Local keys

local_keys.dart

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

// stateless elements scheme 
// https://hsto.org/webt/ha/dh/vy/hadhvybi_mhjvuwdiiucmmx2w6i.gif

// stateful elements before tile swap 
// https://hsto.org/webt/dh/ay/sh/dhayshomjpkfv7b45fxmx1ecduw.gif

// stateful elements after tile swap 
// https://hsto.org/webt/nu/yw/ah/nuywahtbnrv2bfvrwb0osfj1fye.gif

void main() => runApp(new MaterialApp(home: PositionedTiles()));

Color getRandomColor() {
  return Colors.primaries[Random().nextInt(Colors.primaries.length)];
}

class PositionedTiles extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => PositionedTilesState();
}

class PositionedTilesState extends State<PositionedTiles> {
  List<Widget> tiles = [
    StatelessColorfulTile(),
    StatelessColorfulTile(),
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Row(children: tiles),
      floatingActionButton: FloatingActionButton(
          child: Icon(Icons.sentiment_very_satisfied), onPressed: swapTiles),
    );
  }

  swapTiles() {
    setState(() {
      tiles.insert(1, tiles.removeAt(0));
    });
  }
}

class StatelessColorfulTile extends StatelessWidget {
  final Color myColor = getRandomColor();
  @override
  Widget build(BuildContext context) {
    return Container(
        color: myColor, child: Padding(padding: EdgeInsets.all(70.0)));
  }

  static Color getRandomColor() {
    return Colors.primaries[Random().nextInt(Colors.primaries.length)];
  }
}

class StatefulColorfulTile extends StatefulWidget {
  @override
  ColorfulTileState createState() => ColorfulTileState();
}

class ColorfulTileState extends State<StatefulColorfulTile> {
  Color myColor;

  @override
  void initState() {
    super.initState();
    myColor = _getRandomColor();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      color: myColor,
      child: Padding(
        padding: EdgeInsets.all(70.0),
      ),
    );
  }
}