samplesolution.dart

Future<List> _getAllEvents(String lectid) async {
  var url = "http://www.71slabsolution.com/appointmy/geteventslect.php";

  final response = await http.post(url, body: {
    "useridval": lectid.toString(),
  });

  List<Map> jsonData = json.decode(response.body);
  List<Event> events = jsonData.map((data) => Event.fromJson(data));
  Map<DateTime, List<String>> eventMap = {};
  events.forEach((Event event) {
    DateTime dateTime = DateTime.parse(event.eVTDT);

    if (eventMap[dateTime] == null) {
      eventMap[dateTime] = [event.eVTDETS];
    } else {
      eventMap[dateTime].add(event.eVTDETS);
    }
  });
  
  return events;
}

class Event {
  String mSG;
  String eVTID;
  String iDUSER;
  String eVTDETS;
  String eVTDT;
  String eVTTIMEFROM;
  String eVTTIMETO;
  String eVTSTAT;

  Event(
      {this.mSG,
      this.eVTID,
      this.iDUSER,
      this.eVTDETS,
      this.eVTDT,
      this.eVTTIMEFROM,
      this.eVTTIMETO,
      this.eVTSTAT});

  Event.fromJson(Map<String, dynamic> json) {
    mSG = json['MSG'];
    eVTID = json['EVTID'];
    iDUSER = json['IDUSER'];
    eVTDETS = json['EVT_DETS'];
    eVTDT = json['EVT_DT'];
    eVTTIMEFROM = json['EVT_TIME_FROM'];
    eVTTIMETO = json['EVT_TIME_TO'];
    eVTSTAT = json['EVT_STAT'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['MSG'] = this.mSG;
    data['EVTID'] = this.eVTID;
    data['IDUSER'] = this.iDUSER;
    data['EVT_DETS'] = this.eVTDETS;
    data['EVT_DT'] = this.eVTDT;
    data['EVT_TIME_FROM'] = this.eVTTIMEFROM;
    data['EVT_TIME_TO'] = this.eVTTIMETO;
    data['EVT_STAT'] = this.eVTSTAT;
    return data;
  }
}