Map<String, dynamic> userDetails = {};

  Future<Null> getUser() async {
    await Firestore.instance
        .collection('users') // Your Collections Name
        .document(currentUserId)  // Your user Document Name
        .get()
        .then((val) {
      userDetails.addAll(val.data);
    }).whenComplete(() {
      print('Data Fetched');
      setState(() {});
    });
  }