Flutter - Saving Files

When I need to store small amounts of data, I use shared_preferences. I encode the Dart objects into json before storing and decode on retrieval.

To save an object, encode it to json. To save a List of objects, encode the whole list. You can choose whether to save unlike objects together or separately.

When the list of objects saved changes I simply re-write the whole list.

You should probably start with some simple objects. That way you will find that you can save and read them back pretty easily.

(One of the great things about Dart is that you can run it from the command line. This way you can create and test your data objects first before even including them in a Flutter app. Unit testing is built right into Dart.)

Here's an example of a class that knows how to encode/decode itself as json

class Membership {
  int _index;
  String _name;
  String _id;

  Membership(this._index, this._name, this._id);

  Membership.fromJson(Map<String, dynamic> m) {
    _index = m['index'];
    _name = m['name'];
    _id = m['id'];
  }

  String get id => _id;

  String get name => _name;

  int get index => _index;

  Map<String, dynamic> toJson() => {
        'index': _index,
        'name': _name,
        'id': _id,
      };
}

If you have a List of memberships you persist it like this

List<Membership> memberships = [];
final String membershipKey = 'someuniquestring'; // maybe use your domain + appname
SharedPreferences sp = await SharedPreferences.getInstance();
sp.setString(membershipKey, json.encode(memberships));

and retrieve it like this

memberships = [];
json
    .decode(sp.getString(membershipKey))
    .forEach((map) => memberships.add(new Membership.fromJson(map)));
// don't forget to call setState((){}) to update the Widgets