public static class View.AccessibilityDelegate extends Object
This class represents a delegate that can be registered in a View
to enhance accessibility support via composition rather via inheritance.
It is specifically targeted to widget developers that extend basic View
classes i.e. classes in package android.view, that would like their
applications to be backwards compatible.
For more information about making applications accessible, read the Accessibility developer guide.
A scenario in which a developer would like to use an accessibility delegate
is overriding a method introduced in a later API version then the minimal API
version supported by the application. For example, the method
View.onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo) is not available
in API version 4 when the accessibility APIs were first introduced. If a
developer would like his application to run on API version 4 devices (assuming
all other APIs used by the application are version 4 or lower) and take advantage
of this method, instead of overriding the method which would break the application's
backwards compatibility, he can override the corresponding method in this
delegate and register the delegate in the target View if the API version of
the system is high enough i.e. the API version is same or higher to the API
version that introduced
View.onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo).
Here is an example implementation:
if (Build.VERSION.SDK_INT >= 14) {
// If the API version is equal of higher than the version in
// which onInitializeAccessibilityNodeInfo was introduced we
// register a delegate with a customized implementation.
View view = findViewById(R.id.view_id);
view.setAccessibilityDelegate(new AccessibilityDelegate() {
public void onInitializeAccessibilityNodeInfo(View host,
AccessibilityNodeInfo info) {
// Let the default implementation populate the info.
super.onInitializeAccessibilityNodeInfo(host, info);
// Set some other information.
info.setEnabled(host.isEnabled());
}
});
}
This delegate contains methods that correspond to the accessibility methods in View. If a delegate has been specified the implementation in View hands off handling to the corresponding method in this delegate. The default implementation the delegate methods behaves exactly as the corresponding method in View for the case of no accessibility delegate been set. Hence, to customize the behavior of a View method, clients can override only the corresponding delegate method without altering the behavior of the rest accessibility related methods of the host view.
| Constructor and Description |
|---|
View.AccessibilityDelegate() |
| Modifier and Type | Method and Description |
|---|---|
boolean |
dispatchPopulateAccessibilityEvent(View host,
AccessibilityEvent event)
Dispatches an
AccessibilityEvent to the host View first and then
to its children for adding their text content to the event. |
AccessibilityNodeProvider |
getAccessibilityNodeProvider(View host)
Gets the provider for managing a virtual view hierarchy rooted at this View
and reported to
AccessibilityServices
that explore the window content. |
void |
onInitializeAccessibilityEvent(View host,
AccessibilityEvent event)
Initializes an
AccessibilityEvent with information about the
the host View which is the event source. |
void |
onInitializeAccessibilityNodeInfo(View host,
AccessibilityNodeInfo info)
Initializes an
AccessibilityNodeInfo with information about the host view. |
void |
onPopulateAccessibilityEvent(View host,
AccessibilityEvent event)
Gives a chance to the host View to populate the accessibility event with its
text content.
|
boolean |
onRequestSendAccessibilityEvent(ViewGroup host,
View child,
AccessibilityEvent event)
Called when a child of the host View has requested sending an
AccessibilityEvent and gives an opportunity to the parent (the host)
to augment the event. |
boolean |
performAccessibilityAction(View host,
int action,
Bundle args)
Performs the specified accessibility action on the view.
|
void |
sendAccessibilityEvent(View host,
int eventType)
Sends an accessibility event of the given type.
|
void |
sendAccessibilityEventUnchecked(View host,
AccessibilityEvent event)
Sends an accessibility event.
|
public void sendAccessibilityEvent(View host, int eventType)
The default implementation behaves as View#sendAccessibilityEvent(int) for the case of no accessibility delegate
been set.
host - The View hosting the delegate.eventType - The type of the event to send.View#sendAccessibilityEvent(int)public boolean performAccessibilityAction(View host, int action, Bundle args)
AccessibilityNodeInfo.
The default implementation behaves as
View#performAccessibilityAction(int, Bundle) for the case of
no accessibility delegate been set.
action - The action to perform.View#performAccessibilityAction(int, Bundle)public void sendAccessibilityEventUnchecked(View host, AccessibilityEvent event)
sendAccessibilityEvent(View, int) but takes as an argument an
empty AccessibilityEvent and does not perform a check whether
accessibility is enabled.
The default implementation behaves as
View#sendAccessibilityEventUnchecked(AccessibilityEvent) for
the case of no accessibility delegate been set.
host - The View hosting the delegate.event - The event to send.View#sendAccessibilityEventUnchecked(AccessibilityEvent)public boolean dispatchPopulateAccessibilityEvent(View host, AccessibilityEvent event)
AccessibilityEvent to the host View first and then
to its children for adding their text content to the event.
The default implementation behaves as
View#dispatchPopulateAccessibilityEvent(AccessibilityEvent) for
the case of no accessibility delegate been set.
host - The View hosting the delegate.event - The event.View#dispatchPopulateAccessibilityEvent(AccessibilityEvent)public void onPopulateAccessibilityEvent(View host, AccessibilityEvent event)
The default implementation behaves as
View#onPopulateAccessibilityEvent(AccessibilityEvent) for
the case of no accessibility delegate been set.
host - The View hosting the delegate.event - The accessibility event which to populate.View#onPopulateAccessibilityEvent(AccessibilityEvent)public void onInitializeAccessibilityEvent(View host, AccessibilityEvent event)
AccessibilityEvent with information about the
the host View which is the event source.
The default implementation behaves as
View#onInitializeAccessibilityEvent(AccessibilityEvent) for
the case of no accessibility delegate been set.
host - The View hosting the delegate.event - The event to initialize.View#onInitializeAccessibilityEvent(AccessibilityEvent)public void onInitializeAccessibilityNodeInfo(View host, AccessibilityNodeInfo info)
AccessibilityNodeInfo with information about the host view.
The default implementation behaves as
View#onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo) for
the case of no accessibility delegate been set.
host - The View hosting the delegate.info - The instance to initialize.View#onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo)public boolean onRequestSendAccessibilityEvent(ViewGroup host, View child, AccessibilityEvent event)
AccessibilityEvent and gives an opportunity to the parent (the host)
to augment the event.
The default implementation behaves as
ViewGroup#onRequestSendAccessibilityEvent(View, AccessibilityEvent) for
the case of no accessibility delegate been set.
host - The View hosting the delegate.child - The child which requests sending the event.event - The event to be sent.ViewGroup#onRequestSendAccessibilityEvent(View, AccessibilityEvent)public AccessibilityNodeProvider getAccessibilityNodeProvider(View host)
AccessibilityServices
that explore the window content.
The default implementation behaves as
View#getAccessibilityNodeProvider() for
the case of no accessibility delegate been set.
AccessibilityNodeProvider