Flutter Shared Preferences acces in other class - flutter

Question

In the following class I have created a ListView of Strings which are stored sing shared preferences. Now I need to access the content of List<String> categoryList in another class. I do not know where to implement a get function to give other classes access to this List.
One Idea was to create a class for the List (But I dont want to mess up everything)
That is my Class with the List View
import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
class Categories extends StatefulWidget {
#override
_CategoriesState createState() => _CategoriesState();
}
class _CategoriesState extends State<Categories> {
List<String> categoryList = List<String>();
TextEditingController _textFieldController = TextEditingController();
#override
Widget build(BuildContext context) {
_update();
return Scaffold(
appBar: AppBar(
title: Text("Categories"),
),
body: SafeArea(
child: Container(
color: Colors.white,
child: getCategoriesListView(),
),
),
floatingActionButton: FloatingActionButton(
child: Icon(Icons.add),
onPressed: () {
setState(() {
_displayDialog(context);
});
},
),
);
}
ListView getCategoriesListView() {
return ListView.builder(
itemCount: categoryList.length,
itemBuilder: (context, int position) {
return Card(
color: Colors.white,
elevation: 2.0,
child: ListTile(
title: Text(categoryList[position]),
trailing: GestureDetector(
child: Icon(
Icons.delete,
color: Colors.grey,
),
onTap: () {
setState(() {
_delete(context, categoryList[position]);
});
},
),
),
);
});
}
void _add(BuildContext context, String category) async {
SharedPreferences prefs = await SharedPreferences.getInstance();
categoryList.add(category);
prefs.setStringList('Categories', categoryList);
}
void _delete(BuildContext context, String category) async {
SharedPreferences prefs = await SharedPreferences.getInstance();
categoryList.remove(category);
prefs.setStringList('Categories', categoryList);
}
void _update() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
setState(() {
categoryList = prefs.getStringList('Categories');
});
}
void showSnackBar(BuildContext context, String message) async {
final snackBar = SnackBar(content: Text(message));
Scaffold.of(context).showSnackBar((snackBar));
}
_displayDialog(BuildContext context) async {
_textFieldController.clear();
return showDialog(
context: context,
builder: (context) {
return AlertDialog(
title: Text('Add new category'),
content: TextField(
controller: _textFieldController,
),
actions: <Widget>[
FlatButton(
child: Text('ADD'),
onPressed: () {
setState(() {
String name = _textFieldController.text;
_add(context, name);
Navigator.of(context).pop();
});
},
),
FlatButton(
child: Text('CANCEL'),
onPressed: () {
Navigator.of(context).pop();
},
),
],
);
});
}
}
Second Class
import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
class MonthlyOverview extends StatefulWidget {
#override
_MonthlyOverviewState createState() => _MonthlyOverviewState();
}
class _MonthlyOverviewState extends State<MonthlyOverview> {
List<String> _categories = new List<String>();
#override
Widget build(BuildContext context) {
_getCategory().then((value) {
_categories = value;
});
print(_categories);
return Scaffold(
appBar: AppBar(),
body: Container(
color: Colors.white,
),
);
}
_getCategory() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
List<String> categoryList = prefs.getStringList('Categories');
return categoryList;
}
}
Console output
I/flutter (13417): []

Answer 1

#Frederik, have you tried implementing a get function in your second class and accessing the list? It could be something like this in your second class,
_getCategory() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
List<String> categoryList = prefs.getStringList('Categories');
return categoryList;
}
Call (depends on where you're calling it but this should give you an idea):
List<String> _categories = new List<String>();
_getCategory().then((value) {
_categories = value;
});
//Your _categories has the value now , use it here.
Full code:
void main() {
runApp(MaterialApp(
home: new MyApp(),
routes: <String, WidgetBuilder>{
"/monthlyOverview" : (BuildContext context)=> new MonthlyOverview(),
//add more routes here
}
));
}
class MyApp extends StatefulWidget {
#override
MyAppState createState() => MyAppState();
}
class MyAppState extends State<MyApp> {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Test'),
),
body: Padding(
padding: EdgeInsets.all(20.0),
child: Center(
child: FlatButton(
child: Text('Next', style: TextStyle(fontSize: 18.0, fontWeight: FontWeight.bold),),
onPressed: () async {
List<String> categoryList = ['Item 1', 'Item 2', 'Item 3'];
SharedPreferences prefs = await SharedPreferences.getInstance();
prefs.setStringList('Categories', categoryList);
Navigator.of(context).pushNamed("/monthlyOverview");
},
)
)
),
);
}
}
class MonthlyOverview extends StatefulWidget {
#override
_MonthlyOverviewState createState() => _MonthlyOverviewState();
}
class _MonthlyOverviewState extends State<MonthlyOverview> {
List<String> _categories = new List<String>();
#override
void initState() {
super.initState();
_getCategory().then((value) {
_categories = value;
setState(() {});
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(),
body: Center(
child: Container(
color: Colors.white,
child: _categories.length > 0 ? Text(_categories[0] + '\n' + _categories[1] + '\n' + _categories[2], style: TextStyle(fontSize: 18.0, fontWeight: FontWeight.bold),) : Text(''),
)
),
);
}
_getCategory() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
List<String> categoryList = prefs.getStringList('Categories');
return categoryList;
}
}
Hope this helps.