Swift 单例与懒加载

//懒加载就是在闭包中创建对象,并且只加载一次
lazy var btn : UIButton = { //() -> UIButton in

let button = UIButton(frame: CGRect(x: 0, y: 0, width: 20, height: 20))

return button
} ()
//懒加载数据
lazy var lable : UILabel = {

let lable1  = UILabel()
return lable1
} ()

//单例
class NetTools: NSObject {
var urlString : String?
//简单的单例
static let singNetTool : NetTools = NetTools()
//复杂的单例 也是一个闭包
var singsss: String?
static let singNetTools : NetTools = { //() -> NetTools in

let singa = NetTools()
singa.urlString = "http://www.baidu.com"
return singa
} ()
}