Force Intrinsics - by Simon Lightfoot - Humpday Q&A :: 12th June 2024 #Flutter #Dart - https://www.youtube.com/watch?v=QBmqKvw_0s8

humpday_2024-06-12_1.dart

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

void main() => runApp(const ExampleApp());

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: SingleChildScrollViewExample(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return DefaultTextStyle(
      style: Theme.of(context).textTheme.bodyMedium!,
      child: ColoredBox(
        color: Colors.white,
        child: Center(
          child: SizedBox(
            height: 400,
            child: Container(
              decoration: BoxDecoration(
                border: Border.all(color: Colors.black),
              ),
              child: SingleChildScrollView(
                child: Padding(
                  padding: const EdgeInsets.all(8.0),
                  child: Column(
                    children: [
                      const Text('Header stuff'),
                      IntrinsicHeight(
                        child: DecoratedBox(
                          decoration: BoxDecoration(
                            border: Border.all(color: Colors.black),
                          ),
                          child: const Row(
                            mainAxisSize: MainAxisSize.min,
                            crossAxisAlignment: CrossAxisAlignment.stretch,
                            children: <Widget>[
                              Expanded(
                                child: Checklist(),
                              ),
                              Expanded(
                                child: WorkArea(),
                              ),
                            ],
                          ),
                        ),
                      ),
                    ],
                  ),
                ),
              ),
            ),
          ),
        ),
      ),
    );
  }
}

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

  @override
  State<Checklist> createState() => _ChecklistState();
}

class _ChecklistState extends State<Checklist> {
  int _numberOfItems = 10;

  void adjustItemCount(int amount) {
    setState(() {
      _numberOfItems = (_numberOfItems + amount) //
          .clamp(0, 100);
    });
  }

  @override
  Widget build(BuildContext context) {
    return ForceIntrinsics(
      width: 0,
      height: 0,
      child: CustomScrollView(
        physics: const ClampingScrollPhysics(),
        slivers: [
          SliverToBoxAdapter(
            child: Row(
              children: [
                ElevatedButton(
                  onPressed: () => adjustItemCount(-1),
                  child: const Text('-'),
                ),
                Text(_numberOfItems.toString()),
                ElevatedButton(
                  onPressed: () => adjustItemCount(1),
                  child: const Text('+'),
                ),
              ],
            ),
          ),
          SliverList(
            delegate: SliverChildBuilderDelegate(
              childCount: _numberOfItems,
              (BuildContext context, int index) {
                return Material(
                  child: Container(
                    color: Colors.red,
                    child: SizedBox(
                      height: 25,
                      width: 100,
                      child: Checkbox(
                        value: false,
                        //Yes, I know they don't work, that's ok for this example.
                        onChanged: (bool? value) {},
                      ),
                    ),
                  ),
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}

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

  @override
  State<WorkArea> createState() => _WorkAreaState();
}

class _WorkAreaState extends State<WorkArea> {
  double _height = 200;

  void adjustHeight(double amount) {
    setState(() {
      _height = (_height + amount).clamp(0, 500);
    });
  }

  @override
  Widget build(BuildContext context) {
    return ColoredBox(
      color: Colors.teal,
      child: SizedBox(
        height: _height,
        child: Row(
          children: [
            ElevatedButton(
              onPressed: () => adjustHeight(-50),
              child: const Text('-'),
            ),
            Text(_height.toString()),
            ElevatedButton(
              onPressed: () => adjustHeight(50),
              child: const Text('+'),
            ),
          ],
        ),
      ),
    );
  }
}

class ForceIntrinsics extends SingleChildRenderObjectWidget {
  const ForceIntrinsics({
    super.key,
    this.width,
    this.height,
    required super.child,
  });

  final double? width;
  final double? height;

  @override
  RenderObject createRenderObject(BuildContext context) {
    return RenderForceIntrinsics(
      width: width,
      height: height,
    );
  }

  @override
  void updateRenderObject(
      BuildContext context, covariant RenderForceIntrinsics renderObject) {
    renderObject
      ..width = width
      ..height = height;
  }
}

class RenderForceIntrinsics extends RenderProxyBox {
  RenderForceIntrinsics({
    double? width,
    double? height,
  })  : _width = width,
        _height = height;

  double? _width;
  double? _height;

  double? get width => _width;

  set width(double? value) {
    if (_width != value) {
      _width = value;
      markNeedsLayout();
    }
  }

  double? get height => _height;

  set height(double? value) {
    if (_height != value) {
      _height = value;
      markNeedsLayout();
    }
  }

  @override
  double getMinIntrinsicHeight(double width) {
    if (_height case double height) {
      return height;
    }
    return super.getMinIntrinsicHeight(width);
  }

  @override
  double getMaxIntrinsicHeight(double width) {
    if (_height case double height) {
      return height;
    }
    return super.getMaxIntrinsicHeight(width);
  }

  @override
  double getMinIntrinsicWidth(double height) {
    if (_width case double width) {
      return width;
    }
    return super.getMinIntrinsicWidth(height);
  }

  @override
  double getMaxIntrinsicWidth(double height) {
    if (_width case double width) {
      return width;
    }
    return super.getMaxIntrinsicWidth(height);
  }
}