How to decode JSON to a Map<DateTime, List<Object>> - json

Question

I can't figure out how to decode a JSON to a specific Map.
First of all I have a map that stores the date as the map key, and the value is a list of objects.
I also made custom methods to convert the objects to JSON.
The class model for the list of objects is:
class Task {
late int taskId;
late bool isCompleted;
late String text;
late PriorityItem priority;
Map<String, dynamic> toJson() =>
{
"id": taskId,
"isCompleted": isCompleted,
"text": text,
"priority": priority.toString(),
};
factory Task.fromJson(Map<String, dynamic> json) =>
Task(
json["isCompleted"],
taskId:json["id"],
text: json["text"],
priority: json["priority"]);
}
enum PriorityItem{
low,
medium,
high
}
The map is stored inside another class called TaskList as
static LinkedHashMap<DateTime, List<Task>> weeklyTaskMap = LinkedHashMap<DateTime, List<Task>>();
static Map<String, dynamic> toJson(LinkedHashMap<DateTime, List<Task>> taskMap) {
Map<String, dynamic> myMap = {};
taskMap.forEach((key, value) {
myMap[key.toIso8601String()] = List<dynamic>.from(value.map((x) => x.toJson()));
});
return myMap;
}
static LinkedHashMap<DateTime, List<Task>> fromJson(Map<String, dynamic> json) {
LinkedHashMap<DateTime, List<Task>> myMap = {} as LinkedHashMap<DateTime, List<Task>>;
json.forEach((key, value) {
myMap[DateTime.parse(key)] = List<Task>.from(json[value]
.map((x) => Task.fromJson(value)));
});
return myMap;
}
Encoding the map to JSON is working just fine, this would be an output after encoding the map:
{
"2022-11-14T15:38:52.879009": [
{
"id": 0,
"isCompleted": false,
"text": "how to get rid ",
"priority": "PriorityItem.medium"
},
{
"id": 1,
"isCompleted": false,
"text": "good morning and I ",
"priority": "PriorityItem.low"
}
],
"2022-11-15T00:00:00.000Z": [
{
"id": 2,
"isCompleted": false,
"text": "how to get rid of the ",
"priority": "PriorityItem.high"
}
]
}
Methods used to encode and decode:
void getMapsFromPrefs() async {
SharedPreferences getMaps = await _prefs;
Map dailyMap = TaskList.fromJson(jsonDecode(getMaps.getString('daily')!));
LinkedHashMap<DateTime, List<Task>> weeklyMap = jsonDecode(getMaps.getString('weekly')!);
TaskList.taskMap = dailyMap;
TaskList.weeklyTaskMap = weeklyMap;
}
void saveMapsToPrefs() async {
SharedPreferences getMaps = await _prefs;
getMaps.clear();
var dailyTasksJson = json.encode(TaskList.toJson(TaskList.taskMap));
var weeklyTasksJson = json.encode(TaskList.toJson(TaskList.weeklyTaskMap));
getMaps.setString('daily', dailyTasksJson);
getMaps.setString('weekly', weeklyTasksJson);
print("saved ${getMaps.getString('daily')}");
}
The only problem I have is decoding the JSON to my desired Map.
I hope this is understandable, if anyone needs extra information please feel free to ask :)
Thank you.

Answer 1

A possible quick fix could be updating your .fromJSON class method, it looks like you forgot the isCompleted field.
factory Task.fromJson(Map<String, dynamic> json) =>
Task(
isCompleted: json["isCompleted"],
taskId:json["id"],
text: json["text"],
priority: json["priority"]);

Answer 2

The issue was inside the fromJson() function, I was generating the list from an invalid variable
Updated method:
static LinkedHashMap<DateTime, List<Task>> fromJson(Map<String, dynamic> json) {
LinkedHashMap<DateTime, List<Task>> tempMap = LinkedHashMap<DateTime, List<Task>>();
json.forEach((key, value) {
tempMap.addAll({DateTime.parse(key): **List<Task>.from(value.map((x) => Task.fromJson(x)))**
});
});
return tempMap;
}