flutter 隐藏导航栏appBar

当有的BottomNavigationBar对应的初始页面不需要导航栏APPBar，但是需要用到appBar进行页面跳转时，可以先隐藏APPBar，在AppBar外包裹一层Offstage，具体代码如下：

//初始值
var _currentIndex = 0;
var appTitle = ['首页','病例','商城','我的'];

@override
Widget build(BuildContext context) {
return Scaffold(
appBar: PreferredSize(
child: Offstage(
offstage: _currentIndex == 3?true:false,
child: AppBar(
centerTitle:true ,
title: Text(appTitle[_currentIndex]),

              //  toolbarOpacity:_currentIndex==3?0:1 ,
              backgroundColor: _currentIndex!= 3? 
              Theme.of(context).accentColor:Colors.transparent,
        ),
    ),
     preferredSize:Size.fromHeight(MediaQuery.of(context).size.height * 0.07),
    ),
   body: getCurrentPage(),
   bottomNavigationBar: BottomNavigationBar(
    type: BottomNavigationBarType.fixed,
     items: [
        BottomNavigationBarItem(icon: Icon(Icons.home), title: Text(appTitle[0])),
        BottomNavigationBarItem(icon: Icon(Icons.business), title: Text(appTitle[1])),
        BottomNavigationBarItem(icon: Icon(Icons.local_mall), title: Text(appTitle[2])),
        BottomNavigationBarItem(icon: Icon(Icons.person), title: Text(appTitle[3])),
   ],
   currentIndex:_currentIndex,
   fixedColor: Colors.deepPurple,
   onTap: _clickBottermIterm,
   ),
);

}