I am trying to save the notification title and body using shared preference but i am unable to

Question

#I am trying to save the notification title and body locally and fetch the title and body inside my app to show all the sent notification in a listview but i am unable to

#this is the code i am running this code in my main.dart inside initstate and that detail.add is my list which i created manually but i am getting error saying 102:45: Error: This expression has type 'void' and can't be used.prefs.setString('notificationData', setData); when i try to setString this is the error i get

List<String?> detail = [];
FirebaseMessaging.onMessage.listen((message) async{
      if(message.notification!=null){
        // print(message.notification!.body);
        // print(message.notification!.title);
        final title = message.notification?.title;
        final body = message.notification?.body;
         SharedPreferences prefs = await SharedPreferences.getInstance();
         final String notificationData = json.encode({"title":title,"body":body});
         final setData =  detail.add(notificationData);
        prefs.setString('notificationData', setData);
        print(notificationData);
        print(setData);
      }

Answer 1

The detail.add(notificationData) function returns nothing (void) and only adds to the existing array, so your setData variable is empty but you can use the original updated detail array like so:

FirebaseMessaging.onMessage.listen((message) async{
  if(message.notification!=null){
    // print(message.notification!.body);
    // print(message.notification!.title);
    final title = message.notification?.title;
    final body = message.notification?.body;
    SharedPreferences prefs = await SharedPreferences.getInstance();
    final String notificationData = json.encode({"title":title,"body":body});
    detail.add(notificationData);
    prefs.setString('notificationData', detail.toString());
    print(notificationData);
    print(detail);
  }
//...
});