For a SO question

main.dart

class _MyHomePageState extends State<MyHomePage>
    with SingleTickerProviderStateMixin {
  int theirGroupValue = 0;

  List data = List();
  var data1 = [];
  var data2 = [];
  var data3 = [];

  String url = 'https://e19f7c9d.ngrok.io/api/events/westernaf/packages';
  Future<String> makeRequest() async {
    var response = await http
        .get(Uri.encodeFull(url), headers: {"Accept": "application/json"});
    setState(() {
      var extractdata = json.jsonDecode(response.body);
      data = extractdata["result"];
    });
    for (var i = 0; i < data.length; i++) {
      var startTime = data[i]['start_date'].split('T')[0];
      var endTime = data[i]['end_date'].split('T')[0];
      final todayDate = DateTime.now();
      final pkgStartDate = DateTime.parse(startTime);
      final pkgEndDate = DateTime.parse(endTime);
      final difDate = todayDate.isAfter(pkgStartDate);
      final difDate2 = todayDate.isBefore(pkgEndDate);
      if (difDate && difDate2 == true) {
        if (data[i]['regTypeId'] == 1) {
          this.theirGroupValue = 0;
        } else if (data[i]['regTypeId'] == 2) {
          this.theirGroupValue = 1;
        } else if (data[i]['regTypeId'] == 3) {
          this.theirGroupValue = 2;
        } else {
          this.theirGroupValue = 0;
        }
      }
    }

    data1 = data.where((d) => d['regTypeId'] == 1).toList();
    data2 = data.where((d) => d['regTypeId'] == 2).toList();
    data3 = data.where((d) => d['regTypeId'] == 3).toList();
  }

  final Map<int, Widget> logoWidgets = const <int, Widget>{
    0: Text('Early Bird'),
    1: Text('General'),
    2: Text('Onsite'),
  };

  List<bool> inputs = new List<bool>();

  @override
  void initState() {
    super.initState();
    this.makeRequest();
    setState(() {
      for (int i = 0; i < 35; i++) {
        inputs.add(false);
      }
    });
  }

  void ItemChange(bool val, int index) {
    setState(() {
      inputs[index] = val;
    });
  }

  static Widget giveCenter(String ListView) {
    return new Card(
      // child Container(
      child: Text(
        "Text: $ListView",
        style: TextStyle(color: Colors.blue, fontSize: 20.0),
        // )
      ),
    );
  }

  void _Register() {
    print('supposed to push a route');
  }

  @override
  Widget _listingShow(i) {
    var startTime = data1[i]['start_date'].split('T')[0];
    var endTime = data1[i]['end_date'].split('T')[0];
    final todayDate = DateTime.now();
    final pkgStartDate = DateTime.parse(startTime);
    final pkgEndDate = DateTime.parse(endTime);
    final difDate = todayDate.isAfter(pkgStartDate);
    final difDate2 = todayDate.isBefore(pkgEndDate);
    if (difDate && difDate2 == true) {
      return new Row(
        children: <Widget>[
          Expanded(
            child: Text(data1[i]["packageName"]),
          ),
          Expanded(
            child: Text((data1[i]["price"]).toString()),
          ),
          Expanded(
            child: Checkbox(
              value: inputs[i],
              onChanged: (bool val) {
                ItemChange(val, i);
              },
            ),
          ),
        ],
      );
    }
  }

  @override
  Widget _listingShow2(i) {
    var startTime = data2[i]['start_date'].split('T')[0];
    var endTime = data2[i]['end_date'].split('T')[0];
    final todayDate = DateTime.now();
    final pkgStartDate = DateTime.parse(startTime);
    final pkgEndDate = DateTime.parse(endTime);
    final difDate = todayDate.isAfter(pkgStartDate);
    final difDate2 = todayDate.isBefore(pkgEndDate);
    if (difDate && difDate2 == true) {
      return new Row(
        children: <Widget>[
          Expanded(
            child: Text(data2[i]["packageName"]),
          ),
          Expanded(
            child: Text((data2[i]["price"]).toString()),
          ),
          Expanded(
            child: Checkbox(
              value: inputs[i],
              onChanged: (bool val) {
                ItemChange(val, i);
              },
            ),
          ),
        ],
      );
    }
  }

  @override
  Widget _listingShow3(i) {
    var startTime = data3[i]['start_date'].split('T')[0];
    var endTime = data3[i]['end_date'].split('T')[0];
    final todayDate = DateTime.now();
    final pkgStartDate = DateTime.parse(startTime);
    final pkgEndDate = DateTime.parse(endTime);
    final difDate = todayDate.isAfter(pkgStartDate);
    final difDate2 = todayDate.isBefore(pkgEndDate);
    print('$i: ${data3[i]["packageName"]}');
    if (difDate && difDate2 == true) {
      return new Row(
        children: <Widget>[
          Expanded(
            child: Text(data3[i]["packageName"]),
          ),
          Expanded(
            child: Text((data3[i]["price"]).toString()),
          ),
          Expanded(
            child: Checkbox(
              value: inputs[i],
              onChanged: (bool val) {
                ItemChange(val, i);
              },
            ),
          ),
        ],
      );
    }
  }

  Widget build(BuildContext context) {
    List<Widget> bodies = [
      new ListView.builder(
        itemCount: data1.length,
        itemBuilder: (BuildContext context, i) {
          return ListTile(
            title: _listingShow(i),
          );
        },
      ),
      new ListView.builder(
        itemCount: data2.length,
        itemBuilder: (BuildContext context, i) {
          return ListTile(
            title: _listingShow2(i),
          );
        },
      ),
      new ListView.builder(
        itemCount: data3.length,
        itemBuilder: (BuildContext context, i) {
          return ListTile(
            title: _listingShow3(i),
          );
        },
      ),
    ];

    return Scaffold(
      appBar: AppBar(
        elevation: 2.0,
        backgroundColor: Colors.white,
        centerTitle: true,
        title: Text(
          'Select conference Package',
          style: TextStyle(color: Colors.black),
        ),
        bottom: PreferredSize(
          preferredSize: Size(double.infinity, 45.0),
          child: Padding(
            padding: EdgeInsets.only(top: 5.0, bottom: 10.0),
            child: Row(
              children: <Widget>[
                SizedBox(
                  width: 15.0,
                ),
                Expanded(
                  child: CupertinoSegmentedControl(
                    groupValue: this.theirGroupValue,
                    onValueChanged: (changeFromGroupValue) {
                      setState(() {
                        theirGroupValue = this.theirGroupValue;
                      });
                    },
                    children: logoWidgets,
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
      body: bodies[this.theirGroupValue],
    );
  }
}