iOS 開發多線程 —— NSOperation

本文是根據文頂頂老師的博客學習而來，轉載地址：http://www.cnblogs.com/wendingding/p/3809042.html

一、NSOperation簡介

1.簡單說明

NSOperation的作⽤：配合使用NSOperation和NSOperationQueue也能實現多線程編程

NSOperation和NSOperationQueue實現多線程的具體步驟：

（1）先將需要執行的操作封裝到一個NSOperation對象中

（2）然後將NSOperation對象添加到NSOperationQueue中

（3）系統會⾃動將NSOperationQueue中的NSOperation取出來

（4）將取出的NSOperation封裝的操作放到⼀條新線程中執⾏

 2.NSOperation的子類

NSOperation是個抽象類,並不具備封裝操作的能力,必須使⽤它的子類

使用NSOperation⼦類的方式有3種：

（1）NSInvocationOperation

（2）NSBlockOperation

（3）自定義子類繼承NSOperation,實現內部相應的⽅法

NSInvocationOperation:

示例代碼：

- (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 = 1, name = main}

currentThread2 = <NSThread: 0x17406d780>{number = 1, name = main}

可以看見，並沒有開啟新的線程.

註意：操作對象預設在主線程中執行，只有添加到隊列中才會開啟新的線程。即預設情況下，如果操作沒有放到隊列中queue中，都是同步執行。只有將NSOperation放到一個NSOperationQueue中,才會非同步執行操作 

NSBlockOperation:

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



看列印結果：
operation = <NSThread: 0x1700728c0>{number = 1, name = main}

註意：只要NSBlockOperation封裝的操作數 > 1,就會非同步執行操作

例如：

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


然後看列印結果：

operation = <NSThread: 0x1700706c0>{number = 1, name = main}
operation2 = <NSThread: 0x170075a40>{number = 4, name = (null)}

NSOperationQueue:

NSOperationQueue的作⽤：NSOperation可以調⽤start⽅法來執⾏任務,但預設是同步執行的

如果將NSOperation添加到NSOperationQueue(操作隊列)中,系統會自動非同步執行NSOperation中的操作

添加操作到NSOperationQueue中，自動執行操作，自動開啟線程

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];
    //把操作添加到隊列中
    //第一種方式
    [queue addOperation:operation1];
    [queue addOperation:operation2];
    [queue addOperation:operation3];
    //第二種方式
    [queue addOperationWithBlock:^{
        NSLog(@"currentThread4 = %@",[NSThread currentThread]);
    }];
    
}

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

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

查看結果：

currentThread1 = <NSThread: 0x17006f440>{number = 4, name = (null)}
currentThread2 = <NSThread: 0x17007d9c0>{number = 5, name = (null)}
currentThread3_1 = <NSThread: 0x17007d9c0>{number = 5, name = (null)}
currentThread3 = <NSThread: 0x17006f440>{number = 4, name = (null)}
currentThread4 = <NSThread: 0x17007d9c0>{number = 5, name = (null)}