(doSomething) object:nil]; NSInvocationOperation *opration2=[[NSInvocationOperation alloc] initWithTarget:self selector:@selector(doSomething) object:nil];  NSInvocationOperation *opration3=[[NSInvocationOperation alloc] initWithTarget:self selector:@selector(doSomething) object:nil]; //2.2 创建队列 NSOperationQueue *queue=[[NSOperationQueue alloc] init]; queue.maxConcurrentOperationCount=2; //设置最大并发数 //设置依赖 [opration1 addDependency:opration2]; //2.3 添加到队列中 [queue addOperation:opration1]; [queue addOperation:opration2]; [queue addOperation:opration3];

执行结果：

2015-09-02 22:47:40.214 OpearationDemo1[1431:141437]

{number = 2, name = (null)}

2015-09-02 22:47:40.214 OpearationDemo1[1431:141436]

{number = 3, name = (null)}

2015-09-02 22:47:40.214 OpearationDemo1[1431:141437] {number = 2, name = (null)}

3. NSBlockOperation封装任务,

/*  NSBlockOperation具备开线程的能力，是否开线程决定于任务的个数  */ NSBlockOperation *opeation=[NSBlockOperation blockOperationWithBlock:^{  NSLog(@"%@  --->执行任务0",[NSThread currentThread]); }]; [opeation addExecutionBlock:^{  NSLog(@"%@  --->执行任务1",[NSThread currentThread]); }]; [opeation addExecutionBlock:^{  NSLog(@"%@  --->执行任务2",[NSThread currentThread]); }]; [opeation start];

运行结果：

2015-09-02 22:24:35.867 OpearationDemo1[1291:108447]

{number = 3, name = (null)} —>执行任务0

2015-09-02 22:24:35.867 OpearationDemo1[1291:108448]

{number = 2, name = (null)} —>执行任务2

2015-09-02 22:24:35.867 OpearationDemo1[1291:108357] {number = 1, name = main} —>执行任务1

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