arc : automatic reference counting

ut: unit test

delegate:

.m 可以有私有的方法

UITableViewDataSource:连接表视图和数据

UITableViewDelegate: 处理UItableView的表现

IBOutlet 指示符

File's Owner represents the object that loaded the nib file from disk.

First Responder is the object with which the user is currently interacting.

Separation of Concerns (SoC,关注点分离)