Flutter how to save list data locally

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 !