//d打开菜单
    public void openMenu()
    {
        if(isOpen) return;
        this.smoothScrollTo(0,0);
        isOpen=true;
    }
    //关闭菜单
    public void closeMenu()
    {
        if(!isOpen)return;
        this.smoothScrollTo(mMenuWidth,0);
        isOpen=false;
    }
//切换菜单

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {

        if(keyCode==KeyEvent.KEYCODE_BACK)
        {
           closeMenu();
        }
        return super.onKeyDown(keyCode, event);
       /* return isOpen=false;*/
    }

    public void toggle(){


        if(isOpen)
        {
            closeMenu();
        }else
        {
            openMenu();
        }
    }

请问如何监听手机返回按键，，将菜单栏关闭，而不是直接退出程序。