ImplicitAnimations

sample.packages.flutter.lib.src.widgets.implicit_animations.1017.

The following example transitions an AnimatedPositioned between two states. It adjusts the height, width, and [Positioned] properties when tapped.

  
import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: const Center(
          child: MyStatefulWidget(),
        ),
      ),
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

  @override
  State createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State {
  bool selected = false;

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      width: 200,
      height: 350,
      child: Stack(
        children: [
          AnimatedPositioned(
            width: selected ? 200.0 : 50.0,
            height: selected ? 50.0 : 200.0,
            top: selected ? 50.0 : 150.0,
            duration: const Duration(seconds: 2),
            curve: Curves.fastOutSlowIn,
            child: GestureDetector(
              onTap: () {
                setState(() {
                  selected = !selected;
                });
              },
              child: Container(
                color: Colors.blue,
                child: const Center(child: Text('Tap me')),
              ),
            ),
          ),
        ],
      ),
    );
  }
}
  

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