how to set CupertinoSegmentedControl height?

Question

I am trying to use CupertinoSegmentedControl from the flutter Cupertino library in the AppBar using the bottom attribute to achieve the following design (height = 32)

so I tried the following :

@override
    Widget build(BuildContext context) {
        return Scaffold(
                appBar: AppBar(
                    elevation: 2,
                    backgroundColor: Colors.white,
                    centerTitle: true,
                    title: Text(this.widget.title, style: TextStyle(color: Colors.black)),
                    bottom: PreferredSize(
        child: Padding(
          padding: const  EdgeInsets.only(top: 8, bottom: 12),
          child: Row(
            children: <Widget>[
              SizedBox(width: 24),
              Expanded(
                child: CupertinoSegmentedControl(
                  children: this.widget.tabs,
                  groupValue: this._selectedTab,
                  onValueChanged: (value) {
                    this.setState(() => this._selectedTab = value);
                    this._tabController.animateTo(value);
                  }
                ),
              ),
              SizedBox(width: 24)
            ],
          ),
        ),
        preferredSize: Size(double.infinity, 48)
      )
                ),
                body: new TabBarView(
                    controller: this._tabController,
                    children: this.widget.views,
                ));
    } 

Answer 1

Here is full example based on @shadowsheep 's answer but improve version.

my_cupertino_segmented_control.dart

class MyCupertinoSegmentedControl extends StatelessWidget {
  final Map<int, Widget> children;
  final int? groupValue;
  final Function(int)? onValueChanged;

  const MyCupertinoSegmentedControl(
      {required this.children,
      this.groupValue,
      this.onValueChanged,
      super.key});

  @override
  Widget build(BuildContext context) {
    return PreferredSize(
        preferredSize: const Size(double.infinity, 48),
        child: Padding(
          padding: const EdgeInsets.only(top: 8, bottom: 12),
          child: Row(
            children: <Widget>[
              const SizedBox(width: 24),
              Expanded(
                child: CupertinoSegmentedControl<int>(
                    children: children,
                    groupValue: groupValue,
                    onValueChanged: (value) {
                      onValueChanged?.call(value);
                    }),
              ),
              const SizedBox(width: 24)
            ],
          ),
        ));
  }
}

It wrapped the annoying details to a simple widgets.

example.dart

import 'package:flutter/cupertino.dart';
import 'package:my_project/views/my_cupertino_segmented_control.dart';

class HomePageScaffold extends StatelessWidget {
  const HomePageScaffold({super.key});

  @override
  Widget build(BuildContext context) {
    return const CupertinoPageScaffold(
      navigationBar: CupertinoNavigationBar(
        middle: Text('Segmented Control Example'),
      ),
      child: HomePage(),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({super.key});

  @override
  State<StatefulWidget> createState() {
    return HomePageState();
  }
}

class HomePageState extends State<HomePage> {
  Map<int, Widget> segmentedWidgets = {};
  List<Widget> tabWidgets = [];
  int selectedIndex = 0;

  @override
  void initState() {
    super.initState();
    _loadSegmentedWidgets();
    _loadTabWidgets(); //Method to add the Children as user selected.
  }

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: Column(
        children: <Widget>[
          MyCupertinoSegmentedControl(
              children: segmentedWidgets,
              groupValue: selectedIndex,
              onValueChanged: (value) {
                setState(() {
                  selectedIndex = value;
                });
              }),
          tabWidgets[selectedIndex],
        ],
      ),
    );
  }

  void _loadSegmentedWidgets() {
    for (int i = 0; i < 4; i++) {
      segmentedWidgets[i] = Padding(
        padding: const EdgeInsets.all(8.0),
        child: Text("Tab ${i + 1}"),
      );
    }
  }

  void _loadTabWidgets() {
    for (int i = 0; i < 4; i++) {
      tabWidgets.add(
        Center(
          child: Text("Detail ${i + 1}"),
        ),
      );
    }
  }
}

It's initialize the CupertinoPageScaffold and 4 tabs with tab details.

Here's preview

Answer 2

just add Padding widget, or margin property to Container and wrap your Widgets in your "tabs" collection (in you case it is this.widget.tabs) with it

in my case

CupertinoSegmentedControl<int>(
            children: segmentTextWidgets,
            ...
          ),


final Map<int, Widget> segmentTextWidgets = <int, Widget>{
    0: Container(
      margin: const EdgeInsets.symmetric(vertical: 16),
      child: Text("Tab 1 title"),
    ),
    1: Container(
      margin: const EdgeInsets.symmetric(vertical: 16),
      child: Text("Tab 2 title"),
    ),
  };

Answer 3

Is something like that similar to the layout that you want? (Removing the green color of course ^_^)

Play around with the Container and PreferredSize heights to adjust the height to fit your needs.

Scaffold(
    appBar: AppBar(
        elevation: 2,
        backgroundColor: Colors.white,
        centerTitle: true,
        title:
            Text(this.widget.title, style: TextStyle(color: Colors.black)),
        bottom: PreferredSize(
            child: Row(
              children: [
                Expanded(
                  child: Container(
                    height: 48,
                    color: Colors.lightGreenAccent,
                    child: CupertinoSegmentedControl(
                        children: children,
                        groupValue: this._selectedTab,
                        onValueChanged: (value) {
                          this.setState(() => this._selectedTab = value);
                        }),
                  ),
                )
              ],
            ),
            preferredSize: Size(double.infinity, 48))),
    body: Center(
        child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Text('hello')
        ]
        )
    )
);

UPDATE:

As kazimad pointed out, if you want to increase the segmented control height and not only add padding to it insiede the app bar, you can add a Padding widget to your tabs, like that:

@override
Widget build(BuildContext context) {
  return Scaffold(
      appBar: AppBar(
          elevation: 2,
          backgroundColor: Colors.white,
          centerTitle: true,
          title:
              Text(this.widget.title, style: TextStyle(color: Colors.black)),
          bottom: PreferredSize(
              child: Padding(
                padding: const EdgeInsets.only(top: 8, bottom: 12),
                child: Row(
                  children: <Widget>[
                    SizedBox(width: 24),
                    Expanded(
                      child: CupertinoSegmentedControl(
                          children: const <int, Widget>{
                            0: Padding(
                                padding: EdgeInsets.all(8.0),
                                child: Text('Midnight')),
                            1: Padding(
                                padding: EdgeInsets.all(8.0),
                                child: Text('Viridian')),
                            2: Padding(
                                padding: EdgeInsets.all(8.0),
                                child: Text('Cerulean'))
                          },
                          groupValue: this._selectedTab,
                          onValueChanged: (value) {
                            // TODO: - fix it
                          }),
                    ),
                    SizedBox(width: 24)
                  ],
                ),
              ),
              preferredSize: Size(double.infinity, 48))),
      body: Center(
          child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [Text('hello')])));
}