一次登錄后，Facebook SDK ios登錄按鈕消失

Question

我正在嘗試實現Facebook登錄。 我通過一些教程使它工作，但是登錄一次並重新打開該應用程序之后。 登錄按鈕消失了。 我嘗試清理項目，然后重新打開，然后在重新創建整個項目時發生了同樣的折磨。 這是我的代碼：

應用程序委托：

//
//  AppDelegate.swift
//  Click
//
//  Created by Emlyn Mileaf-Patel on 11/29/15.
//  Copyright © 2015 Emlyn Mileaf-Patel. All rights reserved.
//
// borrowed code from: http://www.brianjcoleman.com/tutorial-how-to-use-login-in-facebook-sdk-4-0-for-swift/

import UIKit
import FBSDKCoreKit
import FBSDKLoginKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        // Override point for customization after application launch.
        return FBSDKApplicationDelegate.sharedInstance().application(application, didFinishLaunchingWithOptions: launchOptions)
    }

    func application(application: UIApplication,
        openURL url: NSURL,
        sourceApplication: String?,
        annotation: AnyObject) -> Bool {
            return FBSDKApplicationDelegate.sharedInstance().application(
                application,
                openURL: url,
                sourceApplication: sourceApplication,
                annotation: annotation)
    }

    func applicationWillResignActive(application: UIApplication) {
        // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
        // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
    }

    func applicationDidEnterBackground(application: UIApplication) {
        // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
        // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
    }

    func applicationWillEnterForeground(application: UIApplication) {
        // Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
    }

    func applicationDidBecomeActive(application: UIApplication) {
        // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
    }

    func applicationWillTerminate(application: UIApplication) {
        // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    }


}

視圖控制器：

//
//  ViewController.swift
//  FacebookTutorial
//
//  Created by Brian Coleman on 2015-03-27.
//  Copyright (c) 2015 Brian Coleman. All rights reserved.
//

import UIKit
import FBSDKCoreKit
import FBSDKLoginKit

class ViewController: UIViewController, FBSDKLoginButtonDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        if (FBSDKAccessToken.currentAccessToken() != nil)
        {
            // User is already logged in, do work such as go to next view controller.
        }
        else
        {
            let loginView : FBSDKLoginButton = FBSDKLoginButton()
            self.view.addSubview(loginView)
            loginView.center = self.view.center
            loginView.readPermissions = ["public_profile", "email", "user_friends"]
            loginView.delegate = self
        }

    }

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

    // Facebook Delegate Methods

    func loginButton(loginButton: FBSDKLoginButton!, didCompleteWithResult result: FBSDKLoginManagerLoginResult!, error: NSError!) {
        print("User Logged In")

        if ((error) != nil)
        {
            // Process error
        }
        else if result.isCancelled {
            // Handle cancellations
        }
        else {
            // If you ask for multiple permissions at once, you
            // should check if specific permissions missing
            if result.grantedPermissions.contains("email")
            {
                // Do work
            }
        }
    }

    func loginButtonDidLogOut(loginButton: FBSDKLoginButton!) {
        print("User Logged Out")
    }

    func returnUserData()
    {
        let graphRequest : FBSDKGraphRequest = FBSDKGraphRequest(graphPath: "me", parameters: nil)
        graphRequest.startWithCompletionHandler({ (connection, result, error) -> Void in

            if ((error) != nil)
            {
                // Process error
                print("Error: \(error)")
            }
            else
            {
                print("fetched user: \(result)")
                let userName : NSString = result.valueForKey("name") as! NSString
                print("User Name is: \(userName)")
                let userEmail : NSString = result.valueForKey("email") as! NSString
                print("User Email is: \(userEmail)")
            }
        })
    }
}

Answer 1

我認為您的問題在這里：

if (FBSDKAccessToken.currentAccessToken() != nil)
        {
            // User is already logged in, do work such as go to next view controller.
        }
        else
        {
            let loginView : FBSDKLoginButton = FBSDKLoginButton()
            self.view.addSubview(loginView)
            loginView.center = self.view.center
            loginView.readPermissions = ["public_profile", "email", "user_friends"]
            loginView.delegate = self
        }

調試並檢查在加載視圖時輸入的語句，看來FBSDKAccessToken.currentAccessToken()不為nil。