if(Key.isDown) to be used in a button

I did it! Thanks! .. I can now move my character with the MouseEvent.MOUSE_DOWN for moving my character on the 'moving' animation and the MouseEvent.MOUSE_UP for moving my character on the 'still' animation..

But i still have one problem .. I cannot make my character jump, my codes on the KeyboardEvent works but if i tried to make it work with the MouseEvent it does not move.. Please Help! I don't know what to do with the   if (Key.isDown(Key.UP) && canjump)  codes

import flash.events.Event;

hero.gotoAndStop('still');

var Key:KeyObject = new KeyObject(stage);

var dy:Number=0;

var gravity:Number=1;

var canjump:Boolean = false;

jump_btn.addEventListener(MouseEvent.CLICK, onenter);

function onenter(Event:MouseEvent):void{

          dy+=gravity;

          if (hero.y>300){

                    dy=0;

                    canjump=true;

          }

          if (Key.isDown(Key.UP) && canjump){

                    dy=-20;

                    canjump = false;

          }

          hero.y+=dy;

}

right_btn.addEventListener(MouseEvent.MOUSE_DOWN,mouseDown);

function mouseDown(e:Event):void{

                    hero.x+=5;

                    hero.scaleX=-1;

                    hero.gotoAndStop('walking');

                    stage.addEventListener(MouseEvent.MOUSE_UP,mouseUp);

          }

function mouseUp(e:Event):void{

                    hero.gotoAndStop('still');

                    stage.removeEventListener(MouseEvent.MOUSE_UP,mouseUp);

          }