Flutter Grid example with highlighted square

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MaterialApp(
      debugShowCheckedModeBanner: false, home: Scaffold(body: BoxApp())));
}

class BoxApp extends StatefulWidget {
  @override
  BoxAppState createState() => BoxAppState();
}

class BoxAppState extends State<BoxApp> with SingleTickerProviderStateMixin {
  AnimationController _controller;
  Animation<double> _animation;
  int selectedTileIndex = 0;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
        duration: const Duration(milliseconds: 500), vsync: this);
    _animation = Tween<double>(begin: 0, end: 7).animate(_controller)
      ..addListener(() {
        setState(() {
          if (_animation.isCompleted) {
            _controller.reverse();
          } else if (_animation.value == 0) {
            _controller.forward();
          }
        });
      });
    _controller.forward();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Center(
        child: GridView.count(
            padding: const EdgeInsets.all(10),
            crossAxisCount: 8,
            crossAxisSpacing: 10,
            mainAxisSpacing: 10,
            children: List.generate(
              64,
              (index) => GestureDetector(
                onTap: () {
                  setState(() {
                    selectedTileIndex = index;
                  });
                },
                child: Container(
//                   width: 100,
//                   height: 100,
                  decoration: BoxDecoration(
                    color: Colors.black54,
                    borderRadius: BorderRadius.circular(10),
                    border: Border.all(
                        color: Colors.green,
                        width: index == selectedTileIndex ? _animation.value : 0),
                  ),
                ),
              ),
            )));
  }
}