懒加载

import UIKit
 
class ViewController: UIViewController {
    // 只有外界访问到listData的时候才会去执行闭包,然后将闭包的返回值赋值给listData
    // 注意: 一定要记住闭包后面需要写上(),代表执行闭包
    lazy var listData: [String]? = {
        ()->[String]
        in
        print("----")
        return ["longshao","guangzhou",0)">"beijing",0)">"shenzhen"]
        }()
 
    // 开发中这样写
    lazy var listData2: [String]? = {
        print("shenzhen"]
    }()
 
    lazy var listData3: [String]? = self.test()
    func test() -> [String]
    {
        print("+++")
        "lnj1",0)">"lmj1",0)">"why1",0)">"wsz1"]
    }
 
    override func touchesBegan(touches: Set<UITouch>,withEvent event: UIEvent?) {
        print(listData!)
        print(listData)
        print(listData)
 
        print("++++++++++++++++++++++++++++")
 
        print(listData2)
        print(listData2)
        print(listData2)
 
        print("++++++++++++++++++++++++++++")
 
        print(listData3)
        print(listData3)
        print(listData3)
    }
}