samples/animations/lib/src/misc/animated_switcher.dart

// Copyright 2020 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 'dart:math';

import 'package:flutter/material.dart';

Color generateColor() => Color(0xFFFFFFFF & Random().nextInt(0xFFFFFFFF));

Widget generateContainer(int keyCount) => Container(
  key: ValueKey<int>(keyCount),
  height: Random().nextDouble() * 200,
  width: Random().nextDouble() * 200,
  decoration: BoxDecoration(
    color: generateColor(),
    borderRadius: BorderRadius.circular(Random().nextDouble() * 100),
    border: Border.all(
      color: generateColor(),
      width: Random().nextDouble() * 5,
    ),
  ),
);

class AnimatedSwitcherDemo extends StatefulWidget {
  const AnimatedSwitcherDemo({super.key});
  static String routeName = 'misc/animated_switcher';

  @override
  State<AnimatedSwitcherDemo> createState() => _AnimatedSwitcherDemoState();
}

class _AnimatedSwitcherDemoState extends State<AnimatedSwitcherDemo> {
  late Widget container;
  late int keyCount;

  @override
  void initState() {
    super.initState();
    keyCount = 0;
    container = generateContainer(keyCount);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('AnimatedSwitcher'),
        actions: [
          TextButton(
            onPressed:
                () => setState(() => container = generateContainer(++keyCount)),
            child: const Text('Change Widget'),
          ),
        ],
      ),
      body: Center(
        // AnimatedSwitcher Widget is used to switch between different widgets
        // with a given transition. You can change the transitions by using
        // transitionBuilder property.
        child: AnimatedSwitcher(
          duration: const Duration(seconds: 1),
          child: container,
          transitionBuilder:
              (child, animation) =>
                  ScaleTransition(scale: animation, child: child),
        ),
      ),
    );
  }
}