smooth-app/packages/smooth_app/lib/widgets/widget_height.dart

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

class MeasureSize extends SingleChildRenderObjectWidget {
  const MeasureSize({
    super.key,
    required this.onChange,
    required Widget super.child,
  });

  final OnWidgetSizeChange onChange;

  @override
  RenderObject createRenderObject(BuildContext context) {
    return MeasureSizeRenderObject(onChange);
  }

  @override
  void updateRenderObject(
    BuildContext context,
    covariant MeasureSizeRenderObject renderObject,
  ) {
    renderObject.onChange = onChange;
  }
}

class MeasureSizeRenderObject extends RenderProxyBox {
  MeasureSizeRenderObject(this.onChange);

  OnWidgetSizeChange onChange;
  Size? oldSize;

  @override
  void performLayout() {
    super.performLayout();

    final Size newSize = child!.size;
    if (oldSize != newSize) {
      oldSize = newSize;
      WidgetsBinding.instance.addPostFrameCallback((_) {
        onChange(newSize);
      });
    }
  }
}

typedef OnWidgetSizeChange = void Function(Size size);