NSOperationQueue快速完成所有任务3

Question

我正在尝试实现NSOperationQueue完成swift 3中的所有任务操作.我创建了一个下面的演示代码,它正在按照我的期望工作.

func downloadTopStroiesDetails(){
    let operationQueue: OperationQueue = OperationQueue()
    let operation1 = BlockOperation() {
         print("BlockOperation1")
        for id in 0...5{
            operationQueue.addOperation(downloadArticle(index: id))
        }
        let operation2 = BlockOperation() {
            print("BlockOperation2")
        }
        operationQueue.addOperation(operation2)
    }
    operationQueue.addOperation(operation1)
}

func downloadArticle(index:Int) -> Operation {
    let operation: Operation = BlockOperation { () -> Void in
        print(index)
    }
    return operation
}
downloadTopStroiesDetails() // start calling 

输出:

BlockOperation1
0
1
2
3
4
5
BlockOperation2

但是当我在下载文章中使用Alamofire调用Web API时,方法输出是不同的.

func downloadArticle(index:Int) -> Operation {
        let operation = BlockOperation(block: {
            RequestManager.networkManager.fetchFromNetworkwithID(articleid: index) { (response:Any ,sucess:Bool) in
                if sucess{
                      print(index)
                    //let art = article.init(json:(response as? json)!)!
                    // self.saveDataIntoCoreData(data: art)
                    //self.all_TopArticle.append(art)
                }
            };
        })
        return operation
    }

现在输出:

BlockOperation1
BlockOperation2
0
1
2
3
4
5

我在这里做错了什么？

Answer 1

您的downloadArticle方法是创建一个立即完成的块操作,因为它反过来执行异步操作.

在异步提取完成之前,您需要阻止阻止到达目的地.使用信号量将是一种解决方案.

func downloadArticle(index:Int) -> Operation {
    let operation = BlockOperation(block: {
        let semaphore = DispatchSemaphore(value: 0)
        RequestManager.networkManager.fetchFromNetworkwithID(articleid: index) { (response:Any ,sucess:Bool) in
            if sucess{
                  print(index)
                //let art = article.init(json:(response as? json)!)!
                // self.saveDataIntoCoreData(data: art)
                //self.all_TopArticle.append(art)
            }
            semaphore.signal()
        };
        semaphore.wait()
    })
    return operation
}

使用此信号量可确保在网络提取完成之前,操作实际上不会完成.

您可能还希望将操作队列设置为串行而不是并发,以确保一次只允许一个操作运行.如果这是你想要的,那么将操作队列设置maxConcurrentOperationCount为1.