Listen for events

The native implementation can dispatch events that the ActionScript extension code can listen for. This mechanism allows the native implementation to perform tasks asynchronously, notifying the ActionScript side when the task is complete.

The event target is the ExtensionContext instance. Therefore, use the addEventListener() method of the ExtensionContext instance to subscribe to events from the native implementation.

The following example adds code to TVChannelController to receive an event from the native implementation. The application using the extension calls the ActionScript extension class method scanChannels() , which in turn calls the native function "scanDeviceChannels" .

This native function asynchronously scans for all available channels. When it has completed the scan, it dispatches an event. The onStatus() method handles the event by querying the native method "getDeviceChannels" for the list of channels. The onStatus() method stores the list in the scannedChannelList data member, and dispatches an event to the application’s listening object. When the application object receives the event, it can call the ActionScript extension class property accessor availableChannels .

package  com.example { 
     public  class TVChannelController extends EventDispatcher {  
 
        private var extContext:ExtensionContext;  
        private var channel:int;  
        private var scannedChannelList:Vector.<int>; 
 
        public function TVChannelController() { 
            extContext = ExtensionContext.createExtensionContext( 
                            "com.example.TVControllerExtension", "channel"); 
            extContext.addEventListener(StatusEvent.STATUS, onStatus); 
        } 
        . 
        . 
        . 
        public function scanChannels():void { 
            extContext.call("scanDeviceChannels"); 
        } 
        public function get availableChannels():Vector.<int> { 
            return scannedChannelList; 
        } 
        private function onStatus(event:StatusEvent):void { 
            if ((event.level == "status") && (event.code == "scanCompleted")) { 
                scannedChannelList = (Vector.<int>)(extContext.call("getDeviceChannels")); 
                dispatchEvent (new Event ("scanCompleted") ); 
            }     
        } 
    } 
}

The example illustrates the following points:

The native implementation can dispatch only a StatusEvent object. Therefore, the addEventListener() method listens for the event type StatusEvent.STATUS .
The native implementation sets the code and level properties of the StatusEvent object. You can define the strings you want to use for these properties. In this example, the native implementation sets the level property to “ status" and the code property to "scanCompleted" . Typically, the level property of a StatusEvent has the value "status" , "info" , or "error" .
Because TVChannelController is a subclass of EventDispatcher, it can also dispatch an event. In this example, it dispatches an Event object with the type property "scanCompleted" . Any ActionScript object interested in this event can listen for it. For example, the following code shows a snippet from an AIR application that uses this extension. The application creates a TVChannelController object. Then, it asks the TVChannelController object to scan for channels. Then it waits for the scan to complete.
```
var channelController:TVChannelController = new TVChannelController(); 
channelController.addEventListener("scanCompleted", onChannelsScanned); 
channelController.scanChannels(); 
var channelList:Vector.<int>; 
 
private function onChannelsScanned(evt:Event):void { 
    if (evt.type == "scanCompleted") { 
        channelList = channelController.availableChannels;    } 
}
```