Applications built for Android are more accessible to users with visual, physical or age-related limitations when those users activate accessibility services and features on a device. These services make your application more accessible even if you do not make any accessibility changes to your code. However, there are steps you should take to optimize the accessibility of your application and ensure a pleasant experience for all your users.
Making sure your application is accessible to all users requires only a few steps, particularly when you create your user interface with the components provided by the Android framework. If you use only the standard components for your application, the steps are:
If you build custom controls that extend the {@link android.view.View} class, you must complete some additional work to make sure your components are accessible. This document discusses how to make custom view controls compatible with accessibility services.
Note: The implementation steps in this document describe the requirements for making your application accessible for users with blindness or low-vision. Be sure to review the requirements for serving users who are deaf and hard of hearing in the Accessibility Developer Checklist
.Many user interface controls depend on visual cues to indicate their meaning and usage. For example, a note-taking application might use an {@link android.widget.ImageButton} with a picture of a plus sign to indicate that the user can add a new note. An {@link android.widget.EditText} component may have a label near it that indicates its purpose. A user with impaired vision can't see these cues well enough to follow them, which makes them useless.
You can make these controls more accessible with the {@code android:contentDescription} XML layout attribute. The text in this attribute does not appear on screen, but if the user enables accessibility services that provide audible prompts, then when the user navigates to that control, the text is spoken.
For this reason, set the {@code android:contentDescription} attribute for every {@link android.widget.ImageButton}, {@link android.widget.ImageView}, {@link android.widget.CheckBox} in your application's user interface, and add descriptions to any other input controls that might require additional information for users who are not able to see it.
For example, the following {@link android.widget.ImageButton} sets the content description for the plus button to the {@code add_note} string resource, which could be defined as “Add note" for an English language interface:
<ImageButton
android:id=”@+id/add_note_button”
android:src=”@drawable/add_note”
android:contentDescription=”@string/add_note”/>
By including the description, an accessibility service that provides spoken feedback can announce "Add note" when a user moves focus to this button or hovers over it.
Note: For {@link android.widget.EditText} fields, provide an android:hint attribute instead of a content description, to help users understand what content is expected when the text field is empty. When the field is filled, TalkBack reads the entered content to the user, instead of the hint text.
Focus navigation allows users with disabilities to step through user interface controls using a directional controller. Directional controllers can be physical, such as a trackball, directional pad (D-pad) or arrow keys, or virtual, such as the Eyes-Free Keyboard, or the gestures navigation mode available in Android 4.1 and higher. Directional controllers are a primary means of navigation for many Android users.
To ensure that users can navigate your application using only a directional controller, verify that all user interface (UI) input controls in your application can be reached and activated without using the touchscreen. You should also verify that clicking with the center button (or OK button) of a directional controller has the same effect as touching a control that already has focus. For information on testing directional controls, see Testing focus navigation.
A user interface element is reachable using directional controls when its {@code android:focusable} attribute is set to {@code true}. This setting allows users to focus on the element using the directional controls and then interact with it. The user interface controls provided by the Android framework are focusable by default and visually indicate focus by changing the control’s appearance.
Android provides several APIs that let you control whether a user interface control is focusable and even request that a control be given focus:
If a view is not focusable by default, you can make it focusable in your layout file by setting the {@code android:focusable} attribute to {@code true} or by calling the its {@link android.view.View#setFocusable setFocusable()} method.
When users navigate in any direction using directional controls, focus is passed from one user interface element (view) to another, as determined by the focus order. This order is based on an algorithm that finds the nearest neighbor in a given direction. In rare cases, the algorithm may not match the order that you intended or may not be logical for users. In these situations, you can provide explicit overrides to the ordering using the following XML attributes in your layout file:
The following example XML layout shows two focusable user interface elements where the {@code android:nextFocusDown} and {@code android:nextFocusUp} attributes have been explicitly set. The {@link android.widget.TextView} is located to the right of the {@link android.widget.EditText}. However, since these properties have been set, the {@link android.widget.TextView} element can now be reached by pressing the down arrow when focus is on the {@link android.widget.EditText} element:
<LinearLayout android:orientation="horizontal"
... >
<EditText android:id="@+id/edit"
android:nextFocusDown=”@+id/text”
... />
<TextView android:id="@+id/text"
android:focusable=”true”
android:text="Hello, I am a focusable TextView"
android:nextFocusUp=”@id/edit”
... />
</LinearLayout>
When modifying focus order, be sure that the navigation works as expected in all directions from each user interface control and when navigating in reverse (to get back to where you came from).
Note: You can modify the focus order of user interface components at runtime, using methods such as {@link android.view.View#setNextFocusDownId setNextFocusDownId()} and {@link android.view.View#setNextFocusRightId setNextFocusRightId()}.
If your application requires a custom view component, you must do some additional work to ensure that your custom view is accessible. These are the main tasks for ensuring the accessibility of your view:
On most devices, clicking a view using a directional controller sends a {@link android.view.KeyEvent} with {@link android.view.KeyEvent#KEYCODE_DPAD_CENTER} to the view currently in focus. All standard Android views already handle {@link android.view.KeyEvent#KEYCODE_DPAD_CENTER} appropriately. When building a custom {@link android.view.View} control, make sure this event has the same effect as touching the view on the touchscreen.
Your custom control should also treat the {@link android.view.KeyEvent#KEYCODE_ENTER} event the same as {@link android.view.KeyEvent#KEYCODE_DPAD_CENTER}. This approach makes interaction from a full keyboard much easier for users.
Accessibility events are messages about users interaction with visual interface components in your application. These messages are handled by Accessibility Services, which use the information in these events to produce supplemental feedback and prompts. In Android 4.0 (API Level 14) and higher, the methods for generating accessibility events have been expanded to provide more detailed information than the {@link android.view.accessibility.AccessibilityEventSource} interface introduced in Android 1.6 (API Level 4). The expanded accessibility methods are part of the {@link android.view.View} class as well as the {@link android.view.View.AccessibilityDelegate} class. The methods are as follows:
Note: Modifying additional attributes beyond the text within this method potentially overwrites properties set by other methods. While you can modify attributes of the accessibility event with this method, you should limit these changes to text content, and use the {@link android.view.View#onInitializeAccessibilityEvent onInitializeAccessibilityEvent()} method to modify other properties of the event.
Note: If your implementation of this event completely overrides the output text without allowing other parts of your layout to modify its content, then do not call the super implementation of this method in your code.
In order to support these accessibility methods for a custom view, you should take one of the following approaches:
In either case, you should implement the following accessibility methods for your custom view class:
For more information about implementing these methods, see Populating Accessibility Events.
Depending on the specifics of your custom view, it may need to send {@link android.view.accessibility.AccessibilityEvent} objects at a different times or for events not handled by the default implementation. The {@link android.view.View} class provides a default implementation for these event types:
Note: Hover events are associated with the Explore by Touch feature, which uses these events as triggers for providing audible prompts for user interface elements.
In general, you should send an {@link android.view.accessibility.AccessibilityEvent} whenever the content of your custom view changes. For example, if you are implementing a custom slider bar that allows a user to select a numeric value by pressing the left or right arrows, your custom view should emit an event of type {@link android.view.accessibility.AccessibilityEvent#TYPE_VIEW_TEXT_CHANGED} whenever the slider value changes. The following sample code demonstrates the use of the {@link android.view.accessibility.AccessibilityEventSource#sendAccessibilityEvent sendAccessibilityEvent()} method to report this event.
@Override
public boolean onKeyUp (int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_DPAD_LEFT) {
mCurrentValue--;
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_TEXT_CHANGED);
return true;
}
...
}
Each {@link android.view.accessibility.AccessibilityEvent} has a set of required properties that describe the current state of the view. These properties include things such as the view’s class name, content description and checked state. The specific properties required for each event type are described in the {@link android.view.accessibility.AccessibilityEvent} reference documentation. The {@link android.view.View} implementation provides default values for these properties. Many of these values, including the class name and event timestamp, are provided automatically. If you are creating a custom view component, you must provide some information about the content and characteristics of the view. This information may be as simple as a button label, but may also include additional state information that you want to add to the event.
The minimum requirement for providing information to accessibility services with a custom view is to implement {@link android.view.View#dispatchPopulateAccessibilityEvent dispatchPopulateAccessibilityEvent()}. This method is called by the system to request information for an {@link android.view.accessibility.AccessibilityEvent} and makes your custom view compatible with accessibility services on Android 1.6 (API Level 4) and higher. The following example code demonstrates a basic implementation of this method.
@Override
public void dispatchPopulateAccessibilityEvent(AccessibilityEvent event) {
super.dispatchPopulateAccessibilityEvent(event);
// Call the super implementation to populate its text to the event, which
// calls onPopulateAccessibilityEvent() on API Level 14 and up.
// In case this is running on a API revision earlier that 14, check
// the text content of the event and add an appropriate text
// description for this custom view:
CharSequence text = getText();
if (!TextUtils.isEmpty(text)) {
event.getText().add(text);
}
}
For Android 4.0 (API Level 14) and higher, use the {@link android.view.View#onPopulateAccessibilityEvent onPopulateAccessibilityEvent()} and {@link android.view.View#onInitializeAccessibilityEvent onInitializeAccessibilityEvent()} methods to populate or modify the information in an {@link android.view.accessibility.AccessibilityEvent}. Use the {@link android.view.View#onPopulateAccessibilityEvent onPopulateAccessibilityEvent()} method specifically for adding or modifying the text content of the event, which is turned into audible prompts by accessibility services such as TalkBack. Use the {@link android.view.View#onInitializeAccessibilityEvent onInitializeAccessibilityEvent()} method for populating additional information about the event, such as the selection state of the view.
In addition, implement the {@link android.view.View#onInitializeAccessibilityNodeInfo onInitializeAccessibilityNodeInfo()} method. The {@link android.view.accessibility.AccessibilityNodeInfo} objects populated by this method are used by accessibility services to investigate the view hierarchy that generated an accessibility event after receiving that event, to obtain a more detailed context information and provide appropriate feedback to users.
The example code below shows how override these three methods by using {@link android.support.v4.view.ViewCompat#setAccessibilityDelegate ViewCompat.setAccessibilityDelegate()}. Note that this sample code requires that the Android Support Library for API Level 4 (revision 5 or higher) is added to your project.
ViewCompat.setAccessibilityDelegate(new AccessibilityDelegateCompat() {
@Override
public void onPopulateAccessibilityEvent(View host, AccessibilityEvent event) {
super.onPopulateAccessibilityEvent(host, event);
// We call the super implementation to populate its text for the
// event. Then we add our text not present in a super class.
// Very often you only need to add the text for the custom view.
CharSequence text = getText();
if (!TextUtils.isEmpty(text)) {
event.getText().add(text);
}
}
@Override
public void onInitializeAccessibilityEvent(View host, AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(host, event);
// We call the super implementation to let super classes
// set appropriate event properties. Then we add the new property
// (checked) which is not supported by a super class.
event.setChecked(isChecked());
}
@Override
public void onInitializeAccessibilityNodeInfo(View host,
AccessibilityNodeInfoCompat info) {
super.onInitializeAccessibilityNodeInfo(host, info);
// We call the super implementation to let super classes set
// appropriate info properties. Then we add our properties
// (checkable and checked) which are not supported by a super class.
info.setCheckable(true);
info.setChecked(isChecked());
// Quite often you only need to add the text for the custom view.
CharSequence text = getText();
if (!TextUtils.isEmpty(text)) {
info.setText(text);
}
}
}
In applications targeting Android 4.0 (API Level 14) and higher, you can implement these methods directly in your custom view class. For another example of this approach, see the Android Support Library (revision 5 or higher) sample {@code AccessibilityDelegateSupportActivity} in ({@code <sdk>/extras/android/support/v4/samples/Support4Demos/}).
Note: You may find information on implementing accessibility for custom views written prior to Android 4.0 that describes the use of the {@link android.view.View#dispatchPopulateAccessibilityEvent dispatchPopulateAccessibilityEvent()} method for populating AccessibilityEvents. As of the Android 4.0 release, however, the recommended approach is to use the {@link android.view.View#onPopulateAccessibilityEvent onPopulateAccessibilityEvent()} and {@link android.view.View#onInitializeAccessibilityEvent onInitializeAccessibilityEvent()} methods.
In Android 4.0 (API Level 14), the framework was enhanced to allow accessibility services to inspect the containing view hierarchy of a user interface component that generates an accessibility event. This enhancement allows accessibility services to provide a much richer set of contextual information with which to aid users.
There are some cases where accessibility services cannot get adequate information from the view hierarchy. An example of this is a custom interface control that has two or more separately clickable areas, such as a calendar control. In this case, the services cannot get adequate information because the clickable subsections are not part of the view hierarchy.
Figure 1. A custom calendar view with selectable day elements.
In the example shown in Figure 1, the entire calendar is implemented as a single view, so if you do not do anything else, accessibility services do not receive enough information about the content of the view and the user's selection within the view. For example, if a user clicks on the day containing 17, the accessibility framework only receives the description information for the whole calendar control. In this case, the TalkBack accessibility service would simply announce "Calendar" or, only slightly better, "April Calendar" and the user would be left to wonder what day was selected.
To provide adequate context information for accessibility services in situations like this, the framework provides a way to specify a virtual view hierarchy. A virtual view hierarchy is a way for application developers to provide a complementary view hierarchy to accessibility services that more closely matches the actual information on screen. This approach allows accessibility services to provide more useful context information to users.
Another situation where a virtual view hierarchy may be needed is a user interface containing a set of controls (views) that have closely related functions, where an action on one control affects the contents of one or more elements, such as a number picker with separate up and down buttons. In this case, accessibility services cannot get adequate information because action on one control changes content in another and the relationship of those controls may not be apparent to the service. To handle this situation, group the related controls with a containing view and provide a virtual view hierarchy from this container to clearly represent the information and behavior provided by the controls.
In order to provide a virtual view hierarchy for a view, override the {@link android.view.View#getAccessibilityNodeProvider} method in your custom view or view group and return an implementation of {@link android.view.accessibility.AccessibilityNodeProvider}. For an example implementation of this accessibility feature, see {@code AccessibilityNodeProviderActivity} in the ApiDemos sample project. You can implement a virtual view hierarchy that is compatible with Android 1.6 and later by using the Support Library with the {@link android.support.v4.view.ViewCompat#getAccessibilityNodeProvider ViewCompat.getAccessibilityNodeProvider()} method and providing an implementation with {@link android.support.v4.view.accessibility.AccessibilityNodeProviderCompat}.
Custom view controls may require non-standard touch event behavior. For example, a custom control may use the {@link android.view.View#onTouchEvent} listener method to detect the {@link android.view.MotionEvent#ACTION_DOWN} and {@link android.view.MotionEvent#ACTION_UP} events and trigger a special click event. In order to maintain compatibility with accessibility services, the code that handles this custom click event must do the following:
To handle these requirements in an efficient way, your code should override the {@link android.view.View#performClick} method, which must call the super implementation of this method and then execute whatever actions are required by the click event. When the custom click action is detected, that code should then call your {@code performClick()} method. The following code example demonstrates this pattern.
class CustomTouchView extends View {
public CustomTouchView(Context context) {
super(context);
}
boolean mDownTouch = false;
@Override
public boolean onTouchEvent(MotionEvent event) {
super.onTouchEvent(event);
// Listening for the down and up touch events
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mDownTouch = true;
return true;
case MotionEvent.ACTION_UP:
if (mDownTouch) {
mDownTouch = false;
performClick(); // Call this method to handle the response, and
// thereby enable accessibility services to
// perform this action for a user who cannot
// click the touchscreen.
return true;
}
}
return false; // Return false for other touch events
}
@Override
public boolean performClick() {
// Calls the super implementation, which generates an AccessibilityEvent
// and calls the onClick() listener on the view, if any
super.performClick();
// Handle the action for the custom click here
return true;
}
}
The pattern shown above makes sure that the custom click event is compatible with accessibility services by using the {@link android.view.View#performClick} method to both generate an accessibility event and provide an entry point for accessibility services to act on behalf of a user to perform this custom click event.
Note: If your custom view has distinct clickable regions, such as a custom calendar view, you must implement a virtual view hierarchy by overriding {@link android.view.View#getAccessibilityNodeProvider} in your custom view in order to be compatible with accessibility services.
Testing the accessibility of your application is an important part of ensuring your users have a great experience. You can test the most important accessibility features by using your application with audible feedback enabled and navigating within your application using only directional controls. For more information on testing accessibility in your application, see the Accessibility Testing Checklist.