如何在 swift 4 中进行两个并发 API 调用

Question

提前感谢您的帮助， 我有两个 API 调用，都是并发的，任何调用都可能首先成功（我不想按顺序调用），在两个调用成功后，我必须停止我的活动指示器并重新加载我的 tableView， 这是我的代码，但我不知道这是否正确，以及如何重新加载我的 tableView 并停止我的活动指示器。

func downloadDetails(){
    let operationQueue: OperationQueue = OperationQueue()
    let operation1 = BlockOperation() {
    WebServiceManager.getAData(format:A, withCompletion: {(data: Any? , error: Error?) -> Void in

          if let success = data {
              DispatchQueue.main.async {
                  (success code)
              }
           }
        })

        let operation2 = BlockOperation() {
        webServiceManager.getBData(format: B, withCompletion: {(data: Any? , error: Error?) -> Void in

                if let success = data {
                    DispatchQueue.main.async {
                       (success code)
                    }
                }
            })
        }
        operationQueue.addOperation(operation2)
    }
    operationQueue.addOperation(operation1)
}
downloadDetails() "calling function"

Answer 1

我会使用 OperationQueue。

它是长时间运行的任务的首选，如果需要，您可以控制取消请求。

在每个操作结束时，您可以检查操作计数以了解剩余操作。

我添加了伪代码。

let operationQueue: OperationQueue = OperationQueue()

func downloadDetails(){

    let operation1 = BlockOperation() { [weak self] in

        guard let strongSelf = self else {
            return
        }

        sleep(2)

        DispatchQueue.main.async {
            strongSelf.handleResponse()
        }

        let operation2 = BlockOperation() { [weak self] in

            guard let strongSelf = self else {
                return
            }

            sleep(2)

            DispatchQueue.main.async {
                strongSelf.handleResponse()
            }
        }
        strongSelf.operationQueue.addOperation(operation2)
    }

    self.operationQueue.addOperation(operation1)
}

func handleResponse() {
    print("OPERATIONS IN PROGRESS: \(self.operationQueue.operations.count)")
    if self.operationQueue.operations.count == 0 {
        print("ALL OPERATIONS ARE COMPLETE")
    }
}

func cancelOperation() {
    self.operationQueue.cancelAllOperations()
}

打印出来

OPERATIONS IN PROGRESS: 1
OPERATIONS IN PROGRESS: 0
ALL OPERATIONS ARE COMPLETE

Answer 2

这正是DispatchGroup 的用例。为每个呼叫输入组，在呼叫结束时离开组，并添加一个通知处理程序以在它们全部完成时触发。不需要单独的操作队列；这些已经是异步操作了。

func downloadDetails(){
    let dispatchGroup = DispatchGroup()

    dispatchGroup.enter()   // <<---
    WebServiceManager.getAData(format:A, withCompletion: {(data: Any? , error: Error?) -> Void in

        if let success = data {

            DispatchQueue.main.async {
                (success code)
                dispatchGroup.leave()   // <<----
            }
        }
    })

    dispatchGroup.enter()   // <<---
    webServiceManager.getBData(format: B, withCompletion: {(data: Any? , error: Error?) -> Void in

        if let success = data {

            DispatchQueue.main.async {
               (success code)
               dispatchGroup.leave()   // <<----
            }
        }
    })

    dispatchGroup.notify(queue: .main) {
        // whatever you want to do when both are done
    }
}