Issue
The list which stores the task data is integrated with provider for state management, but once I close the app and reopen it again, all tasks vanish.
With resources, I got to know about SharedPreferences.
How do I go about saving and getting the data using shared preferences. I have given the code a try, but does not seem to work in my favor.
void saveData() async {
final prefs = await SharedPreferences.getInstance();
final String encodedData = Task.encode(tasks);
await prefs.setString('task_data', encodedData);
}
void getData() async {
final prefs = await SharedPreferences.getInstance();
final String taskString = prefs.getString('task_data').toString();
List<Task> tasksData = Task.decode(taskString);
_tasks = tasksData;
}
encode() and decode() functions help in mapping List to String and String to List respectively.
static String encode(List<Task> tasks) {
return jsonEncode(
tasks.map<Map<String, dynamic>>((task) => Task.toMap(task)).toList(),
);
}
static List<Task> decode(String tasks) {
var data = (jsonDecode(tasks) as List<dynamic>?);
if (data != null) {
return (jsonDecode(tasks) as List<dynamic>?)!.map<Task>((task) {
return Task.fromJson(task);
}).toList();
} else {
return <Task>[];
}
}
The Task list in displayed using ListView.
Widget build(BuildContext context) {
return Consumer<TaskData>(
builder: (context, taskData, child) {
taskData.getData();
return ListView.builder(
itemCount: taskData.taskCount,
itemBuilder: (context, index) {
taskData.sortTaskList();
final task = taskData.tasks[index];
return TaskTile(
taskTitle: task.name,
isChecked: task.isDone,
checkboxCallBack: (checkBoxState) async {
taskData.upDateTask(task);
taskData.saveData();
},
longPressCallBack: () async {
taskData.removeTask(task);
taskData.saveData();
},
);
},
);
},
);
}
Solution
I am expecting that you’re using ChangeNotifier
with Provider
package in TaskData
class.
In this case you have to add notifyListener()
inside getData()
because it async task.
Future<void> getData() async {
final prefs = await SharedPreferences.getInstance();
final String taskString = prefs.getString('task_data').toString();
List<Task> tasksData = Task.decode(taskString);
_tasks = tasksData;
notifyListener(); // Add this line
}
Answered By – Usama Karim
Answer Checked By – Marilyn (FlutterFixes Volunteer)