AS3:使用eventlistener向阶段添加多个按钮?

function init ():void
{
    var btn:Sprite;
    for ( var i:uint = 0; i < 100; i++ )
    {
        btn = new Sprite();
        btn.graphics.beginFill( Math.round( Math.random() * 0xFFFFFF ) );
        btn.graphics.drawRect( 0, 0, 50, 50 );
        btn.x = ( i % 20 ) * 50;
        btn.y = Math.floor( i / 20 ) * 50;

        // event listeners
        btn.addEventListener( MouseEvent.CLICK, btnClick );

        this.addChild( btn );
    }
}

function btnClick ( event:MouseEvent ):void
{
    var btn:Sprite = event.currentTarget as Sprite;
    btn.graphics.clear();
    btn.graphics.beginFill( Math.round( Math.random() * 0xFFFFFF ) );
    btn.graphics.drawRect( 0, 0, 50, 50 );
}