Flutter set max width for AppBar - flutter

Question

I want to set the max width of an AppBar like this:
PreferredSize(
preferredSize: Size(500, 200),
child: AppBar(
flexibleSpace: _AppHeader(),
),
)
But this only sets the height. How is is possible to set the width?

Answer 1

Looks like this is an open issue (https://github.com/flutter/flutter/issues/54784).
As suggested there by #imeDevelopers you can use Stack to "hack" an AppBar with max width:
If you use Stack, you also get to decide if the AppBar will scroll with the content or not.
Use this code to keep the AppBar in place even when scrolling (default AppBar behaviour):
const double appBarWidth = 980;
Scaffold(
body: Stack(
children: [
ListView(
shrinkWrap: true,
children: [
Padding(
padding: const EdgeInsets.only(top: 56),
child: Column(
children: [
...[Colors.green, Colors.indigo, Colors.amber].map(
(c) => Container(
color: Colors.red,
child: Center(
child: Container(
height: 1000,
width: appBarWidth,
color: c,
),
),
),
)
],
),
),
],
),
Container(
width: double.infinity,
height: 56,
color: Colors.lime,
),
Positioned(
left: (MediaQuery.of(context).size.width - appBarWidth) / 2,
child: Container(
width: appBarWidth,
child: AppBar(
elevation: 0,
title: const Text('TITLE'),
actions: [
...[1, 2, 3].map(
(i) => TextButton(
style: TextButton.styleFrom(
primary: Theme.of(context).colorScheme.onPrimary),
onPressed: () {},
child: Text('ACTION $i'),
),
),
],
),
),
)
],
),
);
Use this code if you want the AppBar to scroll with the content:
const double appBarWidth = 980;
Scaffold(
body: ListView(
shrinkWrap: true,
children: [
Stack(
children: [
Container(
width: double.infinity,
height: 56,
color: Colors.lime,
),
Positioned(
left: (MediaQuery.of(context).size.width - appBarWidth) / 2,
child: Container(
width: appBarWidth,
child: AppBar(
elevation: 0,
title: const Text('TITLE'),
actions: [
...[1, 2, 3].map(
(i) => TextButton(
style: TextButton.styleFrom(
primary: Theme.of(context).colorScheme.onPrimary),
onPressed: () {},
child: Text('ACTION $i'),
),
),
],
),
),
)
],
),
Column(
children: [
...[Colors.green, Colors.indigo, Colors.amber].map(
(c) => Container(
color: Colors.red,
child: Center(
child: Container(
height: 1000,
width: appBarWidth,
color: c,
),
),
),
)
],
),
],
),
);