这次对布局进行优化，主要包含了首页tabview pageview 以及添加几个按钮的操作过程.主要使用到stack层叠布局，tabpview和pageview，tabview两个页面，一个关注，一个推荐，左右切换，pageview被包含在tabview里面.
抖音的顶部appbar 是悬浮层叠展示，而flutter的层叠组件是stack, 因此最外面采用stack, 其次中间是tabview，分别是关注和推荐两个选项卡，关注在没有登录的时候会弹出一个提示需要认证登录的页面，这里加了两个页面，subscriptionScreen.dart，另外一个是loginScreen.dart
@override Widget build(BuildContext context) { return Scaffold( //backgroundColor: Colors.transparent, body: Stack( //fit: StackFit.expand, children: <Widget>[ TabBarView( controller: _tabController, children: <Widget>[ Subscription(), PageView( allowImplicitScrolling: true, controller: _pageController, children: <Widget>[ Trending(), ], onPageChanged: (int index) { setState(() { currentIndex = index; }); }, ), ], ), Column( children: [ AppBar( backgroundColor: Colors.transparent, elevation: 0, centerTitle: true, leading: IconButton( icon: Icon(Icons.tv), onPressed: () { print('点击了直播按钮'); }), actions: <Widget>[ //导航栏右侧菜单 IconButton( icon: Icon(Icons.search), onPressed: () { print('点击了搜索按钮'); }), ], title: TabBar( indicator: UnderlineTabIndicator( borderSide: BorderSide(width: 2.0, color: Colors.white), insets: EdgeInsets.symmetric(horizontal: 18.0)), labelStyle: TextStyle(fontSize: 18), isScrollable: true, controller: _tabController, tabs: toptabs, onTap: (index) { print(index); }, ), ) ], ), ], ), bottomNavigationBar: bottomItems(), ); }