A search bar provides an interface for text-based searches with a text box and buttons such as search and cancel. A search bar
accepts text from users, which can be used as input for a search (shown here with placeholder text). A scope bar, which is available only in conjunction with a search bar—allows users to define the scope of a search (shown here below a search bar).
search bar提供了一个带有搜索、取消button以及文本框的基于文本搜索的界面。search bar接收用户输入的文本。用这些文本来作为搜索条件进行搜索（在这里显示为占位符）。scope
bar。它仅仅能连同search bar一起显示，同意用户定义搜索范围（以下显示就是一个search bar）。
Purpose. Search bars allow users to:
-
Quickly find a value in a large collection
-
在一个大的集合里面高速查找某个值
-
Create a scope filter
-
创建一个范围过滤器
Implementation. Search
bars are implemented in the
UISearchBar class
and discussed in the UISearchBar
Class Reference.