View.AccessibilityDelegate

Class Overview

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.

Summary

[Expand] Inherited Methods

From class java.lang.Object Object clone() Creates and returns a copy of this Object. boolean equals(Object o) Compares this instance with the specified object and indicates if they are equal. void finalize() Invoked when the garbage collector has detected that this instance is no longer reachable. final Class<?> getClass() Returns the unique instance of Class that represents this object's class. int hashCode() Returns an integer hash code for this object. final void notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. final void notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. String toString() Returns a string containing a concise, human-readable description of this object. final void wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object. final void wait(long millis, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires. final void wait(long millis) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.