dynamic_gridview.dart

class _HomeState extends State<Home> {
  final elements = List.generate(10, (index) => index);

  void _onTap() {
    setState(() {
      elements.add(elements.length);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: GridView.builder(
        itemCount: elements.length + 1,
        itemBuilder: (_, index) {
          if (index == elements.length) {
            return GestureDetector(
              onTap: _onTap,
              child: Container(
                child: FittedBox(child: Icon(Icons.add)),
              ),
            );
          }
          return Padding(
            padding: const EdgeInsets.all(5.0),
            child: Container(
              color: Colors.primaries[index % Colors.primaries.length],
              child: FittedBox(
                child: Text(
                  index.toString(),
                ),
              ),
            ),
          );
        },
        gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
          crossAxisCount: 3,
          childAspectRatio: 1,
        ),
      ),
    );
  }
}