如何知道上次异步服务器调用何时结束

Question

我想知道在 for 循环中处理异步调用的最佳方法是什么，以便我们知道最后一次调用是何时进行/结束的。

这里的问题是 for 循环比服务器调用快，所以调用将被排队，我如何确保最后一个被制作并结束了？

举以下伪示例：

someData.forEach({(object) in 
    self.myFunc(object)
})
fileprivate func myFunc(object: object) {
    doesSomeServerAsyncCallWithObjectAndCompletion(object) {(success, desiredData) in 
        // HOW TO KNOW HERE THAT THIS WAS THE LAST CALL REQUESTED??
    }
}

Answer 1

使用 dispatchgroup

 let dispatchGroup = DispatchGroup()
 dispatchGroup.enter()
   longRunningFunction { dispatchGroup.leave() }
dispatchGroup.enter()
 longRunningFunctionTwo { dispatchGroup.leave() }
dispatchGroup.notify(queue: .main) {
  print("Both functions complete 👍")
}

例如

   let queue = DispatchQueue(label: "com.allaboutswift.dispatchgroup", attributes: .concurrent, target: .global())
    let group = DispatchGroup()
    group.enter()
    queue.async (group: group) {
        print("doing stuff again 1")
        group.leave()
    }
    group.enter()
    queue.async (group: group) {
        print("doing more stuff again 2 ")
        sleep(3)
        group.leave()
    }
    group.notify(queue: DispatchQueue.main) {
        print("done doing stuff again 3")
    }