CODE EXAMPLE FOR SWIFT

flutter custom appbar

class Sample1 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: Scaffold(
        drawer: Drawer(),
        appBar: MyCustomAppBar(
          height: 150,
        ),
        body: Center(
          child: FlutterLogo(
            size: MediaQuery.of(context).size.width / 2,
          ),
        ),
      ),
    );
  }
}

class MyCustomAppBar extends StatelessWidget implements PreferredSizeWidget {
  final double height;

  const MyCustomAppBar({
    Key key,
    @required this.height,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Container(
          color: Colors.grey[300],
          child: Padding(
            padding: EdgeInsets.all(30),
            child: AppBar(
                    title: Container(
                      color: Colors.white,
                      child: TextField(
                        decoration: InputDecoration(
                          hintText: "Search",
                          contentPadding: EdgeInsets.all(10),
                        ),
                      ),
                    ),
                    actions: [
                      IconButton(
                        icon: Icon(Icons.verified_user),
                        onPressed: () => null,
                      ),
                    ],
                  ) ,
          ),
        ),
      ],
    );
  }
  
 @override
  Size get preferredSize => Size.fromHeight(height);
}