flutter_gridview_tut

.\lib\main.dart

//...
class _MyHomePageState extends State<MyHomePage> {
  _openImage(context, index) async {
    showDialog(
      context: context,
      builder: (a) => AlertDialog(
        title: Text("Look at this! Very Nice!"),
        content: FadeInImage.memoryNetwork(
            placeholder: kTransparentImage, 
            image: 'https://picsum.photos/id/$index/512'),
        actions: <Widget>[
          FlatButton(
              onPressed: () {
                _dismissDialog(context);
              },
              child: Text('Close'))
        ],
      ),
    );
  }
  //...
}