To programmaictlly change the content of app, we need to contect storyboard to a view controller. To do that, we need to create new file call it 'ProductViewController', subclass should UIViewController: Delete some uncessary code, the remain code sh
1. 定义变量 var name = "***" 定义常量 let name ="*****" 2. swift 变量类型 String, Int, Float, Double 3. swift 逻辑操作符 && , ||, ! 4. swift 关系运算符 ==, !=, >=, <= 5. swift storyboard界面元素跟code绑定,右键(button , label什么的),左键按住划线到view, 选择对应