flutter_firestore_tut

.\lib\scr\home.dart

//...
class _Home extends State<StatefulWidget> {
  //... 
  void interact() async {
    final DocumentReference postRef =
        Firestore.instance.collection('stats').document('interactions');
    await Firestore.instance.runTransaction((Transaction tx) async {
      DocumentSnapshot postSnapshot = await tx.get(postRef);
      if (postSnapshot.exists) {
        await tx.update(postRef,
            <String, dynamic>{'count': postSnapshot.data['count'] + 1});
      }
    });
  }
  //...
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      //...
  }
}