StreamBuilder

Widget build(BuildContext context) {
    return StreamBuilder(
      stream: Firestore.instance.collection("categories_item").snapshots(),
      builder: (context, snapshot) {
        if (!snapshot.hasData) {
          return Center(
            child: CircularProgressIndicator(
              valueColor: AlwaysStoppedAnimation<Color>(redMaroon),
            ),
          );
        } else {
          return Scaffold(
            backgroundColor: Color(0xFFFCFAF8),
            body: ListView(
              children: <Widget>[
                Container(
                  padding: EdgeInsets.only(right: 15.0),
                  width: MediaQuery.of(context).size.width - 30.0,
                  height: MediaQuery.of(context).size.height - 50.0,
                  child: GridView.count(
                    crossAxisCount: 2,
                    primary: false,
                    crossAxisSpacing: 10.0,
                    mainAxisSpacing: 15.0,
                    childAspectRatio: 0.8,
                    children: snapshot.data.documents.map<Widget>((document) {
                      return _buildCardItem(
                        context,
                        document,
                        false,
                        'assets/burger.jpg',
                        false,
                      );
                    }).toList(),
                  ),
                )
              ],
            ),
          );
        }
      },
    );
  }