ios - swift 4 : Navigation Controller unwanted looping

Question

我有以下代码:

import UIKit
import FacebookLogin

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        if AccessToken.current != nil {
            // Already logged-in
            // Redirect to Home View Controller
            goToHome()
        }

        // Add LoginButton
        let loginButton = FBLoginButton(permissions: [ .publicProfile, .email, .userFriends ])
        let screenSize:CGRect = UIScreen.main.bounds
        let screenHeight = screenSize.height // real screen height
        //let's suppose we want to have 10 points bottom margin
        let newCenterY = screenHeight - loginButton.frame.height - 20
        let newCenter = CGPoint(x: view.center.x, y: newCenterY)
        loginButton.center = newCenter
        view.addSubview(loginButton)

        // Triggered after every successfully login / logout
        NotificationCenter.default.addObserver(forName: .AccessTokenDidChange, object: nil, queue: OperationQueue.main) { [weak self] _ in
            if AccessToken.current != nil {
                // Successfully just Logged in
                // Redirect to Home View Controller
                self?.goToHome()
            } else {
                // Successfully just Logged out
            }
        }
    }

    func goToHome() {
        let storyboard = UIStoryboard(name: "HomeAfterLogIn", bundle: nil)
        let vc = storyboard.instantiateViewController(withIdentifier: "HomeAfterLogInViewController") // I called mine like that (check screenshot below)
        self.navigationController?.pushViewController(vc, animated: true)
    }

}

此代码允许用户使用 Facebook SDK 登录我的应用程序。 LaunchScreen.storyboard 如下:



然后导致 Main.storyboard，它看起来像这样:



如果用户登录成功，会被带到HomeAfterLogIn.storyboard，如下图:



但是，一旦用户登录，即用户成功登录，此页面就会持续加载，显示“已登录”标签，然后一遍又一遍地重新加载，而我只想加载一次。如果用户之前登录过，页面只加载一次，代码如下:

if AccessToken.current != nil {
            // Already logged-in
            // Redirect to Home View Controller
            goToHome()
        }

但是如果用户是新用户/第一次使用，它会循环，所以我认为错误在这里:

// Triggered after every successfully login / logout
        NotificationCenter.default.addObserver(forName: .AccessTokenDidChange, object: nil, queue: OperationQueue.main) { [weak self] _ in
            if AccessToken.current != nil {
                // Successfully just Logged in
                // Redirect to Home View Controller
                self?.goToHome()
            } else {
                // Successfully just Logged out
            }
        }

Answer 1

我可以从你的最后一张截图中看到你的 HomeAfterLogInViewController 在 storyboard 中您已设置 自定义类 归因于 ViewController这意味着您正在将 HomeAfterLogInViewController 的 UI 与 ViewController.swift 链接起来。看来你陷入了困境。

每个 Storyboard UI ViewController 都必须链接到一个代表特定 ViewController 逻辑的 swift 类。

这意味着在您的上一个屏幕截图中，您会在右侧的自定义类中看到将 ViewController 替换为 HomeAfterLogInViewController (应该与您拥有的文件名相同 HomeAfterLogInViewController.swift )