如何在iPhone版swift iOS中使用FBSDK获取用户邮箱？

import FBSDKCoreKit
import FBSDKLoginKit

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    ApplicationDelegate.shared.application(application, didFinishLaunchingWithOptions: launchOptions)
    return true
}

let loginManager = LoginManager()
loginManager.logIn(permissions: ["email"], from: self) { (result, error) in
    if let error = error {
        print("登录失败：\(error.localizedDescription)")
    } else if result?.isCancelled == true {
        print("用户取消登录")
    } else {
        if AccessToken.current != nil {
            let graphRequest = GraphRequest(graphPath: "me", parameters: ["fields": "email"])
            graphRequest.start { (connection, result, error) in
                if let error = error {
                    print("获取用户邮箱失败：\(error.localizedDescription)")
                } else if let result = result as? [String: Any], let email = result["email"] as? String {
                    print("用户邮箱：\(email)")
                }
            }
        }
    }
}