How can I place a container laid out above a Scaffold? - flutter

Question

I would like to have a persistent container occupy the space about my material Scaffolds AppBar. I would like the Scaffold to resize to take up the available space.
When I try to do this, my Scaffold continues to be the height of the entire screen, and it is simply pushed lower, with a portion overflowing off the screen.
Is there a way I can have the Scaffold to resize to the available space?
Here is what I have coded so far...
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: const MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
const MyHomePage({Key? key}) : super(key: key);
#override
State<MyHomePage> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
#override
Widget build(BuildContext context) {
return PersistenTopBar(
child: Scaffold(
appBar: AppBar(
title: const Text("Test App"),
),
body: Container(),
),
);
}
}
class PersistenTopBar extends StatelessWidget {
final Widget child;
const PersistenTopBar({Key? key , required this.child }) : super(key: key);
#override
Widget build(BuildContext context) {
var mediaQuery = MediaQuery.of(context);
return Column(
children: [
Container(
width: double.infinity,
height: 200,
color: Colors.red,
),
SizedBox(
width: mediaQuery.size.width,
height: mediaQuery.size.height,
child: child,
),
],
);
}
}

Answer 1

You could also create a CustomAppBar that would take as children a topChild and an appBar.
class CustomAppBar extends StatelessWidget implements PreferredSizeWidget {
final double height;
final Widget topChild;
final AppBar appBar;
const CustomAppBar(
{Key? key,
this.height = 200.0,
required this.topChild,
required this.appBar})
: super(key: key);
#override
Widget build(BuildContext context) {
return Column(
children: [
Expanded(child: topChild),
appBar,
],
);
}
#override
Size get preferredSize => Size.fromHeight(height);
}
Full code sample
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData.light(),
home: const MyHomePage(),
);
}
}
class MyHomePage extends StatelessWidget {
const MyHomePage({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: CustomAppBar(
topChild: Container(color: Colors.red),
appBar: AppBar(title: const Text('My awesome Test App')),
),
body: const Center(
child: Text(
"Test App",
style: TextStyle(fontSize: 32.0),
),
),
);
}
}
class CustomAppBar extends StatelessWidget implements PreferredSizeWidget {
final double height;
final Widget topChild;
final AppBar appBar;
const CustomAppBar(
{Key? key,
this.height = 200.0,
required this.topChild,
required this.appBar})
: super(key: key);
#override
Widget build(BuildContext context) {
return Column(
children: [
Expanded(child: topChild),
appBar,
],
);
}
#override
Size get preferredSize => Size.fromHeight(height);
}

Answer 2

the available space = mediaQuery.size.height - the Height of the Container above the appBar so the SizedBox under the appBar wil be :
SizedBox(
width: mediaQuery.size.width,
height: mediaQuery.size.height - 200,
child: child,
),
the result:
or you can wrap your SizedBox with Expanded Widget :
Expanded(
child: SizedBox(
width: mediaQuery.size.width,
child: child,
),
),
the same result :