import 'package:ajbaby/res/colors.dart';
import 'package:flutter/material.dart';


// ignore: must_be_immutable
class CustomTabBar extends StatefulWidget implements PreferredSizeWidget {
  Color containerBgColor;
  Color labelColor;
  Color unselectedLabelColor;
  Color indicatorColor;
  TabController tabController;
  List<Widget> tabsList = new List<Widget>();
  List<Widget> tabBarViewsList = new List<Widget>();

  // @required声明必传参数
  CustomTabBar({
    Key key,
    @required this.tabsList,
    @required this.tabBarViewsList,
    @required this.tabController,
    this.containerBgColor = YColors.color_FFFFFF,
    this.labelColor = YColors.color_FF5F6D,
    this.unselectedLabelColor = YColors.color_858585,
    this.indicatorColor = YColors.color_FF5F6D,
  }) : super(key: key);


  @override
  _CustomTabBarState createState() {
    return _CustomTabBarState();
  }


  @override
  // TODO: implement preferredSize
  Size get preferredSize => null;
}


class _CustomTabBarState extends State<CustomTabBar> with AutomaticKeepAliveClientMixin {
  @override
  void initState() {
    super.initState();
  }


  @override
  void dispose() {
    super.dispose();
//    widget.tabController.dispose();
  }


  @override
  Widget build(BuildContext context) {
    super.build(context);
    return Scaffold(
      appBar: PreferredSize(
          child: Container(
            color: widget.containerBgColor,
            child: TabBar(
              isScrollable: true,
              controller: widget.tabController,
              tabs: widget.tabsList,
              labelColor: widget.labelColor,
              unselectedLabelColor: widget.unselectedLabelColor,
              indicatorColor: widget.indicatorColor,
            ),
          ),
          preferredSize: Size.fromHeight(kToolbarHeight)),
      body: TabBarView(
        controller: widget.tabController,
        children: widget.tabBarViewsList,
      ),
    );
  }


  @override
  // TODO: implement wantKeepAlive
  bool get wantKeepAlive => true;
}

body: CustomTabBar(
  tabsList: _tabsList,
  tabBarViewsList: _tabBarViewsList,
  tabController: _tabController,
),

Navigator.of(context)
  .push(new MaterialPageRoute(builder: (context) {
    return new DetailPage();
  }));
 Navigator.pop(context);

class AppBar extends StatefulWidget implements PreferredSizeWidget

import 'package:flutter/material.dart';
import 'package:flutter_screenutil/flutter_screenutil.dart';

/// 这是一个可以指定SafeArea区域背景色的AppBar
/// PreferredSizeWidget提供指定高度的方法
/// 如果没有约束其高度，则会使用PreferredSizeWidget指定的高度

// ignore: must_be_immutable
class CustomAppbar extends StatefulWidget implements PreferredSizeWidget {
  final double contentHeight; //从外部指定高度
  Color navigationBarBackgroundColor; //设置导航栏背景的颜色
  Widget leadingWidget;
  Widget trailingWidget;
  String title;

  CustomAppbar({
    @required this.leadingWidget,
    @required this.title,
    this.contentHeight = 44,
    this.navigationBarBackgroundColor = Colors.white,
    this.trailingWidget,
  }) : super();

  @override
  State<StatefulWidget> createState() {
    return new _CustomAppbarState();
  }

  @override
  Size get preferredSize => new Size.fromHeight(contentHeight);
}

/// 这里没有直接用SafeArea，而是用Container包装了一层
/// 因为直接用SafeArea，会把顶部的statusBar区域留出空白
/// 外层Container会填充SafeArea，指定外层Container背景色也会覆盖原来SafeArea的颜色
///     var statusheight = MediaQuery.of(context).padding.top;  获取状态栏高度

class _CustomAppbarState extends State<CustomAppbar> {
  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return new Container(
      color: widget.navigationBarBackgroundColor,
      child: new SafeArea(
        top: true,
        child: new Container(
            decoration: new UnderlineTabIndicator(
              borderSide: BorderSide(width: 1.0, color: Color(0xFFeeeeee)),
            ),
            height: widget.contentHeight,
            child: new Stack(
              alignment: Alignment.center,
              children: <Widget>[
                Positioned(
                  left: 0,
                  child: new Container(
                    padding: const EdgeInsets.only(left: 5),
                    child: widget.leadingWidget,
                  ),
                ),
                new Container(
                  child: new Text(
                    widget.title,
                    style: new TextStyle(
                        fontSize: ScreenUtil().setSp(33, allowFontScalingSelf: true),
                        color: Color(0xFF333333),
                        fontWeight: FontWeight.w600),
                  ),
                ),
                Positioned(
                  right: 0,
                  child: new Container(
                    padding: const EdgeInsets.only(right: 5),
                    child: widget.trailingWidget,
                  ),
                ),
              ],
            )),
      ),
    );
  }
}

appBar: new CustomAppbar(
          title: '日历',
          leadingWidget: leftBarButtonItemWidget(),
          trailingWidget: rightBarButtonItemsWidget(),
        )

@override
 bool get wantKeepAlive => true;

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) => MaterialApp(
        title: "demo",
        home: MainPage(),
      );
}

class MainPage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => MainPageState();
}

class MainPageState extends State<MainPage> {
  int _currentIndex;
  List<Widget> _pages;

  @override
  void initState() {
    super.initState();
    _currentIndex = 0;
    _pages = List()..add(FirstPage("第一页"))..add(SecondPage("第二页"))..add(ThirdPage("第三页"));
  }

  @override
  Widget build(BuildContext context) => Scaffold(
        body: _pages[_currentIndex],
        bottomNavigationBar: BottomNavigationBar(
          items: getItems(),
          currentIndex: _currentIndex,
          onTap: onTap,
        ),
      );

  List<BottomNavigationBarItem> getItems() {
    return [
      BottomNavigationBarItem(icon: Icon(Icons.home), title: Text("Home")),
      BottomNavigationBarItem(icon: Icon(Icons.adb), title: Text("Adb")),
      BottomNavigationBarItem(icon: Icon(Icons.person), title: Text("Person"))
    ];
  }

  void onTap(int index) {
    setState(() {
      _currentIndex = index;
    });
  }
}

// with 混入
class DevicePageLayout extends  WidgetState<DevicePage>  with AutomaticKeepAliveClientMixin

@override
// TODO: implement wantKeepAlive
bool get wantKeepAlive => true;