Key handler does not see global objects

programming flash
1

I’m making mobile aplication in Flash Lite 3.0. I’ve wanted to add key event handling, when some problem occured. Below is my class, which controls main menu with three buttons. Function onKey() is an event handler, but unfortunently it does not detect any global objects (e.g. currentButton or Butons). Only trace() and local code are working. How can I deal with it?

class MainMenuInit
{
    var i:Number;
    
    var Buttons:Array;
    var currentButton:Number;
    var keyListener:Object;
    
    var objectLocator:ObjectLocator;
    
    function MainMenuInit(objectLocator:ObjectLocator)
    {
        this.objectLocator = objectLocator;
        Buttons = [];
        init();
        handlers();
    }
    
    function init():Void
    {
        var mainMenu = _root.attachMovie('MainMenu', 'mainMenu', 1,{_x:0, _y:0});
        
        currentButton = 0;
        
        if( Buttons.length == 0)
            for(i = 1; i<4; i++)
                Buttons.push(mainMenu["Button"+i]);
                                                 
        Buttons[0].gotoAndStop(2);
        Buttons[1].gotoAndStop(3);
        Buttons[2].gotoAndStop(1);
        
    }
    
    function handlers():Void
    {
        keyListener = new Object();
        keyListener.onKeyDown = onKey;
        Key.addListener( keyListener );
    }
    
    function onKey():Void
    {
        if( currentButton < Buttons.length - 1 )
        {
            Buttons[currentButton].gotoAndStop(1);
            currentButton++;
            if(Buttons[currentButton].currentFrame == 3) 
                currentButton++;
            Buttons[currentButton].gotoAndStop(2);
        }
        trace(currentButton);
    }

}