课程笔记文集地址：Udemy课程：The Complete iOS 9 Developer Course - Build 18 Apps
Section 8 主要的内容是克隆 Instagram：107 - 128课。
本节课主要是解决如何创建一个旋转（正在加载中）和提示框。
1、Spinner
var activityIndicator: UIActivityIndicatorView = UIActivityIndicatorView()
activityIndicator = UIActivityIndicatorView(frame: CGRectMake(0, 0, 50, 50))
activityIndicator.center = self.view.center
activityIndicator.hidesWhenStopped = true
activityIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.Gray
view.addSubview(activityIndicator)
//开始旋转
activityIndicator.startAnimating()
//结束旋转
activityIndicator.stopAnimating()
2、提示框
let alert = UIAlertController(title: "Hey there!", message: "Are you sure?", preferredStyle: UIAlertControllerStyle.Alert)
let action = UIAlertAction(title: "OK", style: .Default, handler: { (action) -> Void in
self.dismissViewControllerAnimated(true, completion: nil)
})
alert.addAction(action)
self.presentViewController(alert, animated: true, completion: nil)
