ios - 未调用 PFLogInViewControllerDelegate 函数

Question

在使用PFLogInViewController（或它的子类）时，看起来里面的任何函数PFLogInViewControllerDelegate都没有被调用过。尽管主 ViewController 声明符合协议并且设置了对象PFLogInViewControllerDelegate的委托。PFLogInViewController

还有其他事情要做吗？

这是相关代码，尽管我认为它不会带来比上面写的更多的东西：

class ViewController: UIViewController, PFLogInViewControllerDelegate {
    var loginVC:PFLogInViewController!
    ....
    func someFunc() {
        if (loginVC == nil) {
            loginVC = PFLogInViewController()
            loginVC.delegate = self
        }

        self.navigationController?.pushViewController(loginVC, animated: true)
    }
    ....
    // MARK: - PFLogInViewControllerDelegate

    // Sent to the delegate to determine whether the log in request should be submitted to the server.
    func logInViewController(logInController: PFLogInViewController,
                             shouldBeginLogInWithUsername username:String,
                             password: String) -> Bool {
        print(#function) // THIS IS NEVER CALLED!!!

        return true
    }


    // Sent to the delegate when a PFUser is logged in.
    func logInViewController(logInController: PFLogInViewController, didLogInUser user: PFUser) {
        print(#function) // THIS IS NEVER CALLED!!!
    }
}