How to create a custom AppBar widget?

import 'package:flutter/material.dart';class CustomAppBar extends StatefulWidget implements PreferredSizeWidget {    CustomAppBar({Key key}) : preferredSize = Size.fromHeight(kToolbarHeight), super(key: key);    @override    final Size preferredSize; // default is 56.0    @override    _CustomAppBarState createState() => _CustomAppBarState();}class _CustomAppBarState extends State<CustomAppBar>{    @override    Widget build(BuildContext context) {        return AppBar( title: Text("Sample App Bar") );    }}

Hopefully this helps

class AppBars extends AppBar {  AppBars():super(    iconTheme: IconThemeData(      color: Colors.black, //change your color here    ),    backgroundColor: Colors.white,    title: Text(      "this is app bar",      style: TextStyle(color: Color(Constant.colorBlack)),    ),    elevation: 0.0,    automaticallyImplyLeading: false,    actions: <Widget>[      IconButton(        icon: Icon(Icons.notifications),        onPressed: () => null,      ),      IconButton(        icon: Icon(Icons.person),        onPressed: () => null,      ),    ],  );}

Widget build(BuildContext context) {  return new Scaffold(    appBar: setAppBar(),    body: new Container() // add rest of the UI  );}Widget setAppBar() {  return new AppBar(  //backgroundColor: Colors.blue,  //automaticallyImplyLeading: true  elevation: 0.0, // for elevation  titleSpacing: 0.0, // if you want remove title spacing with back button  title:  UtilCommonWidget.addTextMedium('About US', Colors.white, 20.0, 1),  actions: <Widget>[    addAppBarActionWidgetProfile(icon, 30.0, 30.0, 15.0) // add your custom action widget  ],//Action icon search as search icon, notification icon  leading: new Material( //Custom leading icon, such as back icon or other icon    color: Colors.transparent,    child: new InkWell(      onTap: () {        Navigator.of(context).pop();      },      splashColor: UniQueryColors.colorGradientEnd.withOpacity(.5),      child: new Container(          padding: const EdgeInsets.fromLTRB(12.0, 16.0, 16.0, 16.0),          child: UtilCommonWidget.addImage(Constant.iconBack, 19.0, 10.0))      ),  ) );}