多个网络任务从0到9顺序执行,并且按顺序回调:

将所有操作顺序加入到队列中,执行操作.

将所有回调有序插入队列后执行;

@IBAction func clickAction(_ sender: Any) {        print("click \(Thread.current)")                /** 存放网络请求任务的队列 */        var requestList = Array
    
     .init()                /** 存放回调的队列 */        var cbList = Array
     
      .init(repeating: BlockOperation(block: {            print("default operation")        }), count: 10)                /** 记录网络请求有效回调的数量 */        var count = 0                for index in 0...9 {                        let operation = BlockOperation.init {                                print("request >> \(index) \(Thread.current)")                                var request = URLRequest.init(url: URL.init(string: "https://www.baidu.com")!)                request.timeoutInterval = 5                                let task = URLSession.shared.dataTask(with: request) { (data, response, error) in                                        //回调操作                    let op = BlockOperation.init(block: {                        print("callback -- \(index) -- \(Thread.current)")                    })                                        //将操作加入队列                    cbList[index] = op                    count += 1                                        //所有回调加入队列后,执行回调                    if count == 10 {                        self.doCallback(callbackList: cbList)                    }                }                                task.resume()            }                        //请求任务依次加入到队列中            requestList.append(operation)            if index > 0 {                let op1 = requestList[index-1]                let op2 = requestList[index]                op2.addDependency(op1) //使op2依赖op1            }                    }                //执行请求        let queue = OperationQueue.init()        queue.maxConcurrentOperationCount = -1        queue.addOperations(requestList, waitUntilFinished: false)            }        func doCallback(callbackList:Array
      
       ) -> Void {        let cbQueue = OperationQueue.init()        cbQueue.maxConcurrentOperationCount = 1 //设置为串行队列.(如果不需要顺序执行,可以设置为并行队列)        cbQueue.addOperations(callbackList, waitUntilFinished: true) //所有回调执行完成后,通知主线程,故设置true                OperationQueue.main.addOperation {            print("update UI \(Thread.current)")        }    }
      
     
    

输出结果

click 
    
     {number = 1, name = main}request >> 0 
     
      {number = 4, name = (null)}request >> 1 
      
       {number = 4, name = (null)}request >> 2 
       
        {number = 4, name = (null)}request >> 3 
        
         {number = 4, name = (null)}request >> 4 
         
          {number = 4, name = (null)}request >> 5 
          
           {number = 4, name = (null)}request >> 6 
           
            {number = 4, name = (null)}request >> 7 
            
             {number = 4, name = (null)}request >> 8 
             
              {number = 4, name = (null)}request >> 9 
              
               {number = 4, name = (null)}callback -- 0 -- 
               
                {number = 6, name = (null)}callback -- 1 -- 
                
                 {number = 7, name = (null)}callback -- 2 -- 
                 
                  {number = 7, name = (null)}callback -- 3 -- 
                  
                   {number = 7, name = (null)}callback -- 4 -- 
                   
                    {number = 7, name = (null)}callback -- 5 -- 
                    
                     {number = 7, name = (null)}callback -- 6 -- 
                     
                      {number = 6, name = (null)}callback -- 7 -- 
                      
                       {number = 6, name = (null)}callback -- 8 -- 
                       
                        {number = 7, name = (null)}callback -- 9 -- 
                        
                         {number = 7, name = (null)}update UI 
                         
                          {number = 1, name = main}