如何在Flash上正确使用KeyboardEvent

在我开始的游戏中,我有一个KeyboardEvent问题。我有三个类,一个用于处理级别,一个是实际级别,另一个用于表示化身:

数量

import flash.display.MovieClip;
import flash.events.Event;

public class Fase extends Cena
{
    var avatar:Avatar;

    public function Fase()
    {
        // constructor code
        this.addEventListener(Event.ADDED_TO_STAGE, onAdded);
    }

    public function onAdded(e:Event)
    {
        avatar = new Avatar();
        this.addChild(avatar);
        avatar.x = stage.width/2;
        avatar.y = 30;

    }

    public function die()
    {
        this.removeEventListener(Event.ADDED_TO_STAGE, onAdded);
        (this.parent as ScreenHandler).removeChild(this);
    }

}

阿凡达

public class Avatar extends MovieClip
{

    public function Avatar()
    {
        // constructor code
        this.addEventListener(Event.ADDED_TO_STAGE, onAdded);
    }

    public function onAdded(e:Event)
    {
        //stage.focus=this;
        this.addEventListener(KeyboardEvent.KEY_DOWN, apertou);
    }

    public function apertou(event:KeyboardEvent)
    {
        trace("o");
        if(event.keyCode == Keyboard.LEFT)
        {
            this.x++;
        }
    }

}

我在这两个类上都有所有的包,如果我使用舞台,一切都可以。focus=这是在阿凡达上,但如果我在游戏执行过程中点击其他地方,焦点就会丢失,不再有效。有人能帮我吗?

提前谢谢