iOS 开发多线程 —— NSOperation

本文是根据文顶顶老师的博客学习而来，转载地址：http://www.cnblogs.com/wendingding/p/3809042.html

一、NSOperation简介

1.简单说明

NSOperation的作⽤：配合使用NSOperation和NSOperationQueue也能实现多线程编程

NSOperation和NSOperationQueue实现多线程的具体步骤：

（1）先将需要执行的操作封装到一个NSOperation对象中

（2）然后将NSOperation对象添加到NSOperationQueue中

（3）系统会⾃动将NSOperationQueue中的NSOperation取出来

（4）将取出的NSOperation封装的操作放到⼀条新线程中执⾏

2.NSOperation的子类

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

NSInvocationOperation:

示例代码：

- (void)viewDidLoad {
    [super viewDidLoad];

    NSInvocationOperation *operation = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(thread1) object:nil];
    [operation start];
    NSInvocationOperation *operation2 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(thread2) object:nil];
    [operation2 start];

}

-(void)thread1{
    NSLog(@"currentThread = %@",[NSThread currentThread]);
}

-(void)thread2{
   NSLog(@"currentThread2 = %@",[NSThread currentThread]);
}

 currentThread = <NSThread: 0x17406d780>{number = , name = main}

currentThread2 = <NSThread: 0x17406d780>{number = , name = main}

可以看见，并没有开启新的线程.

注意：操作对象默认在主线程中执行，只有添加到队列中才会开启新的线程。即默认情况下，如果操作没有放到队列中queue中，都是同步执行。只有将NSOperation放到一个NSOperationQueue中,才会异步执行操作

NSBlockOperation:

 NSBlockOperation *operation3 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"operation = %@",[NSThread currentThread]);
    }];
    [operation3 start];

看打印结果：
operation = <NSThread: 0x1700728c0>{number = , name = main}

注意：只要NSBlockOperation封装的操作数 > 1,就会异步执行操作

例如：

NSBlockOperation *operation3 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"operation = %@",[NSThread currentThread]);
    }];
    [operation3 addExecutionBlock:^{
        NSLog(@"operation2 = %@",[NSThread currentThread]);
    }];
    [operation3 start];

然后看打印结果：

operation = <NSThread: 0x1700706c0>{number = , name = main}
operation2 = <NSThread: 0x170075a40>{number = , name = (null)}

NSOperationQueue:

NSOperationQueue的作⽤：NSOperation可以调⽤start⽅法来执⾏任务,但默认是同步执行的

如果将NSOperation添加到NSOperationQueue(操作队列)中,系统会自动异步执行NSOperation中的操作

添加操作到NSOperationQueue中，自动执行操作，自动开启线程

示例：

- (void)viewDidLoad {
    [super viewDidLoad];

    NSInvocationOperation *operation1 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(thread1) object:nil];

    NSInvocationOperation *operation2 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(thread2) object:nil];

    NSBlockOperation *operation3 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"currentThread3 = %@",[NSThread currentThread]);
    }];

    [operation3 addExecutionBlock:^{
        NSLog(@"currentThread3_1 = %@",[NSThread currentThread]);
    }];

    NSOperationQueue *queue = [[NSOperationQueue alloc]init];
    //把操作添加到队列中
    //第一种方式
    [queue addOperation:operation1];
    [queue addOperation:operation2];
    [queue addOperation:operation3];
    //第二种方式
    [queue addOperationWithBlock:^{
        NSLog(@"currentThread4 = %@",[NSThread currentThread]);
    }];

}

-(void)thread1{
    NSLog(@"currentThread1 = %@",[NSThread currentThread]);
}

-(void)thread2{
   NSLog(@"currentThread2 = %@",[NSThread currentThread]);
}

查看结果：

currentThread1 = <NSThread: 0x17006f440>{number = , name = (null)}
currentThread2 = <NSThread: 0x17007d9c0>{number = , name = (null)}
currentThread3_1 = <NSThread: 0x17007d9c0>{number = , name = (null)}
currentThread3 = <NSThread: 0x17006f440>{number = , name = (null)}
currentThread4 = <NSThread: 0x17007d9c0>{number = , name = (null)}