Most iOS apps are built using components from UIKit, a programming framework that defines common interface elements. This framework lets apps achieve a consistent appearance across the system, while at the same time offering a high level of customization. UIKit elements are flexible and familiar. They’re adaptable, enabling you to design a single app that looks great on any iOS device, and they automatically update when the system introduces appearance changes. The interface elements provided by UIKit fit into three main categories:
大多数iOS app 使用 UIKit 的组件来创建。UIKit是一个编程框架，可以定义普通界面元素。这个框架让app在整个系统中外观表现一致，与此同时提供高阶的定制。UIKit 元素灵活且常见。他们适应性强，让你设计一个APP在任何iOS设备看上去都很好， 并且当系统引入外观改变时他们会自动升级。UIKit提供的界面元素适用3种主要类目：
Bars.Tell people where they are in your app, provide navigation, and may contain buttons or other elements for initiating actions and communicating information.
栏目(Bars)，提供导航，指示用户他们在哪里，也可以包含按钮或者其它触发动作的元素和交流信息。
Views.Contain the primary content people see in your app, such as text, graphics, animations, and interactive elements. Views can enable behaviors such as scrolling, insertion, deletion, and arrangement.
视图(Views)，包含用户app里看到的基本内容，如文本，图形，动画，和交互元素。视图能启用行为，如滚动，插入，删除，排序。
Controls.Initiate actions and convey information. Buttons, switches, text fields, and progress indicators are examples of controls.
控制器(Controls)，监听动作或传递信息。按钮，切换，文本输入，和进度指示都是控制器的例子。
In addition to defining the interface of iOS, UIKit defines functionality your app can adopt. Through this framework, for example, your app can respond to gestures on the touchscreen and enable features such as drawing, accessibility, and printing.
除了定义iOS的界面，UIkit 也定义了app可以采用的功能。举个例子，通过这个框架app能够在触摸屏上识别手势和启用特性 ，如绘图，存取访问和打印。
iOS tightly integrates with other programming frameworks and technologies too, such as Apple Pay, HealthKit, and ResearchKit, enabling you to design amazingly powerful apps.
iOS也紧密的集成了其它程序框架和技术，如苹果支付（Apple Pay）, 健康工具（HealthKit）,和调查工具（ResearchKit）。
