Widget _buildBody(BuildContext context) {
    return StreamBuilder<QuerySnapshot>(
      stream: Firestore.instance.collection("prova").snapshots(),
      builder: (context, snapshot) {
        // if (!snapshot.hasData) return LinearProgressIndicator();
        switch (snapshot.connectionState) {
          case ConnectionState.waiting:
            return new Center(child: new CircularProgressIndicator());
          default:
            return _buildList(context, snapshot.data.documents);
        }
      },
    );
  }

  Widget _buildList(BuildContext context, List<DocumentSnapshot> snapshot) {
   return ListView(
     padding: const EdgeInsets.only(top: 20.0),
     children: snapshot.map((data) => _buildListItem(context, data)).toList(),
   );
  }

    Widget _buildListItem(BuildContext context, DocumentSnapshot data) {
    final record = Record.fromSnapshot(data);
    String name = record.name;
    return Padding(
      key: ValueKey(record.name),
      padding: const EdgeInsets.symmetric(horizontal: 16.0, vertical: 8.0),
      child: Container(
        decoration: BoxDecoration(
          border: Border.all(color: Colors.grey),
          borderRadius: BorderRadius.circular(7.0),
        ),
        child: ListTile(
          title: Text(titolo),
          onTap: (){
            Firestore.instance.collection("prova").document(data.documentID.toString()).delete().catchError((e){
                print(e);
              }
            );
          },
        ),
      ),
    );
  }
}