操作隊列（NSOperation）

操作隊列的幾種常用方法

1. NSInvocationOperation

-(void)invocationOperationWithQueue
{
    //01 創建一個非主隊列
    NSOperationQueue * queue = [[NSOperationQueue alloc]init];

    //02 封裝操作
    NSInvocationOperation *op1 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(download) object:nil];
    NSInvocationOperation *op2 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(download) object:nil];
    NSInvocationOperation *op3 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(download) object:nil];

    //03 添加操作到隊列中(內部會自動調用start方法)
    [queue addOperation:op1];
    [queue addOperation:op2];
    [queue addOperation:op3];
}

2. NSBlockOperation

-(void)blockOpertionQueue
{
   //01 創建隊列
   NSOperationQueue *queue = [[NSOperationQueue alloc]init];

   //02 封裝操作
   NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
       NSLog(@"1---%@",[NSThread currentThread]);
   }];

   NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
       NSLog(@"2---%@",[NSThread currentThread]);
   }];

   NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
       NSLog(@"3---%@",[NSThread currentThread]);
   }];

   //追加任務(系統自動開啟子線程來執行追加的任務)
   [op3 addExecutionBlock:^{
       NSLog(@"4+++++%@",[NSThread currentThread]);
   }];

   //03 添加操作到隊列中
   [queue addOperation:op1];
   [queue addOperation:op2];
   [queue addOperation:op3];

以上的Block方式還有一種簡便的實現方式：

 //1)創建操作 2)把操作添加到隊列
     NSOperationQueue * queue = [[NSOperationQueue alloc]init];

    [queue addOperationWithBlock:^{
        NSLog(@"5+++++%@",[NSThread currentThread]);
    }];

需要注意的是：這種實現方式雖然簡單，但是無法的到操作對象。

拓展：
操作隊列有一個屬性可以用來設置最大并發數，默認情況下，這個數為－1，表示同一時間可以執行的任務的數量不受限制：
static const NSInteger NSOperationQueueDefaultMaxConcurrentOperationCount = -1;
當然，我們可以手動修改這個屬性的值： queue.maxConcurrentOperationCount = 1;
如果修改成1的話，就表示同一時間只允許一個操作執行，也就是我們所說的串行，而在串行情況下，我們不可以給操作追加任務。

操作隊列中的依賴和監聽

-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    //01 創建隊列
    NSOperationQueue *queue = [[NSOperationQueue alloc]init];
    NSOperationQueue *queue2 = [[NSOperationQueue alloc]init];

    //02 3操作
    NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"1---%@",[NSThread currentThread]);
    }];

    NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"2---%@",[NSThread currentThread]);
    }];

    NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"3---%@",[NSThread currentThread]);
    }];

    NSBlockOperation *op4 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"4---%@",[NSThread currentThread]);
    }];

    NSBlockOperation *op5 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"5++++++++%@",[NSThread currentThread]);
    }];

    //設置監聽（在任務4執行完畢之后會立即來調用此方法）
    op4.completionBlock = ^{
        NSLog(@"任務執行完畢");
    };
     //設置依賴,通過設置依賴能控制操作的執行屬性，本程序的操作執行順序為：5-4-3-2-1
     //注意:不能設置循環依賴
     [op1 addDependency:op2];
     [op2 addDependency:op3];
     [op3 addDependency:op4];
     [op4 addDependency:op5];

     //03 添加操作到隊列
      [queue addOperation:op1];
      [queue addOperation:op2];
      [queue addOperation:op3];
      [queue addOperation:op4];
    //可以設置跨隊列依賴
     [queue2 addOperation:op5];

}

操作隊列線程間的通信

具體細節請看注釋，與前面的通信方式差別不大，代碼如下：

@implementation ViewController

-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    //創建非主操作隊列
    NSOperationQueue *queue=[[NSOperationQueue alloc]init];
    //封裝操作
    NSBlockOperation *op1=[NSBlockOperation blockOperationWithBlock:^{
        //獲得圖片的URL
        NSURL *url=[[NSURL alloc]initWithString:@"http://ww4.sinaimg.cn/bmiddle/695f1cd4jw1f5xetl00loj21y822t7wh.jpg"];
        //將圖片的二進制數據下載到本地
        NSData *data=[NSData dataWithContentsOfURL:url];
        //根據圖片的二進制數據生成一張圖片
        UIImage *image=[[UIImage alloc]initWithData:data];
        NSLog(@"%@",[NSThread currentThread]);
        //操作隊列線程間的通信方式
        [[NSOperationQueue mainQueue]addOperationWithBlock:^{
            self.imageV.image=image;
            NSLog(@"%@",[NSThread currentThread]);
        }];
    }];
    [queue addOperation:op1];

    //添加監聽
    [op1 addObserver:self forKeyPath:@"isFinished" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:NULL];
}
//監聽屬性的改變
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context{
    NSLog(@"%@",change[NSKeyValueChangeOldKey]);
    NSLog(@"%@",change[NSKeyValueChangeNewKey]);
}

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