创建单例类

class Manager: NSObject {
    static let manager = Manager()
    
    static func shared() -> Manager {
        //返回同一个对象
        return manager
    }
    
    static var name: String!
}

ViewDidLoad

 override func viewDidLoad() {
        super.viewDidLoad()        
        Manager.shared().name = "Zhangsan"

        print(Manager.name)
        
        //1. UIApplication
        //单例类: 只有一个对象
        let app = UIApplication.sharedApplication()
        let us = NSUserDefaults.standardUserDefaults()
        
        //程序局部性
        let fileManager = NSFileManager.defaultManager()
        
    }

找Window的三个方法:

        let window = UIApplication.sharedApplication().keyWindow
        let window = UIApplication.sharedApplication.delegate?.window
        let window = self.view.window