flutter-app/flutter_app/lib/main.dart

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';
import 'dart:async';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData.dark(),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() {
    return _MyHomePageState();
  }
}

class _MyHomePageState extends State<MyHomePage> {
  final db = Firestore.instance.collection('lots');
  static int lot = 5;
  static int col = 4;

//  Future<List<LotRecord>> getLots(Future<>) async{
//  List<lotRecord> lotList =
//
//    return lotList;
//}
  void getLot(){
    print("pressed");
  }


  @override
  Widget build(BuildContext context) {
    void _swichLayout(){
      setState(() {
        if (col == 2){
          print("col = 2");
          col=4;
        }
        else {
          print("col =" + col.toString());
          col =2;
        }
      });
    }
    void _onItemTapped(int index) {
      getLot();
      setState(() {
        index == 0 ? lot-- : lot++;
      });
    }
    return Scaffold(
      appBar: AppBar(title: Text("Lot Number: " + lot.toString()), centerTitle: true,),
      body:
//      _buildLot(context, db),
      _buildBody(
          context, db.document("Lot" + lot.toString()).collection('stalls'), col),
      bottomNavigationBar: BottomNavigationBar(
//        type: BottomNavigationBarType.shifting ,
        items: <BottomNavigationBarItem>[
          BottomNavigationBarItem(icon: Icon(Icons.arrow_back, color: Colors.white70), title: Text('Last Lot', style: TextStyle(color: Colors.white))),
          BottomNavigationBarItem(icon: Icon(Icons.arrow_forward, color: Colors.white70), title: Text('Next Lot', style: TextStyle(color: Colors.white))),
        ],
        currentIndex: 0,
        fixedColor: Colors.deepPurple,
        onTap: _onItemTapped,
      ),
      floatingActionButton: FloatingActionButton(onPressed: _swichLayout),
    );

  }
}





Widget _(BuildContext context, CollectionReference stallDB, int col) {
  return StreamBuilder<QuerySnapshot>(
    stream: stallDB.snapshots(),
    builder: (context, snapshot) {
      if (!snapshot.hasData) return LinearProgressIndicator();

      return _buildList(context, snapshot.data.documents, col);
    },
  );
}

Widget _buildBody(BuildContext context, CollectionReference stallDB,int col) {
  return StreamBuilder<QuerySnapshot>(
    stream: stallDB.snapshots(),
    builder: (context, snapshot) {
      if (!snapshot.hasData) return LinearProgressIndicator();

      return _buildList(context, snapshot.data.documents,col);
    },
  );
}

Widget _buildList(BuildContext context, List<DocumentSnapshot> snapshot,int col) {
  return GridView.count(
    primary: false,
    padding:  EdgeInsets.all(120/col),
    childAspectRatio: 2/col,
    crossAxisSpacing: 5.0,
    crossAxisCount: col,
    children: snapshot.map((data) => _buildListItem(context, data)).toList(),
  );
}

Widget _buildListItem(BuildContext context, DocumentSnapshot data) {
  final record = Record.fromSnapshot(data);
  return GestureDetector(
  onTap: (){ _showInfo(record,context);},
    child: Card(
    key: ValueKey(record.stall),
    color: (record.open ? Colors.green[200] : Colors.red[100]),
    child: Center(
      child: Column(
        children: [
          ListTile(
            title: Text("Stall " + record.stall.toString(),
                style: TextStyle(fontWeight: FontWeight.w500)),
          ),
        ],
      ),
    ),
    ),
  );
}
//SimpleDialogOption
void _showInfo(Record record, context){
  print("Record # " + record.stall.toString() + " pressed");
  String message = '';
  record.handicap ? message =" is designated for handicap" : message=" is not reserved for handicap";
  AlertDialog alert = new AlertDialog(
      content: Text(
        "Stall # " + record.stall.toString() + message
      ),
    );
  showDialog(context: context, child: alert);
}



class LotRecord {
  final int lot;
  final int col;
  final String name;
  final DocumentReference reference;

  LotRecord.fromMap(Map<String, dynamic> map, {this.reference})
      : assert(map['lot'] != null),
        assert(map['col'] != null),
        assert(map['name'] != null),
        lot = map['lot'],
        col = map['col'],
        name = map['name'];


  LotRecord.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(snapshot.data, reference: snapshot.reference);

  @override
  String toString() => "Record<$lot>";
}


class Record {
  final int stall;
  final int passID;
  final bool open;
  final bool handicap;
  final DocumentReference reference;

  Record.fromMap(Map<String, dynamic> map, {this.reference})
      : assert(map['handicap'] != null),
        assert(map['stall'] != null),
        assert(map['passID'] != null),
        assert(map['open'] != null),
        stall = map['stall'],
        passID = map['passID'],
        open = map['open'],
        handicap = map['handicap'];

  Record.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(snapshot.data, reference: snapshot.reference);

  @override
  String toString() => "Record<$stall>";
}