如何在 swift 4 中进行两个并发 API 调用

Question

预先感谢您的帮助， 我有两个 API 调用，都是并发的，任何调用都可以先成功（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，但我不知道这是正确的方法，也不知道如何重新加载我的 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

这正是

DispatchGroup

的用例。输入每个呼叫的组，在呼叫结束时离开组，并添加一个通知处理程序以在呼叫完成时触发。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
    }
}

Answer 2

我会使用OperationQueue。

它是长时间运行任务的首选，并让您可以根据需要控制取消请求。

在每个操作结束时，您可以检查操作计数以了解剩余的操作。

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()
}

此打印

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

Answer 3

在一种情况下，调度组可能会失败，假设第一个 api 响应在进入第二个组之前返回。因此，在这种情况下，您的通知块将在没有第二个 api 的情况下被调用。因此，为了防止出现该问题，您必须在任何 api 调用之前添加所有 Enter 语句。喜欢-

func download(){
    let dispatchGroup = DispatchGroup()
    /// Enter into the group for all the apis from here only.
    dispatchGroup.enter()  
    dispatchGroup.enter()   
    
    ApiManager.shared.data(request: firstRequest, withCompletion: {(data: Any? , error: Error?) -> Void in
        dispatchGroup.leave()  
    })

    ApiManager.shared.data(request: secondRequest, withCompletion: {(data: Any? , error: Error?) -> Void in
        dispatchGroup.leave() 
    })

    dispatchGroup.notify(queue: .main) {
        /// From here you may notify to hide indicator and reload the table.
    }
}