完成处理程序不返回任何内容，即使它看起来像在单步执行时

Posted 2023-02-23

【中文标题】完成处理程序不返回任何内容，即使它看起来像在单步执行时

【英文标题】：completion handler not returning anything even though its looks like it is when stepping through it

【发布时间】：2018-03-13 18:17:42

【问题描述】：

这里是函数，它使用了 Operation(NSOperation)：

    typealias ResultType = Result<Data>
    typealias CompletionType = (ResultType) -> ()
    public var onCompletion: CompletionType?

  internal func getNetworkConnection(urlRequest: URLRequest, completionHandler: @escaping CompletionType)  

        let task = self.urlSession.dataTask(with: urlRequest, completionHandler:  [weak self] (data, response, error) in
            guard let strongSelf = self else 
                return
            

            if let errorResponse = error 
                //strongSelf.result = Result.failure(errorResponse)

                     strongSelf.onCompletion?(Result.failure(errorResponse))

            

             if let responseFromServer = response as? HTTPURLResponse,
                200...299 ~= responseFromServer.statusCode

                if let dataResponse = data
                    //strongSelf.result = Result.success(dataResponse)


                    strongSelf.onCompletion?(Result.success(dataResponse))//it hits this point 


                 else 
                    strongSelf.onCompletion?(Result.failure(NSError()))
                
             

            strongSelf.urlSession.invalidateAndCancel()
        )

        task.resume()
    

我正在为它编写一个单元测试，但它似乎没有在完成块中，即使它命中了：strongSelf.onCompletion?(Result.success(dataResponse))

到目前为止，单元测试是这样的：

func test_getNetworkConnection()

    let promise = expectation(description: "Completion handler invoked")

  sut?.getNetworkConnection(urlRequest: URLRequest(url: requestURL), completionHandler:  (data) in

        print(data) //never prints

        promise.fulfill()
    )

    wait(for: [promise], timeout: 100, enforceOrder: true)//exaggerated timeout but it fails
  //  XCTAssertTrue(returnedResponse!)

知道可能是什么问题吗？

【问题讨论】：

您是在测试实际连接还是在测试 Mock？

【参考方案1】：

你有一些问题。

在数据任务的完成块中，您正在调用strongSelf.onCompletion?...，但onCompletion 是nil，所以它什么也不做。 您的getNetworkConnection 函数有一个您从不使用的completionHandler 参数。 您对getNetworkConnection 的调用取决于被调用的completionHandler。

onCompletion 属性似乎没有意义。

在数据任务中，将对strongSelf.onCompletion?... 的调用替换为对completionHandler 参数的调用。

typealias ResultType = Result<Data>
typealias CompletionType = (ResultType) -> ()

internal func getNetworkConnection(urlRequest: URLRequest, completionHandler: @escaping CompletionType)  
    let task = self.urlSession.dataTask(with: urlRequest, completionHandler:  [weak self] (data, response, error) in
        guard let strongSelf = self else 
            return
        

        if let errorResponse = error 
            completionHandler(Result.failure(errorResponse))
        

        if let responseFromServer = response as? HTTPURLResponse,
            200...299 ~= responseFromServer.statusCode

            if let dataResponse = data
                completionHandler(Result.success(dataResponse))
             else 
                completionHandler(Result.failure(NSError()))
            
         else 
            // TODO - need to call completionHandler here too
        

        strongSelf.urlSession.invalidateAndCancel()
    )

    task.resume()

【讨论】：

做得很好。非常感谢！