Intrinsic Height of just the favorite child of a row

main.dart

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

// What I 'm trying to do:

//Mostly just use the intrinsic height of the workspace as the height of the row, and the checklist should just scroll if it doesn't have enough height.

// 10 items in checklist, workspace set to height 200.  The row height should be 200, and the checklist should be scrollable.

// 10 items in the checklist, workspace set to 100. Row height is 200, checklist is scrollable.

// nice to have: 2 items in checklist, workspace set to 100.  Row height is 100

//It seems like if I could wrap the checklist in something to override or limit what it reports for it's intrinsic height. This would all work.

// I started down the MultiChildRenderObjectWidget route, and maybe that's the solution... but I got a little lost.

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.start,
                            children: <Widget>[
                              LimitedBox(
                                //Instead of a limited box, this is where I want a widget that can override or limit the intrinsic height of it's child. The checklist is scrollable
                                child: Checklist(),
                                maxHeight: 200,
                              ),
                              WorkArea(),
                              //Could ideally remove this sized box
                              SizedBox(
                                height: 200,
                              )
                            ],
                          ),
                        ),
                      ),
                    ],
                  ),
                ),
              ),
            ),
          ),
        ),
      ),
    );
  }
}

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

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

class _ChecklistState extends State<Checklist> {
  int _numberOfItems = 10;
  @override
  Widget build(BuildContext context) {
    return LimitedBox(
      maxHeight: 100,
      child: SingleChildScrollView(
        child: Column(
          children: [
            Row(
              children: [
                ElevatedButton(
                    onPressed: () {
                      adjustItemCount(-1);
                    },
                    child: const Text("-")),
                Text(_numberOfItems.toString()),
                ElevatedButton(
                    onPressed: () {
                      adjustItemCount(1);
                    },
                    child: const Text("+")),
              ],
            ),
            ...List.filled(
              _numberOfItems,
              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) {},
                    ),
                  ),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }

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

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

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

class _WorkAreaState extends State<WorkArea> {
  double _height = 200;
  @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("+")),
            ],
          )),
    );
  }

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

//
class RowV2 extends MultiChildRenderObjectWidget {
  const RowV2(
      {required super.children, this.careAboutHeightIndex = 0, super.key});

  final int careAboutHeightIndex;

  @override
  RenderObject createRenderObject(BuildContext context) {
    return RenderRowV2(careAboutHeightIndex: 1);
  }
}

class _RowV2Child extends ContainerBoxParentData<RenderBox>
    with ContainerParentDataMixin<RenderBox> {}

mixin ContainerParentDataMixin<ChildType extends RenderObject> on ParentData {
  /// The previous sibling in the parent's child list.
  ChildType? previousSibling;

  /// The next sibling in the parent's child list.
  ChildType? nextSibling;
}

class RenderRowV2 extends RenderBox
    with
        ContainerRenderObjectMixin<RenderBox, _RowV2Child>,
        RenderBoxContainerDefaultsMixin<RenderBox, _RowV2Child> {
  //The index of our favorite child, the one who's intrinsic height we will use.
  final int careAboutHeightIndex;

  RenderRowV2({required this.careAboutHeightIndex});

  @override
  void setupParentData(covariant RenderObject child) {
    child.parentData = _RowV2Child();
  }

  @override
  void performLayout() {
    var childConstraints = constraints;

    final child = getChildrenAsList().elementAtOrNull(careAboutHeightIndex);

    //The rest of this is just copied code from an example of MultiChildRenderObjectWidget,
    // if (child != null) {
    //   child.layout(constraints, parentUsesSize: true);
    //   childConstraints = BoxConstraints.tight(child.size);
    // }
    //
    // final overlay = (child == null) ? null : childAfter(child);
    // if (overlay != null) {
    //   overlay.layout(childConstraints, parentUsesSize: true);
    // }
    //
    // size = child?.size ?? overlay?.size ?? constraints.smallest;
  }
}