Ios graphRequest.start不返回任何数据

我正在使用FacebookSDK使用Swift 3登录iOS

这是我的密码。问题是没有返回值

import UIKit

类ViewController:UIViewController{

@IBOutlet weak var email: UITextField!
@IBOutlet weak var password: UITextField!
@IBOutlet weak var uLoginButton: UIButton!

let loginButton: FBSDKLoginButton = {

    let button = FBSDKLoginButton()

    button.readPermissions = ["email"]

    return button;

}()

override func viewDidLoad() {
    super.viewDidLoad()

    view.addSubview(loginButton);
    loginButton.center = view.center
    loginButton.delegate = self

    if (FBSDKAccessToken.current() != nil) {
        fetchProfile();
    }

    self.style()
}

func fetchProfile(){

    let graphRequest = FBSDKGraphRequest(graphPath: "me", parameters: ["fields" : "email, name, first_name, last_name, picture.type(large)"])

    let connection = FBSDKGraphRequestConnection()

    connection.add(graphRequest, completionHandler: { (connection, result, error) in

        if error != nil {

            //do something with error
            print("No Data returned")
            print(result)
        } else {

            //do something with result
            print("Data returned")
            print(result)

        }

    })

    connection.start()

}

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

func style(){
    self.email.layer.cornerRadius = 15;
    self.password.layer.cornerRadius = 15;
    self.uLoginButton.layer.cornerRadius = 15;

}

}

扩展视图控制器：FBSDKLoginButtonDelegate{

internal func loginButton(_ loginButton: FBSDKLoginButton!, didCompleteWith result: FBSDKLoginManagerLoginResult!, error: Error!) {

    // when the login is correct!
    print("Success login!");
    fetchProfile()
}

internal func loginButtonDidLogOut(_ loginButton: FBSDKLoginButton!) {
    FBSDKAppEvents.activateApp()
}

internal func loginButtonWillLogin(_ loginButton: FBSDKLoginButton!) -> Bool {
    return true
}

---

}

在Swift 3中，这是执行图形请求的方式

初始化FBSDKGraphRequest

初始化FBSDKGraphRequestConnection

添加请求到请求连接

启动连接

所以

---

你好这次跑步很好！但是，我不想获取数据（电子邮件、用户名等）。。。我正在使用“打印（结果）”进行测试，但是没有返回任何数据。在这种情况下，您调用graph request时可能没有facebook用户。您是在用户登录之前还是之后调用此函数？方法是在单击按钮时调用此函数。由于没有字段类型“picture.type（large）”，因此该函数可能不会返回任何内容。尝试不使用它的图形请求。此处列出了可用字段的列表：

let graphRequest = FBSDKGraphRequest(graphPath: "me", parameters: ["fields" : "email"])
    let connection = FBSDKGraphRequestConnection()
    connection.add(graphRequest, completionHandler: { (connection, result, error) in

        if error != nil {

            //do something with error

        } else {

            //do something with result

        }

    })

    connection.start()