View.AccessibilityDelegate

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.

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 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 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.

Note: On platform versions prior to API 23, delegate methods on views in the android.widget.* package are called before host methods. This prevents certain properties such as class name from being modified by overriding onInitializeAccessibilityNodeInfo(View, AccessibilityNodeInfo), as any changes will be overwritten by the host class.

Starting in API 23, delegate methods are called after host methods, which all properties to be modified without being overwritten by the host class.

Summary

Inherited methods

From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait(long millis, int nanos) Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed. final void wait(long millis) Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed. final void wait() Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object.

Public constructors

View.AccessibilityDelegate ()

Public methods

boolean dispatchPopulateAccessibilityEvent (View host, 
                AccessibilityEvent event)

AccessibilityNodeProvider getAccessibilityNodeProvider (View host)

void onInitializeAccessibilityEvent (View host, 
                AccessibilityEvent event)

void onInitializeAccessibilityNodeInfo (View host, 
                AccessibilityNodeInfo info)

void onPopulateAccessibilityEvent (View host, 
                AccessibilityEvent event)

boolean onRequestSendAccessibilityEvent (ViewGroup host, 
                View child, 
                AccessibilityEvent event)

boolean performAccessibilityAction (View host, 
                int action, 
                Bundle args)

void sendAccessibilityEvent (View host, 
                int eventType)

void sendAccessibilityEventUnchecked (View host, 
                AccessibilityEvent event)