たぶんこのようなもの
AppBar(bottom: PreferredSize(child: Container(color: Colors.orange, height: 4.0,), preferredSize: Size.fromHeight(4.0)),)
真にカスタマイズ可能なデザインが必要な場合は、理想的には独自のappbarを作成する必要があります。例:
class MyAppbar extends StatelessWidget implements PreferredSizeWidget {
final Widget title;
const MyAppbar({Key key, this.title}) : super(key: key);
@override
Widget build(BuildContext context) {
return Material(
elevation: 26.0,
color: Colors.white,
child: Container(
padding: const EdgeInsets.all(10.0),
alignment: Alignment.centerLeft,
decoration: BoxDecoration(
border: Border(
bottom: BorderSide(
color: Colors.deepOrange,
width: 3.0,
style: BorderStyle.solid,
),
),
),
child: title,
),
);
}
final Size preferredSize = const Size.fromHeight(kToolbarHeight);
}