Swift 记录 --- 懒加载(lazy)

1.简单写法

private lazy var imageArr: NSMutableArray  = NSMutableArray() 

private lazy var dataArr: NSMutableArray  = NSMutableArray()

2.闭包

private lazy var customView: UIView = { 
    let customView = UIView(frame:CGRectMake(0,0,W,H)) 
    customView.backgroundColor = UIColor.whiteColor()
    customView.alpha = 0.0
    return customView 
}()