在Swift 2的闭包内部未分配类属性

Question

I am having trouble assigning a value to a property inside my Swift class. The property prints out fine inside the class but returns nil when accessed externally when calling the class method that assigns the property in the main viewController. Here is my class definition.

import Foundation

class NetworkConnection {

    var jsonObj: AnyObject?

    func makeHTTPRequest(data: String, location: String, completion: (jsonData: AnyObject?, error: NSError?) -> Void){

        var jsonData: AnyObject!

        let post: NSString = "data=\(data)"
        let url = NSURL(string: location)!
        let postData = post.dataUsingEncoding(NSUTF8StringEncoding)!

        let postLength = String(postData.length)
        let request = NSMutableURLRequest(URL: url)
        request.HTTPMethod = "POST"
        request.HTTPBody = postData
        request.setValue(postLength, forHTTPHeaderField: "Content-Length")
        request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
        request.setValue("application/json", forHTTPHeaderField: "Accept")

        let session = NSURLSession.sharedSession()

        let task = session.dataTaskWithRequest(request) { urlData, response, responseError in

            if let receiveData = urlData {

                let res = response as! NSHTTPURLResponse!

                if 200..<300 ~= res.statusCode {
                    do {
                        jsonData = try NSJSONSerialization.JSONObjectWithData(receiveData, options: NSJSONReadingOptions.init(rawValue:0))

                        completion(jsonData: jsonData, error: nil)
                    } catch let error as NSError {
                        let returnedError = NSError(domain: "validateUser", code: 3, userInfo: [
                            "title": "Made up title",
                            "message": "This is a messsage",
                            "cause": error
                            ])
                        completion(jsonData: nil, error: returnedError)
                    }
                }else{
                    let returnedError = NSError(domain: "validateUser", code: 1, userInfo: [
                        "title": "Second made up title",
                        "message": "This is another message"
                        ])
                    completion(jsonData: nil, error: returnedError)
                }
            }else{

                var userInfo: [NSObject: AnyObject] = [
                    "title": "Third made up title",
                    "message": "This is yet another message"
                ]
                if let error = responseError {
                    userInfo["message"] = error.localizedDescription
                    userInfo["cause"] = error
                }
                let returnedError = NSError(domain: "validateUser", code: 2, userInfo: userInfo)
                completion(jsonData: nil, error: returnedError)
            }


        }
        task.resume()

    }

    func validateUser(location: String, username: String, password: String) {

        let data = "&username=\(username)&password=\(password)"

        self.makeHTTPRequest(data, location: location) { jsonData, error in

            if let json = jsonData {

                self.jsonObj = json


                print(self.jsonObj)   // This shows property was assigned without errors

            }else{
                let userInfo = error!.userInfo
                let title = userInfo["title"] as! String
                let message = userInfo["message"] as! String
                print(title)
                print(message)
            }
        }
    }
}

This is the function that I call the validatUser() method in my viewController

@IBAction func login(sender: AnyObject) {

        let service = NetworkConnection()
        service.validateUser("http://myPhpServiceLink.com/mobile.login.php", username: usernameField.text!, password: passwordField.text!)

        if let serviceObj = service.jsonObj {

            print("success loading object \(serviceObj)")

        } else {

            print("error loading object from call \(service.jsonObj)")

        }
}

Here is the JSON data to be returned by PHP.

{"id":"1","username":"admin","message":"User is valid","error":null}

The line: print("service object = \\(self.jsonObj)") prints out the following in the console:

service object = Optional({
     error = "<null>";
     id = 1;
     message = "User is valid";
     username = admin;
})

But I get the "error loading object from call nil" from the @IBAction function. I've looked everywhere to find out why the property always returns nil when called externally and it is also hard to articulate my problem.

Answer 1

I bet this is due to your http request being performed in the background.
if let serviceObj = service.jsonObj is being executed before your validateUser method is completed. you need to rewrite `valdiateUser to take a completion handler.