问Flash:AS3-- setChildIndex问题

EN

stop();

//campaign
campaign_btn.addEventListener(MouseEvent.ROLL_OVER, roll1);
function roll1(event:MouseEvent):void {
    setChildIndex(campaign_btn, numChildren-1);
};

//survey
survey_btn.addEventListener(MouseEvent.ROLL_OVER, roll2);
function roll2(event:MouseEvent):void {
    setChildIndex(survey_btn, numChildren-1);
};

//project
project_btn.addEventListener(MouseEvent.ROLL_OVER, roll3);
function roll3(event:MouseEvent):void {
    setChildIndex(project_btn, numChildren-1);
};

//filestore
filestore_btn.addEventListener(MouseEvent.ROLL_OVER, roll4);
function roll4(event:MouseEvent):void {
    setChildIndex(filestore_btn, numChildren-1);
};

//website
website_btn.addEventListener(MouseEvent.ROLL_OVER, roll5);
function roll5(event:MouseEvent):void {
    setChildIndex(website_btn, numChildren-1);
};

//forms
forms_btn.addEventListener(MouseEvent.ROLL_OVER, roll6);
function roll6(event:MouseEvent):void {
    setChildIndex(forms_btn, numChildren-1);
};

//invoice
invoice_btn.addEventListener(MouseEvent.ROLL_OVER, roll7);
function roll7(event:MouseEvent):void {
    setChildIndex(invoice_btn, numChildren-1);
};

//CRM
CRM_btn.addEventListener(MouseEvent.ROLL_OVER, roll8);
function roll8(event:MouseEvent):void {
    setChildIndex(CRM_btn, numChildren-1);
};

//--------------------------back button------------------------------
back_btn.addEventListener(MouseEvent.CLICK, buttonClick1);
function buttonClick1(event:MouseEvent):void
{
    if(contains(campaign_btn))
    {
        removeChild(campaign_btn);
    }
        gotoAndPlay(1124);
}