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,
        ),
      ],
    );
  }
}

CodePudding user response：

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);
}

CodePudding user response：

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 :