The UI Accessibility Programming Interface | UI无障碍编程接口

The UI Accessibility programming interface consists of two informal protocols, one class, a function, and a handful of constants:

UI无障碍编程接口是由两个非正式协议、一个类、一个函数，以及少数常量构成。

• The UIAccessibility informal protocol. Objects that implement the UIAccessibility protocol report their accessibility status (that is, whether they are accessible) and supply descriptive information about themselves. Standard UIKit controls and views implement the UIAccessibility protocol by default.

  UIAccessibility非正式协议：实现 UIAccessibility协议的对象，可以报告无障碍状态（即他们是否是可访问的），并且提供其自身的描述信息。 标准UIKit控件和视图默认已实现了UIAccessibility协议。

• The UIAccessibilityContainer informal protocol. This protocol allows a subclass of UIView to make some or all of the objects it contains accessible as separate elements. This is particularly useful when the objects contained in such a view are not themselves subclasses of UIView and, for this reason, are not automatically accessible.

  UIAccessibilityContainer非正式协议：此协议允许UIView的子类作为分离元素，具有无障碍特性构建部分或者全部对象。当对象包含在视图中，其本身又不是UIView的子类，导致不能被自动地无障碍访问，此时，该协议非常有用。

• The UIAccessibilityElement class. This class defines an object that can be returned through the UIAccessibilityContainer protocol. You can create an instance of UIAccessibilityElement to represent an item that isn’t automatically accessible, such as an object that does not inherit from UIView, or an object that does not exist.

  UIAccessibilityElement类：这个类定义了一个能够通过UIAccessibilityContainer协议返回的对象。当一个元素不是自动地无障碍访问，您可以通过创建一个UIAccessibilityElement实例以展示它，例如一个并非从UIView继承的对象，或者一个不存在的对象。

• The UIAccessibilityConstants.h header file. This header file defines the constants that describe the traits that an accessibility element can exhibit and the notifications that an application can post.

  UIAccessibilityConstants.h头文件：这个头文件定义了某些常量，这些常量即可以描述一个可展示的无障碍元素的特征，也可以描述应用发布的通知。

Accessibility Attributes | 无障碍属性

The attributes that describe an accessible user interface element make up the core of the UI Accessibility API. VoiceOver supplies attribute information to users when they access or interact with a control or view.

用来描述无障碍用户界面元素的属性也是UI Accessibility API的核心构成。当用户访问控件和视图，或与之交互时，VoiceOver会将无障碍属性信息告知给用户。

Attributes are also the components of the programming interface that you’re most likely to use. This is because attributes encapsulate the information that differentiates one control or view from another. For standard UIKit controls and views, you might just need to ensure that the default attribute information is appropriate for your application; for custom controls and views, you might have to supply most of the attribute information.

属性是您最有可能用到的编程接口组件。因为它封装了用于区分不同控件和视图的信息。标准UIKit控件和视图，只需确保应用中默认的属性是适当的。对于自定义的控件和视图来说，可能需要提供大部分的属性信息。

The UI Accessibility programming interface defines the following attributes:

UI Accessibility编程接口定义了如下属性：

• Label. A short, localized word or phrase that succinctly describes the control or view, but does not identify the element’s type. Examples are “Add” or “Play.”

  Label（标签）：一个简短的本地化词语或短语，用于简洁地描述控件或者视图，但是不用来定义元素类型。例如“添加”或“播放”。

• Traits. A combination of one or more individual traits, each of which describes a single aspect of an element’s state, behavior, or usage. For example, an element that behaves like a keyboard key and that is currently selected can be characterized by the combination of the Keyboard Key and Selected traits.

  Traits (特质)：一个或多个独立特质的组合。每个特质描述元素中状态、行为、用途的某一方面。例如，某个元素的表象为键盘按键且当前被选定，这个元素就有了Keyboard Key和Selected的组合特质。

• Hint. A brief, localized phrase that describes the results of an action on an element. Examples are “Adds a title” or “Opens the shopping list.”

  Hint (提示)：简要的本地化语句，用于描述某元素动作的结果，例如：“添加标题”或者“打开购物清单”。

• Frame. The frame of the element in screen coordinates, which is given by the CGRect structure that specifies an element’s screen location and size.

  Frame (框架)：元素的框架是元素在屏幕上的坐标，是由CGRect结构体提供，说明了元素的屏幕位置和大小。

• Value. The current value of an element, when the value is not represented by the label. For example, the label for a slider might be “Speed,” but its current value might be “50%.”

  Value (值)：当值无法被标签代表时，一个元素的当前值。例如，一个滑动条的标签可以是”速度”，但是它当前的值是“50%”。

Accessibility elements provide content for attributes, whether that content is supplied by default or by you. An accessibility element always provides content for the frame and label attributes. The frame attribute is required because an accessibility element must always be able to report its position in the user interface. (Note that an object that inherits from UIView includes the frame attribute by default.) The label attribute is required because it contains the name or description of the accessibility element that VoiceOver speaks.

无障碍元素需要为属性提供内容，无论这些内容是被默认提供还是由您提供。无障碍元素应该为框架和标签属性提供内容。框架属性是必须的，因为无障碍元素必须能够报告它在用户界面中的位置。（注意：一个由UIView继承的对象，默认是包含了框架属性的）。标签属性也是必须的，因为它包含了无障碍元素的名称和描述，这些是可以被VoiceOver朗读出来的。

An accessibility element is not required to provide content for the hint and traits attributes, if these attributes do not apply to the element. For example, an element that does not perform an action does not need to provide a hint.

如果某个无障碍元素，其提示和特质的属性不适用时，就无需为其提供内容。例如，某个不能触发动作的元素，不需提供提示。

An accessibility element provides information for the value attribute only when the element’s contents are changeable and cannot always be described by the label. For example, a text field that contains an email address might have the label “Email address,” but its contents depends on user input and is usually of the form “username@address.” Figure 1-1 shows some of the information VoiceOver might provide.

只有元素内容是可改变的且不能通过标签描述时，无障碍元素才为值提供信息。例如，文本域包含一个邮件地址，可能有个标签描述“邮件地址”，然而其内 容是基于用户输入的，并且内容通常的形式为“username@address”。图 1-1 展示了一些VoiceOver应该提供的信息。

VoiceOver users rely on the labels and hints they hear to help them use your application. For this reason, it’s especially important to make sure that every accessible user interface element in your application provides accurate and informative descriptions. For standard UIKit controls and views, the default attribute information is often appropriate, but you should inspect these elements to make sure. For custom controls and views, you may have to supply some or all of this information yourself. For some guidelines on how to do this, see Crafting Useful Labels and Hints.

VoiceOver用户在使用您的应用时，是依赖听觉获取标签和提示。因此，确保应用中的每一个无障碍元素提供准确全面的描述是极其重要的。标准 UIKit控件和视图的默认值信息通常是准确的，但是您还是应该检查确保正确。对于自定义控件和视图，您可能不得不亲自提供部分或者全部信息。请参看“标记好用的标签和提示”中的指导，了解如何提供这些信息。