我想在用户输入登录凭据并单击登录按钮后显示活动指示器。这看起来很简单，但是当我运行（构建成功）时指示器没有显示。我不确定这是否是因为当应用程序真正运行时，它会将凭据传递给服务器进行验证，但该代码尚未激活，所以登录是即时的，或者我写错了但没有导致错误。感谢您的帮助。
@IBAction func loginButtonTapped(sender: AnyObject) {
//add error checking for loginEntered and passwordEntered if they are blank
if loginEntered.text == "" || passwordEntered.text == "" {
//Define the variable error for the message that should be displayed
self.alertError = "Please enter your Login ID and/or Password"
}
if self.alertError != "" { //if there is an error with the login
//Display the error message on screen
self.displayAlert("Missing Required Information", error: alertError)
//reset error variable
self.alertError = ""
//return the user to the LoginID field and empty it if there is data in it. Empty the password field too. ?? How do I do that??
} else { //the login ID and password are entered
//setup for a spinner to notify the user the app is working on something
activityIndicator = UIActivityIndicatorView(frame: CGRectMake(0, 0, 80, 80))
activityIndicator.center = self.view.center;
activityIndicator.backgroundColor = (UIColor(white: 0.3, alpha: 0.5)) //creates a background behind the spinner
activityIndicator.layer.cornerRadius = 10
activityIndicator.hidesWhenStopped = true
activityIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.WhiteLarge
view.addSubview(activityIndicator)
activityIndicator.startAnimating()
UIApplication.sharedApplication().beginIgnoringInteractionEvents()
该代码基于登录凭据和从服务器返回的数据继续执行多个 if 语句。最后，停止忽略交互事件。最后，我将相同的代码放入 IBAction 中，用于我为测试代码而创建的按钮。它适用于按钮。