活动指示器在执行时未显示

我试图在用户点击登录按钮时显示活动指示器。 如果我将startActivityIndicator()代码放在viewDidLoad()它将完全按预期显示在屏幕上。 当我执行它作为btnSignIn()第一步时，它永远不会出现。 有点失落，所以我希望Stack大师可以帮助……

 // 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() } 

Answer 1

使用我的delay实用程序（参见https://stackoverflow.com/a/24318861/341994 ），重写如下：

 @IBAction func btnSignIn(sender: AnyObject) { startActivityIndicator() delay(0.1) { if validateEmailAddress(txtEmailAddress.text!) == false { // ... everything else goes here ... } } 

延迟使活动指示器有机会出现并开始旋转。