When to use keys, part 2 - statefull

main.dart

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

void main() { 
  runApp(new MaterialApp(home: PositionedTiles()));
  

}

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

class PositionedTilesState extends State<PositionedTiles> {
 List<Widget> tiles = [
   StatefulColorfulTile(key: UniqueKey()), // попробуй убрать key: UniqueKey()
   StatefulColorfulTile(key: UniqueKey()), // попробуй убрать key: UniqueKey()
];

 

 @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 StatefulColorfulTile extends StatefulWidget {
 StatefulColorfulTile({Key key}) : super(key: key); // попробуй закоментировать
 @override
 ColorfulTileState createState() => ColorfulTileState();
}

class ColorfulTileState extends State<StatefulColorfulTile> {
 Color myColor;

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

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

class UniqueColorGenerator {
  
  UniqueColorGenerator();
  var randomGenerator = Random();
  List<Color> _listColors = [
    Colors.pinkAccent,
    Colors.brown,
    Colors.green,
    Colors.purple,
    Colors.yellow
  ];
  
  Color getColor() {
    
    return _listColors[randomGenerator.nextInt(4)];
  }
}