Ans:

addEventListner in MXML component:

<?xml version="1.0" encoding = 'utf-8'?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">

  <mx:Script>
    import mx.controls.Alert;

    public function Handler():void{
      b1.addEventListener(MouseEvent.CLICK, alertbox, false, 0); 
    }

    public function Handler1():void{
      t1.text = 'click event disabled ';
      b2.addEventListener(MouseEvent.CLICK, alertbox, true, 0);
    }

    public function alertbox(event:Event):void{
      Alert.show('click event occured');
    }

  </mx:Script> 

    <mx:Button id = 'b1' label = 'b1 control' click = 'Handler()'/>

    <mx:HBox>
      <mx:Button id = 'b2' label = 'b2 control' click = 'Handler1()'/>
      <mx:TextInput id = 't1' editable = 'false'/>
    </mx:HBox>

  <mx:Script>

    public function message(event:Event):void{
      Alert.show('welcome to Flex World');
    } 

  </mx:Script>

  <mx:HBox>
    <mx:Label text = 'TextInput t2'/>
    <mx:TextInput id = 't2' 
      click = 't2.addEventListener(MouseEvent.CLICK, message, true, 0);'
      editable = 'true'/> 
  </mx:HBox>

  <mx:HBox>
    <mx:Label text = 'TextInput t3'/>
    <mx:TextInput id = 't3' 
      click = 't3.addEventListener(MouseEvent.CLICK, message, false, 0);'
       editable = 'false'/>
  </mx:HBox>

</mx:Application>

addEventListner in Action Script component:

package myComponents
{
    import mx.controls.TextArea;
    import flash.events.Event;

    public class ModalText extends TextArea {

        public function ModalText() {
            super();  

            addEventListener("enableChanged", enableChangedListener);
        }

        public function enableInput(value:Boolean):void {
            dispatchEvent(new Event("enableChanged"));
        }

        private function enableChangedListener(eventObj:Event):void {
            // Handle event.
        }
    }
}