ios - 共享变量

Question

在构建我的第一个应用程序时跌跌撞撞。尝试将变量从一个 View Controller (“ViewController”)传递到另一个 View Controller (“SecondViewController”)。我在 Stack Overflow 上找到了一些代码，但收到错误，并且不确定我做错了什么。在第一个 View Controller 中，我有:

func prepareForSegue(segue: UIStoryboardSegue!, sender: Any!) {
                        if (segue.identifier == "segueTest") {
                        //Checking identifier is crucial as there     might be multiple
                        // segues attached to same view
                        var secondVC = segue!.SecondViewController as     ViewController;
                        secondVC.toPass =  "email"

                            }
                        }

在第二个 View Controller 中我有:

var toPass:字符串!

我在第一个 View Controller 中收到错误:“类型的值没有成员”(参见图片)

我很困惑这是为什么。如果有任何建议，我将不胜感激。 2

(Swift 3？)我发布了下面两个 View Controller 的所有代码，看看是否有帮助。对于代码的困惑，我深表歉意。这是第一个 View Controller 代码:

import UIKit
import FBSDKLoginKit

extension UserDefaults {
    // check for is first launch - only true on first invocation    after app install and sends user to answer questions

    static func isFirstLaunch() -> Bool {
        let hasBeenLaunchedBeforeFlag = "hasBeenLaunchedBeforeFlag"
        let isFirstLaunch = !UserDefaults.standard.bool(forKey: hasBeenLaunchedBeforeFlag)
        if (isFirstLaunch) {
            UserDefaults.standard.set(true, forKey: hasBeenLaunchedBeforeFlag)
            UserDefaults.standard.synchronize()
        }

        print(hasBeenLaunchedBeforeFlag)
        return isFirstLaunch
    }
}

class ViewController: UIViewController, FBSDKLoginButtonDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()

        let loginButton = FBSDKLoginButton()
        view.addSubview(loginButton)
        loginButton.frame = CGRect(x: 16, y: 350, width:   view.frame.width - 32, height: 50)
        loginButton.delegate = self

        self.view.backgroundColor = UIColor(patternImage:   UIImage(named:"Book Funnel")!)

    }

    func loginButtonDidLogOut(_ loginButton: FBSDKLoginButton!) {
        print("Did log out of Facebook")
    }

    //Gather Facebook demographic information

    func loginButton(_ loginButton: FBSDKLoginButton!, didCompleteWith result: FBSDKLoginManagerLoginResult!, error: Error!) {
        if error != nil {
            print(error)
            return
        }

        let login: FBSDKLoginManager = FBSDKLoginManager()
        // Make login and request permissions
        login.logIn(withReadPermissions: ["email", "public_profile"], from: self, handler: {(result, error) -> Void in

            if error != nil {
                // Handle Error
                NSLog("Process error")
            } else if (result?.isCancelled)! {
                // If process is cancel
                NSLog("Cancelled")
            }
            else {
                // Parameters for Graph Request
                let parameters = ["fields": "email, name"]

                FBSDKGraphRequest(graphPath: "me", parameters: parameters).start {(connetion, result, error) -> Void in
                    if error != nil {
                        NSLog(error.debugDescription)
                        return
                    }

                    // Result
                    print("Result: \(result)")

                    // Handle vars
                    if let result = result as? [String:String],
                        let email: String = result["email"],
                        let fbId: String = result["id"] {
                        print("Email: \(email)")
                        print("fbID: \(fbId)")

                        func prepareForSegue(segue: UIStoryboardSegue?, sender: AnyObject?) {
                            if segue!.identifier == "segueTest" {
                                if let secondVC = segue!.SecondViewController as? ViewController {
                                    secondVC.toPass =  "email"
                                }
                            }
                        }


                }
                }
            }
        })


    func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.

            }
        }
    }

第二个 View Controller 代码:

import UIKit
import FBSDKCoreKit
import FBSDKLoginKit


class SecondViewController: UIViewController {


    @IBOutlet weak var sliderLabel: UILabel!

    @IBOutlet weak var verticalSlider: UISlider!
           {
                didSet{
                    verticalSlider.transform =   CGAffineTransform(rotationAngle: CGFloat(-M_PI_2))


                }
        }

        //Change label as slider moves

        @IBAction func verticalSliderChanged(_ sender: UISlider) {

            var currentValue = Double(sender.value);

            sliderLabel.text = "\(currentValue)"

    }

    @IBOutlet weak var ratingSubmitted: UIButton!

    @IBAction func checkmarkPressed(_ sender: Any) {


                func viewDidLoad() {
                super.viewDidLoad()

                self.view.backgroundColor = UIColor(patternImage:   UIImage(named:"Book Funnel")!)

            }
    }


    @IBOutlet weak var checkmarkButton: UIButton!

    @IBAction func checkmarkButtonPressed(_ sender: Any) {

        let img:UIImageView = UIImageView(frame: CGRect(x: 30, y: 180, width: 250, height: 320))

    let randomImage = arc4random()
    if (randomImage % 3 == 0) {
    img.image = UIImage(named: "hero.jpg")
    } else if (randomImage % 3 == 1) {
    img.image = UIImage(named: "hillary.jpg")
    } else {
    img.image = UIImage(named: "thistimeisdifferent.jpg")
    }


    //        img.contentMode = UIViewContentMode.ScaleAspectFill
    //        img.backgroundColor = UIColor.redColor()
    self.view.addSubview(img)

        var toPass: String!

    }


            override func didReceiveMemoryWarning() {
                super.didReceiveMemoryWarning()
                // Dispose of any resources that can be recreated.

            }


            }

Answer 1

您对第二个 View Controller 的转换是错误的，因此它不知道其中的变量toPass。

尝试更改此设置:

var secondVC = segue!.SecondViewController as     ViewController;

对此:

if let secondVC = segue.destination as? SecondViewController {
    secondVC.toPass =  "email"
}