如果您的用户通过Facebook登录，则如何编程启动到另一个ViewController

Question

基本上我有一个名为facebooklogin.swift，登录页面和viewController.swift主页的类。我已经正确地编码了所有Facebook登录功能，所有这些都可以使用，我可以使用FBSDK提供的按钮以及我定义的自定义按钮登录并注销。但是，如果用户已登录，我无法弄清楚如何转到ViewController.swift页面。

这是Facebooklogin.swift代码：

import UIKit
import FBSDKCoreKit
import FBSDKLoginKit
class facebookLogin: UIViewController, FBSDKLoginButtonDelegate {
    var loginStatus = false;
    @IBOutlet weak var facebookOutlet: UIButton!
    override func viewDidLoad() {
        super.viewDidLoad()
        super.viewDidLoad()
        let loginButton  = FBSDKLoginButton()
        view.addSubview(loginButton)
        loginButton.center = view.center
        loginButton.delegate = self;
        loginButton.readPermissions = ["email","public_profile"]
    }
    @IBAction func facebookAction(_ sender: Any) {
        customFBLogin()
        if (FBSDKAccessToken.current() != nil) {
            NSLog("it works")
        }
    }
    func customFBLogin() {
        FBSDKLoginManager().logIn(withReadPermissions: ["email","public_profile"], from: self) { (result, err) in
            if err != nil {
                print("Facebook Login Error Failed (err)")
                return;
            }
            self.showEmailAddress();
            self.loginStatus = true;
        }
    }

    func loginButtonDidLogOut(_ loginButton: FBSDKLoginButton!) {
        print("Did log out of Facebook")
    }
    func loginButton(_ loginButton: FBSDKLoginButton!, didCompleteWith result: FBSDKLoginManagerLoginResult!, error: Error!) {
        if error != nil {
            print(error)
            return;
        } else {
            print("Successfuly logged into Facebook");
            showEmailAddress()
        }
    }
    func showEmailAddress() {
        FBSDKGraphRequest(graphPath: "/me", parameters: ["fields": "id, name, email"]).start(completionHandler: { (connection, result, err) in
            if err != nil {
                print("Failed to start graph request (err)")
                return;
            }
            print(result)
        })
    }

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

    /*
    // MARK: - Navigation
    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        // Get the new view controller using segue.destinationViewController.
        // Pass the selected object to the new view controller.
    }
    */
}

这是appdelegate.swift文件的相关代码：

import UIKit
import CoreData
import Firebase
import FBSDKCoreKit
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        FIRApp.configure()
        FBSDKApplicationDelegate.sharedInstance().application(application, didFinishLaunchingWithOptions: launchOptions)
        let mainStoryBoard = UIStoryboard.init(name: "Main", bundle: nil)
        self.window = UIWindow(frame: UIScreen.main.bounds)
        var initialViewController: UIViewController
        if(FBSDKAccessToken.current() != nil) {
            let vc = mainStoryBoard.instantiateViewController(withIdentifier: "ViewController") as! ViewController
            initialViewController = vc
        } else{
            initialViewController = mainStoryBoard.instantiateViewController(withIdentifier: "facebookLogin")
        }
        self.window?.rootViewController = initialViewController
        self.window?.makeKeyAndVisible()
        return true
    }
    func application(_ app: UIApplication, open url: URL, options: [UIApplicationOpenURLOptionsKey : Any] = [:]) -> Bool {
        let handled = FBSDKApplicationDelegate.sharedInstance().application(app, open: url, sourceApplication: options[UIApplicationOpenURLOptionsKey.sourceApplication] as! String!, annotation: options[UIApplicationOpenURLOptionsKey.annotation])
        return handled;
    }

在AppDelegate.Swift类中的第一个应用程序功能中，我在Stackoverflow上找到了另一个使用此代码的教程。我输入了代码并将语法转换为swift3，但是当我启动时，该应用程序会断开。这意味着它知道我已登录，但是由于某种原因，SEGUE不会加载并打破了应用程序。我得到的错误是线程1：sigabrt。

这是故事板中的相关项目的外观，首先，初始视图控制器在左侧，如果用户已记录在我希望该应用程序中，请从右侧的ViewController开始1

Answer 1

您的代码似乎还可以。您应该考虑在故事板设计屏幕中的身份部分中查看ViewController的故事板ID。您应该将故事板ID作为" ViewController"。登录屏幕的故事板ID应根据您的代码为" FacebookLogin"。

Answer 2

swift 3代码

//检查Last Accestoken

    if let accessToken = AccessToken.current {
        print("Last AccesToken -(accessToken)")
        // Redirect to next screen
        self.performSegue(withIdentifier:"NextScreen", sender: self)
    }
    else {
        let loginManager = LoginManager()
        loginManager.loginBehavior = LoginBehavior.web
        loginManager.logIn([ .publicProfile , .email, .userFriends], viewController: self) { loginResult in
            switch loginResult {
            case .failed(let error):
                print(error)
                break
            case .cancelled:
                print("User cancelled login.")
                break
            case .success(let grantedPermissions, let declinedPermissions, let accessToken):
                print("Logged in! (grantedPermissions) (accessToken) (declinedPermissions)")
                // Save Current UserInfo
                let params = ["fields":"id,name,email,picture"]
                let graphRequest = GraphRequest(graphPath: "me", parameters: params)
                graphRequest.start { (urlResponse, requestResult) in
                    switch requestResult {
                    case .failed(let error):
                        print(error)
                    case .success(let graphResponse):
                        if let responseDictionary = graphResponse.dictionaryValue {
                            print("(String(describing: graphResponse.dictionaryValue))")
                            UserDefaults.standard.set(responseDictionary, forKey: "userInfo")
                        }
                    }
                }
                self.performSegue(withIdentifier: "NextScreen", sender: self)
                break
            }
        }
    }