一、NSOperation的介紹

1、NSOperation的作用

配合使用NSOperation和NSOperationQueue實現多線程編程

2、實現多線程的具體步驟

1）將需要執行的操作封裝到一個NSOperation對象中

2）將NSOperation對象添加到NSOperationQueue中

3）系統自動將NSOperationQueue中的NSOperation取出來，並且將封裝的操作放到一條新線程中執行

3、NSOperation十個抽象類，並沒有封裝操作的能力，必須使用它的子類

4、子類的三種形式

1）NSInvocationOperation

2）NSBlockOpera

3）自定義繼承自NSOperation的子類，實現內部相應的方法

二、結合代碼

1、NSInvocationOperation的使用

1）沒有添加到隊列

- (void)useNSInvocationOperation
{
    //1.封裝操作
    NSInvocationOperation * operation1 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(invocationTask) object:nil];
    //開始執行
    [operation1 start];
    
    NSInvocationOperation * operation2 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(invocationTask2) object:nil];
    [operation2 start];
    
}
- (void)invocationTask
{
    NSLog(@"invocationTask,%@",[NSThread currentThread]);
}
- (void)invocationTask2
{
    NSLog(@"invocationTask2,%@",[NSThread currentThread]);
}

打印結果：

2016-03-14 17:53:59.638 NSoperation[3071:257804] invocationTask,<NSThread: 0x7f86fad06cb0>{number = 1, name = main}
2016-03-14 17:53:59.639 NSoperation[3071:257804] invocationTask2,<NSThread: 0x7f86fad06cb0>{number = 1, name = main}

 注意事項：結果中可以看出如果沒有放到隊列中，默認同步執行，都在主線程。

2）添加到隊列

 - (void)useNSInvocationOperation
 {
     //1.封裝操作
     NSInvocationOperation * operation1 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(invocationTask) object:nil];
    
     NSInvocationOperation * operation2 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(invocationTask2) object:nil];
     
     //2.創建隊列
     NSOperationQueue * queue = [[NSOperationQueue alloc]init];
     queue.maxConcurrentOperationCount = 2;//最大線程數：2-3最好
     
     //3.添加操作到隊列
     [queue addOperation:operation1];
     [queue addOperation:operation2];
     
 }
 - (void)invocationTask
 {
     NSLog(@"invocationTask,%@",[NSThread currentThread]);
 }
 - (void)invocationTask2
 {
     NSLog(@"invocationTask2,%@",[NSThread currentThread]);
 }

打印結果：

2016-03-14 17:57:33.192 NSoperation[3083:261277] invocationTask2,<NSThread: 0x7fd9b8f07ee0>{number = 2, name = (null)}
2016-03-14 17:57:33.192 NSoperation[3083:261278] invocationTask,<NSThread: 0x7fd9b8e13210>{number = 3, name = (null)}

 根據打印結果可以看出加入隊列之後，系統又開啟了兩條線程。

2、NSBlockOperation的使用

 //1.封裝操作
     NSBlockOperation * operation1 = [NSBlockOperation blockOperationWithBlock:^{
         NSLog(@"NSBlockOperation---operation1,%@",[NSThread currentThread]);
     }];
     //2.添加更多的操作
     [operation1 addExecutionBlock:^{
         NSLog(@"NSBlockOperation---%@",[NSThread currentThread]);
     }];
     
     [operation1 start];

輸出結果：

2016-03-14 18:04:22.577 NSoperation[3105:266124] NSBlockOperation---operation1,<NSThread: 0x7f9e7850a1c0>{number = 1, name = main}
2016-03-14 18:04:22.577 NSoperation[3105:266206] NSBlockOperation---<NSThread: 0x7f9e785a4eb0>{number = 2, name = (null)}

 注意事項：只要NSBlockOperation的封裝操作數大於1，就會執行一部操作

3、給線程添加依賴

 - (void)useNSInvocationOperation
 {
     //1.封裝操作
     NSInvocationOperation * operation1 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(invocationTask) object:nil];
    
     NSInvocationOperation * operation2 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(invocationTask2) object:nil];
     
      NSInvocationOperation * operation3 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(invocationTask3) object:nil];
     
     //2.創建隊列
     NSOperationQueue * queue = [[NSOperationQueue alloc]init];
     queue.maxConcurrentOperationCount = 3;//最大線程數：2-3最好
     
     //2.1設置依賴
     [operation1 addDependency:operation3];
     [operation3 addDependency:operation2];
     
     //3.添加操作到隊列
     [queue addOperation:operation1];
     [queue addOperation:operation2];
     [queue addOperation:operation3];
     
 }
 - (void)invocationTask
 {
     NSLog(@"invocationTask,%@",[NSThread currentThread]);
 }
 - (void)invocationTask2
 {
     NSLog(@"invocationTask2,%@",[NSThread currentThread]);
 }
 - (void)invocationTask3
 {
     NSLog(@"invocationTask3,%@",[NSThread currentThread]);
 }

輸出結果：

2016-03-14 18:12:21.066 NSoperation[3135:272293] invocationTask2,<NSThread: 0x7f845a54e500>{number = 2, name = (null)}
2016-03-14 18:12:21.067 NSoperation[3135:272293] invocationTask3,<NSThread: 0x7f845a54e500>{number = 2, name = (null)}
2016-03-14 18:12:21.067 NSoperation[3135:272293] invocationTask,<NSThread: 0x7f845a54e500>{number = 2, name = (null)}

 根據結果可以看出先執行的2又執行的3最後執行的1，並沒有根據添加到隊列的順序執行。

4、設置線程的優先級

1)operation1.queuePriority = NSOperationQueuePriorityHigh;

2)優先級的取值

NSOperationQueuePriorityVeryLow = -8L,

NSOperationQueuePriorityLow = -4L,

NSOperationQueuePriorityNormal = 0,

NSOperationQueuePriorityHigh = 4,

NSOperationQueuePriorityVeryHigh = 8