Ich versuche, eine Aktivitätsanzeige anzuzeigen, wenn der Benutzer auf die Anmeldeschaltfläche klickt. Wenn ich dasstartActivityIndicator() code inviewDidLoad() Es wird genau wie erwartet auf dem Bildschirm angezeigt. Wenn ich es als ersten Schritt in @ ausführbtnSignIn() es erscheint nie. Ein bisschen verloren, also hoffe ich, dass die Stack-Gurus helfen können ...

// Here are the variable declarations
var activityIndicator: UIActivityIndicatorView = UIActivityIndicatorView()
var loadingView: UIView = UIView()
var viewCenter:CGPoint!

@IBAction func btnSignIn(sender: AnyObject) {

    startActivityIndicator()

    if validateEmailAddress(txtEmailAddress.text!) == false {
        stopActivityIndicator(self.loadingView)
        return
    }

    if validatePassword(txtPassword.text!) == false {
        stopActivityIndicator(self.loadingView)
        return
    }

    PFUser.logInWithUsernameInBackground(txtEmailAddress.text!, password:txtPassword.text!) {
        (user: PFUser?, error: NSError?) -> Void in
        if user != nil {

            // Successful login.
            self.txtPassword.resignFirstResponder()
            self.txtEmailAddress.resignFirstResponder()

            self.getUserInfo()

        } else {
            self.stopActivityIndicator(self.loadingView)
            // The login failed. Display alert.
            self.displayAlert("Whoops!", message: "Email or Password are incorrect.")
        }
    }
}

func startActivityIndicator() {

    loadingView.frame = CGRectMake(0, 0, 80, 80)
    loadingView.center = viewCenter
    print(viewCenter)
    loadingView.backgroundColor = UIColorFromRGB("444444", alpha: 0.7)
    loadingView.clipsToBounds = true
    loadingView.layer.cornerRadius = 10

    activityIndicator.frame = CGRectMake(0.0, 0.0, 40.0, 40.0);
    activityIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.WhiteLarge
    activityIndicator.center = CGPointMake(loadingView.frame.size.width / 2, loadingView.frame.size.height / 2);

    view.addSubview(loadingView)
    loadingView.addSubview(activityIndicator)

    UIApplication.sharedApplication().beginIgnoringInteractionEvents()

    activityIndicator.startAnimating()

}

func stopActivityIndicator(uiView: UIView) {

    activityIndicator.stopAnimating()
    loadingView.removeFromSuperview()
    UIApplication.sharedApplication().endIgnoringInteractionEvents()
}