samples/material_3_demo/lib/src/one_two_transition.dart

// Copyright 2021 The Flutter team. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/material.dart';

import 'animations.dart';
import 'constants.dart';

class OneTwoTransition extends StatefulWidget {
  const OneTwoTransition({
    super.key,
    required this.animation,
    required this.one,
    required this.two,
  });

  final Animation<double> animation;
  final Widget one;
  final Widget two;

  @override
  State<OneTwoTransition> createState() => _OneTwoTransitionState();
}

class _OneTwoTransitionState extends State<OneTwoTransition> {
  late final Animation<Offset> offsetAnimation;
  late final Animation<double> widthAnimation;

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

    offsetAnimation = Tween<Offset>(
      begin: const Offset(1, 0),
      end: Offset.zero,
    ).animate(OffsetAnimation(widget.animation));

    widthAnimation = Tween<double>(
      begin: 0,
      end: mediumWidthBreakpoint,
    ).animate(SizeAnimation(widget.animation));
  }

  @override
  Widget build(BuildContext context) {
    return Row(
      children: <Widget>[
        Flexible(flex: mediumWidthBreakpoint.toInt(), child: widget.one),
        if (widthAnimation.value.toInt() > 0) ...[
          Flexible(
            flex: widthAnimation.value.toInt(),
            child: FractionalTranslation(
              translation: offsetAnimation.value,
              child: widget.two,
            ),
          ),
        ],
      ],
    );
  }
}