让自定义的独立视图具有无障碍特性

If your application contains a custom individual view with which users need to interact, you must make the view accessible. (Recall that an individual view is a view containing no other views with which users interact.)

如果应用包含一个需要与用户进行交互的自定义独立视图，开发者必须确保这个视图的无障碍特性。（回想一下，一个独立视图是指：一个视图不包含其它可与用户交互的视图。

In addition to using Interface Builder to make a custom individual view accessible, there are two programmatic ways to do this. One way is to set your custom view’s accessibility status in the code that instantiates it. The following code snippet shows how to do this:

除了使用Interface Builder构建自定义视图的无障碍特性，还可以通过两种编程方法让自定义独立视图具有无障碍特性。第一种方法是：在实例化自定义视图的代码中设置其无障碍状态。如下面的代码片段所示：

@implementation MyCustomViewController

- (id)init

{

  _view = [[[MyCustomView alloc] initWithFrame:CGRectZero] autorelease];

  [_view setIsAccessibilityElement:YES];

/* 此处设置属性*/

}

Another way is to implement the isAccessibilityElement method of the UIAccessibility protocol in the implementation of your custom subclass. The following code snippet shows how to do this:

另一种方法是在您的自定义子类实现中，UIAccessibility协议中使用isAccessibilityElement。如下面的代码片段所示：

@implementation MyCustomView

  /*此处使用属性方法 */

- (BOOL)isAccessibilityElement

{

   return YES;

}

让自定义容器视图的内容具有无障碍特性

If your application displays a custom view that contains other elements with which users interact, you need to make the contained elements separately accessible. At the same time, you need to make sure that the container view itself is not accessible. The reason is that users interact with the contents of the container, not with the container itself.

如果应用中展示了一个自定义视图，包含其他与用户交互的元素，则需要让包含元素分别具有无障碍特性。同时，开发者必须让容器视图本身不再具有无障碍特性，因为用户是与容器中的内容进行交互，不是和容器本身交互。

To accomplish this, your custom container view should implement the UIAccessibilityContainer protocol. This protocol defines methods that make the contained elements available in an array.

为此，自定义的容器视图应该实现UIAccessibilityContainer协议。这个协议会定义一些方法让被包含元素存放于一个数组中。

The following code snippet shows the partial implementation of a custom container view. Note that this container view creates the array of accessible elements only when methods of the UIAccessibilityContainer protocol are called. As a result, if iPhone accessibility is not currently active, the array is not created.

如下代码片段展示了一个自定义容器视图的部分实现。注意，这个容器视图只会在调用UIAccessibilityContainer协议时，才会创建无障碍元素数组。因此，如果iPhone的无障碍状态并没有被激活，那就不会创建该数组。

表 2-1  实现自定义容器中的内容做为独立的无障碍元素

@implementation MultiFacetedView

- (NSArray *)accessibleElements

{

   if ( _accessibleElements != nil )

   {

      return _accessibleElements;

   }

   _accessibleElements = [[NSMutableArray alloc] init];

   /*  创建一个无障碍元素展示第一个被包含的元素，并初始化它做为MultiFacetedView的组件*/

   UIAccessibilityElement *element1 = [[[UIAccessibilityElement alloc] initWithAccessibilityContainer:self] autorelease];

   /* 此处设置第一个包含元素的属性*/

   [_accessibleElements addObject:element1];

   /* 为第二个包含元素执行相同步骤*/

   UIAccessibilityElement *element2 = [[[UIAccessibilityElement alloc] initWithAccessibilityContainer:self] autorelease];

   /*此处设置第二个包含元素的属性*/

   [_accessibleElements addObject:element2];

   return _accessibleElements;

}

/* 容器本身并不具有无障碍特性，所以MultFacetedView在isAccessiblityElement中应该返回NO*/

- (BOOL)isAccessibilityElement

{

   return NO;

}

/* 如下方法实施UIAccessibilityContainer协议 */

- (NSInteger)accessibilityElementCount

{

   return [[self accessibleElements] count];

}

- (id)accessibilityElementAtIndex:(NSInteger)index

{

   return [[self accessibleElements] objectAtIndex:index];

}

- (NSInteger)indexOfAccessibilityElement:(id)element

{

   return [[self accessibleElements] indexOfObject:element];

}

@end

优化默认属性信息

As part of the built-in accessibility of standard UIKit controls and views, iOS also provides default attribute information that describes these elements to VoiceOver users. In most cases, this information is appropriate for applications that use the standard controls and views. However, there might be times when supplying custom attribute information can enhance a VoiceOver user’s experience with your application:

作为标准UIKit控件和视图内建无障碍特性的一部分，iOS也为这些元素提供了默认属性信息，这些信息可以向VoiceOver用户描述这些元素。大多数情况下，应用如果使用标准控件和视图，这种信息是合适的。但是，自定义属性信息可以增强VoiceOver用户的体验:

• If you use a standard UIKit control or view that displays a system-provided icon or title, first make sure you’re using it in accordance with its intended purpose (see iOS Human Interface Guidelines for more information). Then, decide whether the default label attribute accurately conveys the result of using that control or view in your application. If not, consider providing a hint attribute.

  如果用一个标准UIKit控件和视图显示系统提供的图标和标题，开发者首先需要确认是以预期的目的使用它（请参阅“iOS人机界面指南”了解更多信息）。然后认真考虑，在应用中，默认的标签属性是否准确地传达结果，如果没有，考虑提供一个提示属性。

  For example, if you place an Add button in your navigation bar by using the system-provided Add (+) icon in a UIBarButtonItem object, you get the default label attribute, Add, automatically. If it’s always obvious which item the user is adding when they activate this button, there’s no need to provide a hint attribute. But if there might be confusion, you should consider providing a custom hint that describes the result of using that control in your application, such as "Adds an account" or "Adds a comment."

  举例来说，如果在UIBarButtonItem对象中，开发者使用系统提供的加（+）图标，在导航栏中放置一个添加按钮，它会自动包含一个默认的标签属性：添加。如果用户可以明确地知道每次点击这个按钮会添加哪个项目，那就不需要提供提示属性。但是如果可能产生误解，开发者应该在应用中提供一个自定义的提示，用以描述使用该按钮的效果，比如“添加一个账户”或者“添加一个评论”。

• If you display a custom icon or image in a standard UIKit view, such as a UIButton object, you need to supply a custom label attribute that describes it.

  如果您在标签的UIKit视图中显示一个自定义的图标或者图像，比如UIBarButtonItem对象，需要提供一个自定义的标签属性用以描述它。

制作有用的标签和提示

When VoiceOver users run your application, they rely on the descriptions VoiceOver speaks to understand what your application does and how to use it. Because these descriptions represent the bulk of the VoiceOver user’s experience with your application it’s essential that they be as accurate and helpful as possible. The guidelines in this section help you create labels and hints that will make your application easy and enjoyable for people with disabilities to use.

当VoiceOver用户使用应用时，他们依赖VoiceOver的描述了解应用的作用以及如何使用，由于这些描述代表了大量的VoiceOver用户对于应用的体验，所以有必要尽可能让其准确有用。该指南会帮助开发者创建有用的标签和提示，让应用对于残障人士来说更加简单易用。

定义恰当的特质

The traits attribute contains one or more individual traits that, taken together, describe the behavior of an accessible user interface element. Because some individual traits can be combined to describe a single element, the element’s behavior can be precisely characterized.

特质属性包含一个或者多个独立特质，共同描述一个无障碍用户界面元素的行为。由于一些独立的特性可以组合起来一起描述一个单独元素，因此一个元素的行为可以被准确地表述。

A standard UIKit control, such as a button or text field, provides default content in the traits attribute. If you use only standard UIKit controls in your application (and do not customize their behavior in any way), you do not have to make any changes to the traits attribute of these controls.

一个标准的UIKit控件，如一个按钮或者文本域，在特质属性中会提供默认的内容。如果在应用中仅用标准UIKit控件（特指没有用任何方式自定义其行为），这些控件的特质属性不会有任何变化。

If you customize the behavior of a standard control, you might need to combine a new trait with the control’s default traits. If you create a custom control or view, you need to provide content for the element’s traits attribute.

如果是自定义行为的标准控件，开发者可能需要将某个新的特质与该控件默认的特质组合。如果创建自定义的控件视图，开发者需要提供该元素特质属性的内容。

The UI Accessibility programming interface defines 12 individual traits, some of which can be combined. Some traits characterize an element by identifying its behavior with the behavior of a particular type of control (such as a button) or type of object (such as an image). Other traits characterize an element by describing a specific behavior the element can exhibit, such the ability to play sound.

UI无障碍编程接口定义了12个独立的特质，其中某些是可以被组合的。某些特质是通过特定控件类型的行为标识一个元素（如按钮）或者对象类型（如图像）。其它特质通过描述特定元素的展示行为标识元素，如播放声音的功能。

You use the following traits to characterize elements in your application:

如下的特质可用于在应用中标识元素：

• 按钮(Button)

• 链接(Link)

• 搜索域(Search Field)

• 键盘按键(Keyboard Key)

• 静态文本(Static Text)

• 图像(Image)

• 播放声音(Plays Sound)

• 选中(Selected)

• 总结元素(Summary Element)

• 常态更新(Updates Frequently)

• 不可用(Not Enabled)

• 空(None)

In general, traits that correspond to controls can successfully be combined with traits that describe behaviors. For example, you might combine the Button trait with the Plays Sound trait to characterize a custom control that behaves like a button and plays sound when it is tapped.

通常，控件相对应特质能够结合描述行为的特质，例如，“按钮”特质可能和“播放音乐”特质用以表述一个自定义控件，其表象是一个按钮，点击即可播放音乐。

For the most part, you should consider the traits that correspond to particular controls, specifically, the Button, Link, Search Field, and Keyboard Key traits, to be mutually exclusive. That is, you should not use more than one of these traits to characterize an element in your application. Instead, think about which one of these four traits corresponds most closely to the element in your application. Then, if your element has additional behaviors, you can combine the first trait with one of the behavioral traits.

大多数情况下，应该考虑特质对应特定控件，尤其是，按钮、链接、搜索域、键盘键的特质，是互斥的。这时，不应该使用超过一个特质去表述应用中的某个元素，如果此元素有其它行为，可以将第一个特质和某一个行为特质结合。

For example, suppose you display an image in your application that responds to a user’s tap by opening a link in Safari on iPhone. You could characterize this element by combining the Image and Link traits. Another example is a keyboard key that modifies other keyboard keys when it is tapped. You could characterize this element by combining the Keyboard Key and Selected traits.

例如，假设显示在应用中的一个图像，其响应的是，当用户点击时会在iPhone中的Safari打开一个链接，开发者应该通过结合图像和链接的特质表述该元素。另如，一个键盘键当点击时修改其它键盘键，开发者应该通过结合键盘键和选中的特质标识该元素。

To see some examples of how traits characterize controls, you can use Accessibility Inspector to see the default traits that are set on the standard controls. For information on how to use Accessibility Inspector, read Debug Accessibility in iOS Simulator with the Accessibility Inspector.

了解如何标识控件的案例，可以用Accessibility Inspector看在标准控件中已被设定的默认特质。更多关于如何使用Accessibility Inspector，请参阅通过Accessibility Inspector在iOS Simulator无障碍排错。

在Interface Builder中自定义属性信息

When you install iOS SDK 3.0, you get a version of Interface Builder that includes features that help you make your application accessible. If your application contains standard UIKit controls and views, you might be able to do all your accessibility work in Interface Builder.

安装iOS SDK 3.0后，获得的Interface Builder版本包含帮助应用达到无障碍特性的功能。如果应用包含标准UIKit的控件和视图，可通过Interface Builder做所有的无障碍工作。

Using Interface Builder, you can set an element’s accessibility status and provide custom content for the label, hint, and traits attributes. To do this, select the user interface element in your nib file and open the Identity inspector. Reveal the Accessibility section in the inspector and you should see something like Figure 2-1:

使用Interface Builder，可以设置元素的无障碍状态，并且为标签(label)和特质(traits)属性提供自定义内容。为此，在nib文件中选择用户界面元素，并且打开Identity inspector，在inspector中的Accessibility处，应该可以看到如图2-1所示内容：

As you can see in Figure 2-1, the standard text field used in the nib file is accessible by default and includes default information for the label, hint, and traits attributes. (Note that, for a text field that displays placeholder text, the default label is the placeholder text.) You can change any of these default values by supplying new information in the Identify inspector, as shown in Figure 2-2. (Figure 2-2 also shows how Accessibility Inspector displays the accessibility information for the text field. See Debug Accessibility in iOS Simulator with the Accessibility Inspector to learn about Accessibility Inspector.)

如图2-1所示，用于nib文件中的标准文本域默认是无障碍的，并且标签(label)、提示(hint)、特质(traits)的属性中包含默认的信息，（注意，文本域显示占位符文本，默认的标签就是占位符文本），在Identify inspector中可以提供新的信息改变任何默认值。如在图2-2所示，（图2-2显示的也是Accessibility Inspector如何显示文本域中的无障碍信息。参阅通过Accessibility Inspector在iOS Simulator无障碍排错）。

编程化处理自定义属性信息

If you prefer, you can supply custom information for attributes programmatically. You might want to do this if you’re not using Interface Builder at all or if you generate your views in code instead of using Interface Builder.

如果愿意，开发者可以通过编程为属性提供自定义信息。如果开发者完全不用Interface Builder或者更喜欢在代码中生成视图，这可能是开发者想用的方法。

As described in Make Custom Individual Views Accessible, you can set accessibility information in the implementation of your view subclass or in the code that instantiates the view. Both techniques are valid, but there is one reason why you might want to implement attribute methods in your subclass instead of setting attributes in the instantiation code: If your view displays data that is dynamic or that changes frequently, such as the time of day, you should implement the subclass methods to return fresh data as needed. For those situations, if you only set attributes when you instantiate the subclass, the returned data is likely to be out of date.

在让自定义的独立视图具有无障碍特性中介绍过，开发者可以在视图子类或在代码里实例化视图设置无障碍信息。两种方法都是有效的，但是为什么开发者可能需要在子类中实现属性方法而不是通过代码实例化实现，原因是：如果显示数据是动态的，或者频繁改变，如日期，开发者应该实现子类方法返回需要的刷新数据。在这些情况下，如果仅在实例化子类时设置属性，返回的数据可能是过期的。

The code snippets in this section build on those in Make Custom Individual Views Accessible, by including some of the attribute-specific methods. For example, if you want to implement accessibility methods in your subclass, you would write code similar to that in Listing 2-2.

此章节的代码片段是基于让自定义的独立视图具有无障碍特性，包含一些属性特有的方法。例如：如果开发者想在子类中实现无障碍方法，将会用到类似表2-2的代码：

表 2-2  在自定义子类实现中提供属性信息

@implementation MyCustomView

- (BOOL)isAccessibilityElement

{

   return YES;

}

- (NSString *)accessibilityLabel

{

   return NSLocalizedString(@"MyCustomView.label", nil);

}

/* 这个自定义控件的表像为一个按钮*/

- (UIAccessibilityTraits)accessibilityTraits

{

   return UIAccessibilityTraitButton;

}

- (NSString *)accessibilityHint

{

   return NSLocalizedString(@"MyCustomView.hint", nil);

}

@end

If you want to use the property-setting methods of the UIAccessibility protocol in the code that instantiates your custom view, you can write code similar to that in Listing 2-3.

如果您要在代码中使用UIAccessibility协议的属性设定方法，实例化自定义视图，将会用到类似于表2-3中的代码。

表 2-3  在代码中提供属性信息，实例化自定义的子类对象

@implementation MyCustomViewController

- (id)init

{

  _view = [[MyCustomView alloc] initWithFrame:CGRectZero];

  [_view setIsAccessibilityElement:YES];

  [_view setAccessibilityTraits:UIAccessibilityTraitButton];

  [_view setAccessibilityLabel:NSLocalizedString(@"view.label", nil)];

  [_view setAccessibilityHint:NSLocalizedString(@"view.hint", nil)];

}