Flutter how to save list data locally - json

Question

I am building a to-do list app and I would like to store the data locally such that every time I open the app, I get all the tasks that I had created previously. I am new to flutter and this is my first app. I already tried saving the data to a file, creating a JSON file to save the data and tried using a database. Nothing seems to work. Can someone help me with this?
This is my code: -
import 'package:flutter/material.dart';
class toDoList extends StatefulWidget
{
bool data = false;
#override
createState()
{
return new toDoListState();
}
}
class toDoListState extends State<toDoList>
{
List<String> tasks = [];
List<bool> completedTasks = [];
List<String> descriptions = [];
List<bool> importance = [];
#override
Widget build(BuildContext context)
{
return new Scaffold
(
body: buildToDoList(),
floatingActionButton: new FloatingActionButton
(
onPressed: addToDoItemScreen,
tooltip: 'Add Task',
child: new Icon(Icons.add),
),
);
}
Widget buildToDoList()
{
return new ListView.builder
(
itemBuilder: (context, index)
{
if(index < tasks.length)
{
if(tasks[index] == "#45jiodg{}}{OHU&IEB")
{
tasks.removeAt(index);
descriptions.removeAt(index);
importance.removeAt(index);
}
return row(tasks[index], descriptions[index], index);
};
},
);
}
Widget row(String task, String description, int index)
{
return Dismissible(
key: UniqueKey(),
background: Container(color: Colors.red, child: Align(alignment: Alignment.center, child: Text('DELETE', textAlign: TextAlign.center, style: TextStyle(color: Colors.white, fontSize: 18),))),
direction: DismissDirection.horizontal,
onDismissed: (direction) {
setState(() {
tasks.removeAt(index);
if(completedTasks[index])
{
completedTasks.removeAt(index);
}
descriptions.removeAt(index);
importance.removeAt(index);
});
Scaffold.of(context).showSnackBar(SnackBar(content: Text(task+" dismissed")));
},
child: CheckboxListTile(
controlAffinity: ListTileControlAffinity.leading,
title: Text(task, style: (completedTasks[index]) ? TextStyle(decoration: TextDecoration.lineThrough) : TextStyle(),),
subtitle: Text(descriptions[index], style: (completedTasks[index]) ? TextStyle(decoration: TextDecoration.lineThrough) : TextStyle(),),
isThreeLine: true,
secondary: (importance[index])? Icon(Icons.error, color: Colors.red,) : Text(''),
value: completedTasks[index],
onChanged: (bool value) {
setState(() {
if(completedTasks[index])
{
completedTasks[index] = false;
}
else
{
completedTasks[index] = true;
}
});
},
));
}
void addToDoItemScreen() {
int index = tasks.length;
while (importance.length > tasks.length) {
importance.removeLast();
}
importance.add(false);
tasks.add("#45jiodg{}}{OHU&IEB");
descriptions.add("No Description");
completedTasks.add(false);
Navigator.of(context).push(new MaterialPageRoute(builder: (context) {
return StatefulBuilder(builder: (context, setState) { // this is new
return new Scaffold(
appBar: new AppBar(title: new Text('Add a new task')),
body: Form(
child: Column(
children: <Widget>[
TextField(
autofocus: true,
onSubmitted: (name) {
addToDoItem(name);
//Navigator.pop(context); // Close the add todo screen
},
decoration: new InputDecoration(
hintText: 'Enter something to do...',
contentPadding: const EdgeInsets.all(20.0),
border: OutlineInputBorder()),
),
TextField(
//autofocus: true,
//enabled: descriptions.length > desc,
onSubmitted: (val) {
addDescription(val, index);
},
decoration: new InputDecoration(
hintText: 'Enter a task decription...',
contentPadding: const EdgeInsets.all(20.0),
border: OutlineInputBorder()),
),
Row(
children: <Widget> [
Switch(
value: importance[index],
onChanged: (val) {
setState(() {
});
impTask(index);
},
),
Text('Important Task', style: TextStyle(fontSize: 18)),
],
),
RaisedButton(onPressed: () { Navigator.pop(context); }, child: Text('DONE', style: TextStyle(fontSize: 20)),)
],
),
));
});
}));
}
void addToDoItem(String task)
{
setState(() {
tasks.last = task;
});
}
void addDescription(String desc, int index)
{
setState(() {
descriptions.last = desc;
});
}
void impTask(int index)
{
setState(() {
if(importance[index])
{
importance[index] = false;
}
else
{
importance[index] = true;
}
});
}
}
I have 4 lists with the data. I need a simple way to save the lists such that the next time I open the app, the lists retain the data that was saved in them, the last time I had closed the app.

Answer 1

To do this you'll certainly have to use the path_provider package with this tutorial on the flutter.dev website. You should then be able to register a file and read it at the start of your application.
Once you have imported the path_provider and the dart:io packages, you can do something like this :
final directory = await getApplicationDocumentsDirectory();
final File file = File('${directory.path}/jsonObjects.json');
if (await file.exists()) {
json = await file.readAsString();
} else {
file.writeAsString(json);
}
First you get the application document directory ( the path ), then you create a File with the right path. Then if the file already exist, you read it, else you create it with the json you got and you should be good to go !