Wizard Buttons - by Simon Lightfoot - Humpday Q&A :: 20th December 2023 #HumpdayQandA #Flutter #Dart - https://www.youtube.com/live/kJWtSAFnJxk?si=nWEXHtV1NmT6jJCd&t=6509

wizard_buttons.dart

// MIT License
//
// Copyright (c) 2023 Simon Lightfoot
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

void main() {
  runApp(MaterialApp(
    debugShowCheckedModeBanner: false,
    theme: ThemeData.light(),
    home: const Home(),
  ));
}

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

  @override
  State<Home> createState() => _HomeState();
}

class _HomeState extends State<Home> {
  @override
  Widget build(BuildContext context) {
    return Material(
      child: Center(
        child: Stack(
          children: [
            Positioned.fill(
              child: Placeholder(
                color: Colors.grey.shade300,
              ),
            ),
            Padding(
              padding: const EdgeInsets.symmetric(horizontal: 12.0),
              child: WizardButtons(
                previous: ElevatedButton(
                  onPressed: () {
                    //
                  },
                  child: const Text('Previous'),
                ),
                label: const Text('2/3'),
                next: ElevatedButton(
                  onPressed: () {
                    //
                  },
                  child: const Text(
                    'Next',
                    textAlign: TextAlign.center,
                  ),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

class WizardButtons extends MultiChildRenderObjectWidget {
  WizardButtons({
    super.key,
    required Widget previous,
    required Widget label,
    required Widget next,
  }) : super(
          children: [
            LayoutId(
              id: 'previous',
              child: previous,
            ),
            LayoutId(
              id: 'label',
              child: label,
            ),
            LayoutId(
              id: 'next',
              child: next,
            ),
          ],
        );

  @override
  RenderObject createRenderObject(BuildContext context) =>
      RenderWizardButtons();
}

class RenderWizardButtons extends RenderBox
    with
        ContainerRenderObjectMixin<RenderBox, MultiChildLayoutParentData>,
        RenderBoxContainerDefaultsMixin<RenderBox, MultiChildLayoutParentData> {
  @override
  void setupParentData(RenderBox child) {
    if (child.parentData is! MultiChildLayoutParentData) {
      child.parentData = MultiChildLayoutParentData();
    }
  }

  @override
  void performLayout() {
    final idToChild = getChildrenIdMap();

    Size layoutChild(Object key, BoxConstraints constraints) {
      final box = idToChild[key]!;
      box.layout(constraints, parentUsesSize: true);
      return box.size;
    }

    void positionChild(Object key, Offset position) {
      final box = idToChild[key]!;
      (box.parentData as MultiChildLayoutParentData).offset = position;
    }

    final heightConstraint = BoxConstraints.loose(
      Size(double.infinity, constraints.maxHeight),
    );

    final previousIntrinsicWidth = idToChild['previous']! //
        .getMaxIntrinsicWidth(constraints.maxHeight);
    final nextIntrinsicWidth = idToChild['next']! //
        .getMaxIntrinsicWidth(constraints.maxHeight);
    final buttonWidth = (previousIntrinsicWidth > nextIntrinsicWidth)
        ? previousIntrinsicWidth
        : nextIntrinsicWidth;

    final buttonConstraint = BoxConstraints(
      minWidth: buttonWidth,
      maxWidth: buttonWidth,
    );
    final previousSize = layoutChild('previous', buttonConstraint);
    final nextSize = layoutChild('next', buttonConstraint);

    final width = constraints.maxWidth;
    final height = (previousSize.height > nextSize.height)
        ? previousSize.height
        : nextSize.height;

    final rect = Offset.zero & Size(width, height);

    final labelSize = layoutChild('label', heightConstraint);

    positionChild(
      'previous',
      Alignment.centerLeft.inscribe(previousSize, rect).topLeft,
    );
    positionChild(
      'label',
      Alignment.center.inscribe(labelSize, rect).topLeft,
    );
    positionChild(
      'next',
      Alignment.centerRight.inscribe(nextSize, rect).topLeft,
    );

    size = Size(constraints.maxWidth, height);
  }

  Map<Object, RenderBox> getChildrenIdMap() {
    final idToChild = <Object, RenderBox>{};
    RenderBox? child = firstChild;
    while (child != null) {
      final childParentData = child.parentData! as MultiChildLayoutParentData;
      idToChild[childParentData.id!] = child;
      child = childParentData.nextSibling;
    }
    return idToChild;
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    defaultPaint(context, offset);
  }

  @override
  bool hitTestChildren(BoxHitTestResult result, {required Offset position}) {
    return defaultHitTestChildren(result, position: position);
  }
}