13 Flutter: JSON Storage

main.dart
import 'package:flutter/material.dart';
import 'dart:io';
import 'dart:convert'; //to convert json to maps and vice versa
import 'package:path_provider/path_provider.dart'; //add path provider dart plugin on pubspec.yaml file
​
void main() {
  runApp(new MaterialApp(
    home: new Home(),
  ));
}
​
class Home extends StatefulWidget {
  @override
  State createState() => new HomeState();
}
​
class HomeState extends State<Home> {
​
  TextEditingController keyInputController = new TextEditingController();
  TextEditingController valueInputController = new TextEditingController();
​
  File jsonFile;
  Directory dir;
  String fileName = "myJSONFile.json";
  bool fileExists = false;
  Map<String, String> fileContent; 
​
  @override
  void initState() {
    super.initState();
    /*to store files temporary we use getTemporaryDirectory() but we need
    permanent storage so we use getApplicationDocumentsDirectory() */
    getApplicationDocumentsDirectory().then((Directory directory) {
      dir = directory;
      jsonFile = new File(dir.path + "/" + fileName);
      fileExists = jsonFile.existsSync();
      if (fileExists) this.setState(() => fileContent = JSON.decode(jsonFile.readAsStringSync()));
    });
  }
​
  @override
  void dispose() {
    keyInputController.dispose();
    valueInputController.dispose();
    super.dispose();
  }
​
  void createFile(Map<String, String> content, Directory dir, String fileName) {
    print("Creating file!");
    File file = new File(dir.path + "/" + fileName);
    file.createSync();
    fileExists = true;
    file.writeAsStringSync(JSON.encode(content));
  }
​
  void writeToFile(String key, String value) {
    print("Writing to file!");
    Map<String, String> content = {key: value};
    if (fileExists) {
      print("File exists");
      Map<String, String> jsonFileContent = json.decode(jsonFile.readAsStringSync());
      jsonFileContent.addAll(content);
      jsonFile.writeAsStringSync(JSON.encode(jsonFileContent));
    } else {
      print("File does not exist!");
      createFile(content, dir, fileName);
    }
    this.setState(() => fileContent = JSON.decode(jsonFile.readAsStringSync()));
    print(fileContent);
  }
​
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(title: new Text("JSON Tutorial"),),
      body: new Column(
        children: <Widget>[
          new Padding(padding: new EdgeInsets.only(top: 10.0)),
          new Text("File content: ", style: new TextStyle(fontWeight: FontWeight.bold),),
          new Text(fileContent.toString()),
          new Padding(padding: new EdgeInsets.only(top: 10.0)),
          new Text("Add to JSON file: "),
          new TextField(
            controller: keyInputController,
          ),
          new TextField(
            controller: valueInputController,
          ),
          new Padding(padding: new EdgeInsets.only(top: 20.0)),
          new RaisedButton(
            child: new Text("Add key, value pair"),
            onPressed: () => writeToFile(keyInputController.text, valueInputController.text),
          )
        ],
      ),
    );
  }
}

pubspec.yaml
name: tutorial
description: A new Flutter project.
​
dependencies:
  flutter:
    sdk: flutter
  path_provider: "^0.4.0"
​
  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.0
​
dev_dependencies:
  flutter_test:
    sdk: flutter
​
​
# For information on the generic Dart part of this file, see the
# following page: https://www.dartlang.org/tools/pub/pubspec
​
# The following section is specific to Flutter.
flutter:
​
  # The following line ensures that the Material Icons font is
  # included with your application, so that you can use the icons in
  # the material Icons class.
  uses-material-design: true
​
  # To add assets to your application, add an assets section, like this:
  # assets:
  #  - images/a_dot_burr.jpeg
  #  - images/a_dot_ham.jpeg
​
  # An image asset can refer to one or more resolution-specific "variants", see
  # https://flutter.io/assets-and-images/#resolution-aware.
​
  # For details regarding adding assets from package dependencies, see
  # https://flutter.io/assets-and-images/#from-packages
​
  # To add custom fonts to your application, add a fonts section here,
  # in this "flutter" section. Each entry in this list should have a
  # "family" key with the font family name, and a "fonts" key with a
  # list giving the asset and other descriptors for the font. For
  # example:
  # fonts:
  #   - family: Schyler
  #     fonts:
  #       - asset: fonts/Schyler-Regular.ttf
  #       - asset: fonts/Schyler-Italic.ttf
  #         style: italic
  #   - family: Trajan Pro
  #     fonts:
  #       - asset: fonts/TrajanPro.ttf
  #       - asset: fonts/TrajanPro_Bold.ttf
  #         weight: 700
  #
  # For details regarding fonts from package dependencies, 
  # see https://flutter.io/custom-fonts/#from-packages