如何使用Swift在iOS上使用异步操作同步运行两个函数 [英] How to run synchronically two functions with async operations on iOS using Swift

问题描述

让我们提出这个场景

一个使用异步网络操作的方法

a method with async network operations

func asyncMethodA() -> String?
{
   result : String?
   Alamofire.manager.request(.POST, "https://www.apiweb.com/apimethod", parameters: parameters, encoding:.JSON)
            .response { (request, response, rawdata, error) in
                if (response?.statusCode == 200)
                {
                    //DO SOME HEAVY LIFTING
                }
        }
        return result //string

}

使用异步网络操作的另一种方法

another method with async network operations

func asyncMethodB() -> String?
{
   result : String?
   Alamofire.manager.request(.POST, "https://www.yetanotherapiweb.com/apimethod", parameters: parameters, encoding:.JSON)
            .response { (request, response, rawdata, error) in
                if (response?.statusCode == 200)
                {
                    //DO SOME HEAVY LIFTING

                }
        }
        return result //string
}

一种方法，我将调用这些方法A和B，做一些操作

a method in which i shall call those methods A and B, to do some operations

func displayResult
{
   1)  let a = asyncMethodA()
   2)  let b = asyncMethodB()
   3)  println(a + b) //some chaotic stuff might happen :(
}

所以问题是如何让（2）等待（1）运行，（3）等待（2）等等（那个） 1,2和3运行同步）？

so the question is how i could make that (2) waits for (1) to run, and (3) waits for (2) and so on (that 1,2 and 3 run syncronised)?

（我知道答案是将asyncMethodA和displayResult链接到asyncMethodB，但想知道如果有其他方法）

(i know that one answer is to chain asyncMethodA and displayResult into asyncMethodB, but want to know if there is some other method)

谢谢！。

推荐答案

func anAsyncMethod(resultHandler: (result: AnyObject) -> Void) {
    ...        
}

func anotherAsyncMethod(resultHandler: (result: AnyObject) -> Void) {
    ... 
}

let operationQueue = NSOperationQueue()

func performWithCompletionHandler(completion: (AnyObject?, AnyObject?) -> Void) {
        var resultOfOperation1: AnyObject?
        var resultOfOperation2: AnyObject?

        let operation1 = NSBlockOperation {
                let dispatchGroup = dispatch_group_create()
                dispatch_group_enter(dispatchGroup)
                self.anAsyncMethod {
                        result in
                        resultOfOperation1 = result
                        dispatch_group_leave(dispatchGroup)
                }
                // wait until anAsyncMethod is completed
                dispatch_group_wait(dispatchGroup, DISPATCH_TIME_FOREVER)
        }

        let operation2 = NSBlockOperation {
                let dispatchGroup = dispatch_group_create()
                dispatch_group_enter(dispatchGroup)
                self.anotherAsyncMethod {
                        result in
                        resultOfOperation2 = result
                        dispatch_group_leave(dispatchGroup)
                }
                // wait until anotherAsyncMethod is completed
                dispatch_group_wait(dispatchGroup, DISPATCH_TIME_FOREVER)
        }

        let completionOperation = NSBlockOperation {
                // send all results to completion callback
                completion(resultOfOperation1, resultOfOperation2)
        }

        // configuring interoperation dependencies
        operation2.addDependency(operation1)
        completionOperation.addDependency(operation2)

        operationQueue.addOperations([operation1, operation2, completionOperation], waitUntilFinished: false)
}

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