Swift 3，未调用 URLSession 数据任务完成处理程序

Question

我正在编写一个库，所以不使用 UIKit，即使在我的 iOS 应用程序中，相同的代码也可以工作，但是当我在命令行中执行时不会。在 PlayGround 中，它似乎也可以工作。

由于某种原因回调没有被触发，所以打印语句没有执行。

internal class func post(request: URLRequest, responseCallback: @escaping (Bool, AnyObject?) -> ()) {
    execTask(request: request, taskCallback: { (status, resp)  -> Void in
            responseCallback(status, resp)
    })
}

internal class func clientURLRequest(url: URL, path: String, method: RequestMethod.RawValue,  params: Dictionary<String, Any>? = nil) -> URLRequest {
    var request = URLRequest(url: url)
    request.httpMethod = method
    do {
        let jsonData = try JSONSerialization.data(withJSONObject: (params! as [String : Any]), options: .prettyPrinted)

        request.setValue("application/json; charset=utf-8", forHTTPHeaderField: "Content-Type")
        request.httpBody = jsonData
    } catch let error as NSError {
        print(error)
    }
    return request
}

private class func execTask(request: URLRequest, taskCallback: @escaping (Bool,
    AnyObject?) -> ()) {

    let session = URLSession(configuration: URLSessionConfiguration.default)
    print("THIS LINE IS PRINTED")
    let task = session.dataTask(with: request, completionHandler: {(data, response, error) -> Void in
        if let data = data {
            print("THIS ONE IS NOT PRINTED")
            let json = try? JSONSerialization.jsonObject(with: data, options: [])
            if let response = response as? HTTPURLResponse , 200...299 ~= response.statusCode {
                taskCallback(true, json as AnyObject?)
            } else {
                taskCallback(false, json as AnyObject?)
            }
        }
    })
    task.resume()
}

Edits -：我正在编写一个库，所以不使用 UIKit，即使在我的 iOS 应用程序中，相同的代码也可以工作，但是当我在命令行中执行时不会。在 PlayGround 中，它似乎也可以工作。

Answer 1

我从头开始制作了一个简单的应用程序。 （Xcode 8 beta 6 / swift 3） 在控制器中，我粘贴了您的代码。 （加上网址创建..） 我在调试器中看到了所有内容：

这个是打印出来的

这个也是印刷的

我回来了

所以它似乎工作。

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let URLString = "https://apple.com"
        let url = URL(string: URLString)
        let request = URLRequest(url: url!)


        ViewController.execTask(request: request) { (ok, obj) in

            print("I AM BACK")

        }

    }

    private class func execTask(request: URLRequest, taskCallback: @escaping (Bool,
        AnyObject?) -> ()) {

        let session = URLSession(configuration: URLSessionConfiguration.default)
        print("THIS LINE IS PRINTED")
        let task = session.dataTask(with: request, completionHandler: {(data, response, error) -> Void in
            if let data = data {
                print("THIS ONE IS PRINTED, TOO")
                let json = try? JSONSerialization.jsonObject(with: data, options: [])
                if let response = response as? HTTPURLResponse , 200...299 ~= response.statusCode {
                    taskCallback(true, json as AnyObject?)
                } else {
                    taskCallback(false, json as AnyObject?)
                }
            }
        })
        task.resume()
    }

}

Answer 2

我知道答案迟了，但如果你还没有弄清楚问题或在其他地方遇到问题，让我们试试这个。

您需要将会话变量保存在方法范围之外（使其成为实例变量）。由于您在函数范围内本地定义了它。它在完成处理程序可以被调用之前被释放，记住完成处理程序不能保留你的会话对象，并且在运行循环执行之后，垃圾收集器将释放你的会话对象。每当我们想从委托或完成处理程序中回调时，我们都需要保留这些对象..

self.session = URLSession(configuration: URLSessionConfiguration.default)

Answer 3

这里建议的更改是否进行了，现在可以使用了。

Using NSURLSession from a Swift command line program

var sema = DispatchSemaphore( value: 0 )

private func execTask(request: URLRequest, taskCallback: @escaping (Bool,
    AnyObject?) -> ()) {

    let session = URLSession(configuration: URLSessionConfiguration.default, delegate: self, delegateQueue: nil )

    session.dataTask(with: request) {(data, response, error) -> Void in
        if let data = data {
            let json = try? JSONSerialization.jsonObject(with: data, options: [])
            if let response = response as? HTTPURLResponse , 200...299 ~= response.statusCode {
                taskCallback(true, json as AnyObject?)
            } else {
                taskCallback(false, json as AnyObject?)
            }
        }
    }.resume()
    sema.wait()
}

Answer 4

let dataTask = session.dataTask(with: request, completionHandler: {data, response,error -> Void in 
    print("Request : \(response)")

    let res = response as! HTTPURLResponse

    print("Status Code : \(res.statusCode)")

    let strResponse = NSString(data: data!, encoding: String.Encoding.utf8.rawValue)
    print("Response String :\(strResponse)")
    })
dataTask.resume()

Answer 5

斯威夫特 3.0

只需将以下代码复制到您的视图控制器中即可。

@IBAction func btnNewApplicationPressed (_ sender: UIButton) {
        callWebService()
}

func callWebService() {
    // Show MBProgressHUD Here
    var config                              :URLSessionConfiguration!
    var urlSession                          :URLSession!
    
    config = URLSessionConfiguration.default
    urlSession = URLSession(configuration: config)
    
    // MARK:- HeaderField
    let HTTPHeaderField_ContentType         = "Content-Type"
    
    // MARK:- ContentType
    let ContentType_ApplicationJson         = "application/json"
    
    //MARK: HTTPMethod
    let HTTPMethod_Get                      = "GET"
    
    let callURL = URL.init(string: "https://itunes.apple.com/in/rss/newapplications/limit=10/json")
    
    var request = URLRequest.init(url: callURL!)
    
    request.timeoutInterval = 60.0 // TimeoutInterval in Second
    request.cachePolicy = URLRequest.CachePolicy.reloadIgnoringLocalCacheData
    request.addValue(ContentType_ApplicationJson, forHTTPHeaderField: HTTPHeaderField_ContentType)
    request.httpMethod = HTTPMethod_Get
    
    let dataTask = urlSession.dataTask(with: request) { (data,response,error) in
        if error != nil{
            return
        }
        do {
            let resultJson = try JSONSerialization.jsonObject(with: data!, options: []) as? [String:AnyObject]
            print("Result",resultJson!)
        } catch {
            print("Error -> \(error)")
        }
    }
    
    dataTask.resume()
}

Answer 6

有时，对我来说，在这些情况下未调用 completionHandler 的解决方案是因为 Info.plist 上的“允许任意加载”标志被定义为 NO。

Allow Arbitrary loads flag defined as YES