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 than 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 their 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, they 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 the same as or higher than 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.

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 AccessibilityDelegate.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

Public constructors

public AccessibilityDelegate ()

Public methods

public void addExtraDataToAccessibilityNodeInfo (View host, 
                AccessibilityNodeInfo info, 
                String extraDataKey, 
                Bundle arguments)

public boolean dispatchPopulateAccessibilityEvent (View host, 
                AccessibilityEvent event)

public AccessibilityNodeProvider getAccessibilityNodeProvider (View host)

public void onInitializeAccessibilityEvent (View host, 
                AccessibilityEvent event)

public void onInitializeAccessibilityNodeInfo (View host, 
                AccessibilityNodeInfo info)

public void onPopulateAccessibilityEvent (View host, 
                AccessibilityEvent event)

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

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

public void sendAccessibilityEvent (View host, 
                int eventType)

public void sendAccessibilityEventUnchecked (View host, 
                AccessibilityEvent event)