Favourite Button in Flutter got unFavourited on Relaunch app - flutter

Question

I have a ListView Item with Favourite icon and I want to add functionality so that I can add list into favourite list. data is successfully added to favourite list.
Here is HomePage
body: ListView.builder(
itemCount: 100,
cacheExtent: 20.0,
padding: const EdgeInsets.symmetric(vertical: 16),
itemBuilder: (context, index) => ItemTile(index),
),
and My ListTile class I used
var favoritesList = Provider.of<Favorites>(context);
child: ListTile(
leading: CircleAvatar(
backgroundColor: Colors.primaries[index % Colors.primaries.length],
),
title: Text(
'Item $index',
key: Key('text_$index'),
),
trailing: IconButton(
key: Key('icon_$index'),
icon: favoritesList.items.contains(index)
? Icon(Icons.favorite, color: Colors.redAccent)
: Icon(Icons.favorite_border),
onPressed: () {
!favoritesList.items.contains(index)
? favoritesList.add(index)
: favoritesList.remove(index);
Scaffold.of(context).showSnackBar(
SnackBar(
content: Text(favoritesList.items.contains(index)
? 'Added to favorites.'
: 'Removed from favorites.'),
duration: Duration(seconds: 1),
),
);
},
),
),
I have a model class favourites.dart
class Favorites extends ChangeNotifier {
final List<int> _favoriteItems = [];
List<int> get items => _favoriteItems;
void add(int itemNo) {
_favoriteItems.add(itemNo);
notifyListeners();
}
void remove(int itemNo) {
_favoriteItems.remove(itemNo);
notifyListeners();
}
}
and in my favouritePage. I am getting everything perfect and also can remove favourited item but when I reopen my app I did not get any favourited item.
here is my page FavouritePage.
body: Consumer<Favorites>(
builder: (context, value, child) => ListView.builder(
itemCount: value.items.length,
padding: const EdgeInsets.symmetric(vertical: 16),
itemBuilder: (context, index) => FavoriteItemTile(value.items[index]),
),
),
FavouriteItemTile
child: ListTile(
leading: CircleAvatar(
backgroundColor: Colors.primaries[itemNo % Colors.primaries.length],
),
title: Text(
'Item $itemNo',
key: Key('favorites_text_$itemNo'),
),
trailing: IconButton(
key: Key('remove_icon_$itemNo'),
icon: Icon(Icons.close),
onPressed: () {
Provider.of<Favorites>(context, listen: false).remove(itemNo);
Scaffold.of(context).showSnackBar(
SnackBar(
content: Text('Removed from favorites.'),
duration: Duration(seconds: 1),
),
);
},
),
),
please provide the solution and can I use shared preferences with provider.

Answer 1

Yes. You should be using SharedPreferences. Add the preference library and these pieces of code
Object.dart
class Object1{
bool isLiked;
String name;
const Object1(this.name,this.isLiked);//Whatever fields you need
factory User.fromJson(Map<String, dynamic> parsedJson) {
return new Object1(
name: parsedJson['name'] ?? "",
isLiked: parsedJson['isLiked'] ?? "");
}
Map<String, dynamic> toJson() {
return {
"name": this.name,
"isLiked": this.isLiked
};
}
}
Main.dart
void main(){
setData();
runApp(MyApp);
}
void setData() async{
SharedPreferences prefs = await SharedPreferences.getInstance();
List dataList = [Object1("Name",false).toJson()];//Your items in this format
if prefs.getStringList("lists") == null:
Map decode_options = jsonDecode(dataList);
prefs.setStringList(jsonEncode(Object1.fromJson(decode_options)));
}
Now instead of a custom class for favourites, we will get all the data where we can filter. To retrieve the data afterwards, use this code
SharedPreferences prefs = await SharedPreferences.getInstance();
Map objectMap = jsonDecode(await shared_User.getStringList('list'));
List itemList = [];
for (item in objectMap):
itemList.append(User.fromJson(item));
Now you can use this Item list with the properties and the isLiked feature which is a boolean to check whether it is showed or not.
This may seem complicated but is perfectly simple though your work would be much easier if you used a database like firebase and stored these as documents

Answer 2

One option can be that you can store according to index value in shared preference and query that index value in order to see whether it is added as favourite or not. However it won't be efficient as the number of favourites increases, though still an option.

Answer 3

If you want to store on device us File(pathToFile).write(dataAsString)
You might want to save the data as json using jsonEncode(listOfNumbers) and decode using jsonDecode()
Explanation:
To save data, convert it to json and save to File on device
// NOTE: dataAsMap should be instance of class Map which stores the data you want to save
Directory localDirectory = await getApplicationDocumentsDirectory();
File(localDirectory.path + “/“ + “fileName.json”).writeAsStringSync(jsonEncode(dataAsMap));
To get data:
Map jsonData = jsonDecode(File(localDirectory.path + “/“ + “fileName.json”).readAsStringSync())