hash-wallet/lib/src/widgets/adaptable_page_view.dart

import 'dart:ui';

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

const _firstLayoutMaxHeight = 10000.0;

class PageViewHeightAdaptable extends StatefulWidget {
  const PageViewHeightAdaptable({
    super.key,
    required this.controller,
    required this.children,
  }) : assert(children.length > 0, 'children must not be empty');

  final PageController controller;
  final List<Widget> children;

  @override
  State<PageViewHeightAdaptable> createState() => _PageViewHeightAdaptableState();
}

class _PageViewHeightAdaptableState extends State<PageViewHeightAdaptable> {
  final _sizes = <int, Size>{};

  @override
  void didUpdateWidget(PageViewHeightAdaptable oldWidget) {
    super.didUpdateWidget(oldWidget);

    _sizes.clear();
  }

  @override
  Widget build(BuildContext context) {
    return ListenableBuilder(
      listenable: widget.controller,
      builder: (context, child) => _SizingContainer(
        sizes: _sizes,
        page: widget.controller.hasClients ? widget.controller.page ?? 0 : 0,
        child: child!,
      ),
      child: LayoutBuilder(
        builder: (context, constraints) => PageView(
          controller: widget.controller,
          children: [
            for (final (i, child) in widget.children.indexed)
              Stack(
                alignment: Alignment.topCenter,
                clipBehavior: Clip.hardEdge,
                children: [
                  SizedBox.fromSize(size: _sizes[i]),
                  Positioned(
                    left: 0,
                    top: 0,
                    right: 0,
                    child: _SizeAware(
                      child: child,
                      // don't setState, we'll use it in the layout phase
                      onSizeLaidOut: (size) {
                        _sizes[i] = size;
                      },
                    ),
                  ),
                ],
              ),
          ],
        ),
      ),
    );
  }
}

typedef _OnSizeLaidOutCallback = void Function(Size);

class _SizingContainer extends SingleChildRenderObjectWidget {
  const _SizingContainer({
    super.child,
    required this.sizes,
    required this.page,
  });

  final Map<int, Size> sizes;
  final double page;

  @override
  _RenderSizingContainer createRenderObject(BuildContext context) {
    return _RenderSizingContainer(
      sizes: sizes,
      page: page,
    );
  }

  @override
  void updateRenderObject(
    BuildContext context,
    _RenderSizingContainer renderObject,
  ) {
    renderObject
      ..sizes = sizes
      ..page = page;
  }
}

class _RenderSizingContainer extends RenderProxyBox {
  _RenderSizingContainer({
    RenderBox? child,
    required Map<int, Size> sizes,
    required double page,
  })  : _sizes = sizes,
        _page = page,
        super(child);

  Map<int, Size> _sizes;
  Map<int, Size> get sizes => _sizes;
  set sizes(Map<int, Size> value) {
    if (_sizes == value) return;
    _sizes = value;
    markNeedsLayout();
  }

  double _page;
  double get page => _page;
  set page(double value) {
    if (_page == value) return;
    _page = value;
    markNeedsLayout();
  }

  @override
  void performLayout() {
    if (child case final child?) {
      child.layout(
        constraints.copyWith(
          minWidth: constraints.maxWidth,
          minHeight: 0,
          maxHeight: constraints.hasBoundedHeight ? null : _firstLayoutMaxHeight,
        ),
        parentUsesSize: true,
      );

      final int floorPage = page.floor();
      final int ceilPage = page.ceil();

      Size? a = sizes[floorPage];
      Size? b = sizes[ceilPage];

      if (a == null && sizes.isNotEmpty) {
        a = sizes.values.first;
      }
      if (b == null && sizes.isNotEmpty) {
        b = sizes.values.first;
      }

      a ??= child.getDryLayout(constraints);
      b ??= a;

      final double t = (page - floorPage).clamp(0.0, 1.0);
      final double height = lerpDouble(a.height, b.height, t) ?? a.height;

      child.layout(
        constraints.copyWith(minHeight: height, maxHeight: height),
        parentUsesSize: true,
      );
      size = child.size;
    } else {
      size = computeSizeForNoChild(constraints);
    }
  }
}

class _SizeAware extends SingleChildRenderObjectWidget {
  const _SizeAware({
    required Widget child,
    required this.onSizeLaidOut,
  }) : super(child: child);

  final _OnSizeLaidOutCallback onSizeLaidOut;

  @override
  _RenderSizeAware createRenderObject(BuildContext context) {
    return _RenderSizeAware(
      onSizeLaidOut: onSizeLaidOut,
    );
  }

  @override
  void updateRenderObject(BuildContext context, _RenderSizeAware renderObject) {
    renderObject.onSizeLaidOut = onSizeLaidOut;
  }
}

class _RenderSizeAware extends RenderProxyBox {
  _RenderSizeAware({
    RenderBox? child,
    required _OnSizeLaidOutCallback onSizeLaidOut,
  })  : _onSizeLaidOut = onSizeLaidOut,
        super(child);

  _OnSizeLaidOutCallback? _onSizeLaidOut;
  _OnSizeLaidOutCallback get onSizeLaidOut => _onSizeLaidOut!;
  set onSizeLaidOut(_OnSizeLaidOutCallback value) {
    if (_onSizeLaidOut == value) return;
    _onSizeLaidOut = value;
    markNeedsLayout();
  }

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

    onSizeLaidOut(
      getDryLayout(
        constraints.copyWith(maxHeight: double.infinity),
      ),
    );
  }
}