added toJson to enum

lib/model/alarm/alarm.dart

@@ -9,12 +9,12 @@ abstract class Alarm {
 
   factory Alarm.fromJson(Map<String, dynamic> json) {
     if (json.containsKey('alarmType')) {
-      switch (json['alarmType'] as String) {
+      switch (AlarmType.fromJson(json['alarmType'])) {
-        case 'timeFixed':
+        case AlarmType.timeFixed:
           return FixedTimeAlarm.fromJson(json);
-        case 'timeRelative':
+        case AlarmType.timeRelative:
           return RelativeTimeAlarm.fromJson(json);
-        case 'location':
+        case AlarmType.location:
           return LocationAlarm.fromJson(json);
       }
     }
@@ -33,4 +33,11 @@ abstract class Alarm {
   int get hashCode => id.hashCode;
 }
 
-enum AlarmType { timeFixed, timeRelative, location }
+enum AlarmType {
+  timeFixed,
+  timeRelative,
+  location;
+
+  String toJson() => name;
+  static AlarmType fromJson(String json) => values.byName(json);
+}