Flutter中有很多Button组件，例如RaisedButton、FlatButton、IconButtton、OutlineButton、ButtonBar、FloatingActionButton等。
RaisedButton：凸起的按钮，其实就是Material Design风格的Button.
FlatButton:扁平化的按钮
OutlineButton:线框按钮
ButtonBar:按钮组
FloatingActionButton:浮动按钮

RaisedButton

FloatingActionButton

仿咸鱼首页居中的Button Demo

class Tabs extends StatefulWidget{
  final index;

  Tabs({this.index=0});

  @override
  State<StatefulWidget> createState() {
    return _TabsState(index);
  }

}

class _TabsState extends State<Tabs>{
  List<Widget> _page=[HomePage(),SettignPage(),MinePage()]; //用于存放对应的页面
  int _bottomIndex=0;

  _TabsState(index){
   _bottomIndex=index;
  }
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Scaffold(
      
      appBar: AppBar(title: Text('Flutter BottomNavigationBar'),),
      body:this._page[_bottomIndex],
      floatingActionButton: Container(
        width: 80,
        height: 80,
        padding: EdgeInsets.all(10),
        margin: EdgeInsets.only(top: 8),
        decoration: BoxDecoration(
          borderRadius: BorderRadius.circular(40),
        ),
        child:  FloatingActionButton(
          child: Icon(Icons.add),
          onPressed: (){
              setState(() {
                _bottomIndex=1;
              });
          },
        ),
      ),
      floatingActionButtonLocation:FloatingActionButtonLocation.centerDocked,
      bottomNavigationBar: BottomNavigationBar(
        iconSize: 25,

        type: BottomNavigationBarType.fixed,  //配置底部tabs可以有多个按钮
        currentIndex: this._bottomIndex,//对应点击/显示哪个底部导航栏按钮
        onTap: (index){ //bottomNavigationBar的点击事件
          setState(() {
            this._bottomIndex=index;  //将选中的下标进行替换
          });
        },
        items: [
          BottomNavigationBarItem(
              icon: Icon(Icons.home),
              title: Text('首页')
          ),
          BottomNavigationBarItem(
              icon: Icon(Icons.settings),
              title: Text('设置')
          ),
          BottomNavigationBarItem(
              icon: Icon(Icons.mood),
              title: Text('我的')
          ),
         
        ],
      ),
      drawer: Drawer(
        child: Column(
          children: <Widget>[
              Row(
                children: <Widget>[
                  UserAccountsDrawerHeader(

                  ),
                ],
              ),
            ListTile(
              leading: CircleAvatar(
                child: Icon(Icons.home),
              ),
              title: Text('空间'),
            ),
            Divider(),//一条线
            ListTile(
              leading: CircleAvatar(
                child: Icon(Icons.people),
              ),
              title: Text('用户中心'),
            ),
            Divider(),//一条线
          ],
        ),
      ),
      endDrawer: Drawer(
        child: Column(
          children: <Widget>[

            ListTile(
              leading: CircleAvatar(
                child: Icon(Icons.settings),
              ),
              title: Text('设置中心'),
            ),
            Divider(),//一条线
          ],
        )
      ),
    );
  }
}