ios - 预期返回 'NSURLSessionDataTask' 的函数中缺少返回值

Question

我正在学习有关访问 API 和解析结果的教程。我正在逐字逐句地学习教程，但由于“预期返回‘NSURLSessionDataTask’的函数中缺少返回值”，我无法运行该程序

所以我将返回语句更改为“return NSURLSessionDataTask”，但随后收到错误消息“无法将类型为‘NSURLSessionDataTask.Type’的返回表达式转换为返回类型‘NSURLSessionDataTask’

我如何确定返回类型？我什至需要返回吗？因为在教程中没有 return 语句(我也试过没有 return )。

func dataTaskWithRequest(request: NSURLRequest, completionHandler: (NSData?, NSURLResponse?, NSError?) -> Void)
    -> NSURLSessionDataTask {

    let postEndpoint: String = "http://jsonplaceholder.typicode.com/posts/1"
    let urlRequest = NSURLRequest(URL: NSURL(string: postEndpoint)!)


    let config = NSURLSessionConfiguration.defaultSessionConfiguration()
    let session = NSURLSession(configuration: config)


        let task = session.dataTaskWithRequest(urlRequest, completionHandler: {
            (data, response, error) in            

        guard let responseData = data else {
            print("Error: did not recieve data")
            return
        }
        guard error == nil else {
            print("error calling GET on /posts/1")
            print(error)
            return
        }
        // parse the resutl as JSON, since that's what the API provieds
        let post: NSDictionary
        do {
            post  = try NSJSONSerialization.JSONObjectWithData(responseData, options: []) as! NSDictionary
        } catch {
            print("error trying to convert data to JSON")
            return
        }
        // now we have the post, let's just print it to prove we can access it

        print("The post is: " + post.description)

            if let postTitle = post["title"] as? String {
                print("The title is: " + postTitle)
            }




    })

    // and send it
    task.resume()



}

Answer 1

您真的打算编写自己的名为 dataTaskWithRequest 的方法，它看起来就像同名的 NSURLSession 方法吗？问题是你说你正在编写一个返回 NSURLSessionTask 对象的方法，但你没有返回任何东西。

我认为您的意思类似于以下内容，将您自己的方法重命名为其他内容，并指定它本身不返回任何内容，因为它不是:

func performRequest() {
    let postEndpoint: String = "http://jsonplaceholder.typicode.com/posts/1"
    let urlRequest = NSURLRequest(URL: NSURL(string: postEndpoint)!)

    let config = NSURLSessionConfiguration.defaultSessionConfiguration()
    let session = NSURLSession(configuration: config)

    let task = session.dataTaskWithRequest(urlRequest, completionHandler: {
        (data, response, error) in

        guard let responseData = data else {
            print("Error: did not recieve data")
            return
        }
        guard error == nil else {
            print("error calling GET on /posts/1")
            print(error)
            return
        }
        // parse the resutl as JSON, since that's what the API provieds
        let post: NSDictionary
        do {
            post  = try NSJSONSerialization.JSONObjectWithData(responseData, options: []) as! NSDictionary
        } catch {
            print("error trying to convert data to JSON")
            return
        }
        // now we have the post, let's just print it to prove we can access it

        print("The post is: " + post.description)

        if let postTitle = post["title"] as? String {
            print("The title is: " + postTitle)
        }
    })

    // and send it
    task.resume()
}