Applications built for Android are accessible to users with visual, physical or age-related disabilities when they activate accessibility features and services on a device. By default, these services make your application more accessible. However, there are further 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 is relatively easy, particularly when you use framework-provided user interface components. If you only use these standard components for your application, there are just a few steps required to ensure your application is accessible:
Developers who create custom controls that extend from the {@link android.view.View} class have some additional responsibilities for making sure their components are accessible for users. This document also discusses how to make custom view controls compatible with accessibility services.
Many user interface controls rely on visual cues to inform users of their meaning. 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. Or, an {@link android.widget.EditText} component may have a label near it that indicates its purpose. When a user with impaired vision accesses your application, these visual cues are often useless.
To provide textual information about interface controls (as an alternative to the visual cues), use the {@code android:contentDescription} attribute. The text you provide in this attribute is not visible on the screen, but if a user has enabled accessibility services that provide audible prompts, then the description in this attribute is read aloud to the user.
Set the {@code android:contentDescription} attribute for every {@link android.widget.ImageButton}, {@link android.widget.ImageView}, {@link android.widget.EditText}, {@link android.widget.CheckBox} in your application's user interface, and on 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, speech-based accessibility services 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 to help users understand what content is expected.
Focus navigation allows users with disabilities to step through user interface controls using a directional controller. Directional controllers can be physical, such as a clickable trackball, directional pad (D-pad) or arrow keys, tab key navigation with an attached keyboard or a software application, such as the Eyes-Free Keyboard, that provides an on-screen directional control.
A directional controller is a primary means of navigation for many users. Verify that all user interface (UI) controls in your application are accessible without using the touchscreen and that clicking with the center button (or OK button) of a directional controller has the same effect as touching the controls on the touchscreen. For information on testing directional controls, see Testing focus navigation.
A user interface element is accessible 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:
When working with a view that is not focusable by default, you can make it focusable from the XML layout file by setting the {@code android:focusable} attribute to {@code true} or by using the {@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 ordering. The ordering of the focus movement is based on an algorithm that finds the nearest neighbor in a given direction. In rare cases, the default algorithm may not match the order that you intended for your UI. In these situations, you can provide explicit overrides to the ordering using the following XML attributes in the 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 when users have enabled accessibility services. As of Android 4.0 (API Level 14) and higher, the methods for generating accessibility events have been expanded to provide more detailed information beyond 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. So, while you are able modify attributes of the accessibility event with this method, you should limit these changes to text content only and use the {@link android.view.View#onInitializeAccessibilityEvent onInitializeAccessibilityEvent()} method to modify other properties of the event.
Note: If your implementation of this event calls for completely overiding 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);
}
}
On Android 4.0 (API Level 14) and higher, the {@link android.view.View#onPopulateAccessibilityEvent onPopulateAccessibilityEvent()} and {@link android.view.View#onInitializeAccessibilityEvent onInitializeAccessibilityEvent()} methods are the recommended way 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, you should also implement the {@link android.view.View#onInitializeAccessibilityNodeInfo onInitializeAccessibilityNodeInfo()} method. {@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);
}
}
}
On applications targeting Android 4.0 (API Level 14) and higher, these methods can be implemented 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.
Testing the accessibility of your application is an important part of ensuring your users have a great experience. You can test the most important parts of accessibility by testing your application with audible feedback enabled and testing navigation within your application using directional controls.
You can simulate the experience for many users by enabling an accessibility service that speaks as you move around the screen. The Explore by Touch accessibility service, which is available on devices with Android 4.0 and later. The TalkBack accessibility service, by the Eyes-Free Project comes preinstalled on many Android devices.
To enable TalkBack on revisions of Android prior to Android 4.0:
Note: If the TalkBack accessibility service is not available, you can install it for free from Google Play.
To enable Explore by Touch on Android 4.0 and later:
Note: You must turn on TalkBack first, otherwise this option is not available.
As part of your accessibility testing, you can test navigation of your application using focus, even if your test devices does not have a directional controller. The Android Emulator provides a simulated directional controller that you can easily use to test navigation. You can also use a software-based directional controller, such as the one provided by the Eyes-Free Keyboard to simulate use of a D-pad.