Flutter change custom AppBar height - flutter

Question

I tried this link and it didn't work.
In this code when I try to change height of AppBar, but it doesn't any change.
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.transparent,
body: Container(
height: double.infinity,
child: Column(
children: <Widget>[
PreferredSize(
preferredSize: Size.fromHeight(150.0),
child: AppBar(
backgroundColor: Colors.white.withOpacity(0.9),
title: Container(height: 150.0,),
),
)
],
)),
);
}
Note: My AppBar(...) isn't used in appBar:

Answer 1

Just use toolbarHeight:
appBar: AppBar(
toolbarHeight: 150, // This is your height!
title: Text('AppBar'),
)
However, if you don't want to use appBar property
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.transparent,
body: Container(
height: double.infinity,
child: Column(
children: <Widget>[
Container(
height: 150, // height of AppBar
child: AppBar(
backgroundColor: Colors.blue.withOpacity(0.9),
title: Text("AppBar"),
),
)
],
),
),
);
}

Answer 2

class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new Scaffold(
body: Stack(
children: <Widget>[
Container(
color: Colors.blue,
),
new Positioned(
top: 0.0,
left: 0.0,
right: 0.0,
child: AppBar(
title: Text('App Bar'),
backgroundColor: Colors.green,
),
),
],
)),
);
}
}

Answer 3

For more controls , Use the PreferedSize widget to create your own appBar
Example :
appBar: PreferredSize(
preferredSize: Size(100, 80), //width and height
// The size the AppBar would prefer if there were no other constraints.
child: SafeArea(
child: Container(
height: 100,
color: Colors.red,
child: Center(child: Text('Fluter is great')),
),
),
),
Don't forget to use a SafeArea widget if you don't have a safeArea
Output :