So Im trying to save an object(with only one String attribute) in the ObjectBox. The ObjectBox is called favoriteBox. With the onLongPress-function im trying to put the object in the box. In the initState-function im trying to put all the objects (more specific: the string attributes of each object) in to a nested list.
My problem now is that after calling the onLongPress-function and putting the object in the favoriteBox, the favoritBox is null according to the Debugger.
Im not sure where my mistake is.
class _GridViewJokesState extends State<GridViewJokes> {
late int seasonsListIndex;
List<List<String?>> seasonsList = seasons;
final toast = FToast();
final AudioPlayer audioPlayer = AudioPlayer();
late SeasonProvider seasonProvider;
Store? _store;
Box<FavoritesEntity>? favoritesBox;
#override
void initState() {
super.initState();
toast.init(context);
getApplicationDocumentsDirectory().then((dir) {
_store = Store(getObjectBoxModel(), directory: dir.path + "/objectbox");
});
favoritesBox = _store?.box<FavoritesEntity>();
seasonsList[5] =
favoritesBox?.getAll().map((e) => e.quoteName).toList() ?? [];
}
void onLongPress(listTileIndex) {
if (seasonProvider.seasonPicked) {
seasonsList[5].add(seasonsList[seasonsListIndex][listTileIndex]);
favoritesBox?.put(FavoritesEntity(
quoteName: seasonsList[seasonsListIndex][listTileIndex]));
toast.showToast(
child: buildToast("Zu Favoriten hinzugefügt"),
gravity: ToastGravity.BOTTOM);
}
import 'package:objectbox/objectbox.dart';
#Entity()
class FavoritesEntity {
FavoritesEntity({required this.quoteName});
int id = 0;
String? quoteName;
}
The issue is that the code does not await the Future that returns the application Documents directory before accessing store. So store will still be null and the following line that gets a box does nothing.
getApplicationDocumentsDirectory().then((dir) {
_store = Store(getObjectBoxModel(), directory: dir.path + "/objectbox");
});
// store is still null here:
favoritesBox = _store?.box<FavoritesEntity>();
You can either move the box get code into the then() closure. Or, as we recommend, init Store into a global variable using a helper class in the main function. See our examples.
Related
I'm very surprised after this issue. First, inform all things I have used in my project.
I have used Getx in my project. I have called the API using the Getx controller file.
Below code used in getx controller file. "PLTimeSlotModel" is model and. it has two params (name, isselect).
var futureTimeSlot_PL_C_D = Future.value(<PLTimeSlotModel>[]).obs;
callTimeSlotAPI() async {
futureTimeSlot_PL_C_D.value = FetchTimeSlotList();
}
Future<List<PLTimeSlotModel>> FetchTimeSlotList() async {
// Fetching data with API calling
}
Screen A:
List<PLTimeSlotModel> listA = [];
List<PLTimeSlotModel> listB = [];
#override
void initState() {
super.initState();
_plController.callTimeSlotAPI();
}
Another method is to create two lists using the future list:
List<PLTimeSlotModel> temp1 = await _plController.futureTimeSlot_PL_C_D.value;
temp1.forEach((element) {
listA.add(element);
listB.add(element);
});
onclick:
for(int i =0;i<listA.length;i++){
listA[i].isselect = false;
print(listA[i].isselect);
print(listB[i].isselect);
}
Now the issue is I have changed/updated the only "listA" value, So why automatically set the same value to "listB"? The two list is based on the one list.
A List in Dart contains references objects, not the objects themselves. So what you are doing is copying references to objects into two lists. But since they are pointing at the same objects, you will see any modification in one list also happen in the other list. You need to copy each PLTimeSlotModel object and put the copy into your new list.
One way to copy objects is to create an constructor which takes an object of the same type and creates a new object based on this first object. So something like this:
class Person {
String name;
Person(this.name);
Person.fromPerson(Person other) : this(other.name);
#override
String toString() => 'Person($name)';
}
void main() {
final persons = [
Person('Adam'),
Person('Bob'),
];
// Make new list based on persons
final otherPersonList = [
...persons.map((person) => Person.fromPerson(person))
];
otherPersonList[0].name = 'Carl';
print(persons); // [Person(Adam), Person(Bob)]
print(otherPersonList); // [Person(Carl), Person(Bob)]
}
I have a model called category , which has two fields, User has a list of categories and what to update the category name, for State Management getx is used
class Category {
String? categoryName;
bool status;
Category(this.categoryName,this.status);
}
I have a observable list called catList which is used in List widget
var catList = <Category>[].obs;
when I update the category field it doest not update
catList[index].categoryName = categoryChangedName.value;
but If I update the item in object and then assign the object to catList then It changed
catList[index] = Category(categoryChangedName.value, catList[index].status );
My question is how to make model fields observable, if we have more fields changes then this is not proper way.
As of GetX documentation you need to update values using method and call update(); method inside custom object !
Ex:
class Controller extends GetxController {
int counter = 0;
void increment() {
counter++;
update(); // look here!
}
}
Your use case might be like....
class Category {
String? categoryName;
bool status;
Category(this.categoryName,this.status);
void updateCategoryName(name){
this.categoryName = name;
update();
}
}
//Use like..
catList[index].updateCaetgoryName = categoryChangedName.value;
As you can see from my code sample, I'm using this variable. I also reference multiple times later in the class.
Flutter Warning - info: The value of the field '_loadTimer' isn't used. (unused_field at [app] lib/models/knowledge_level/pb_cycle_permissions_collection.dart:12)
ng is: info: The value of the field '_loadTimer' isn't used. (unused_field at [app] lib/models/knowledge_level/pb_cycle_permissions_collection.dart:12)
import 'dart:async';
import 'dart:collection';
import 'package:app/data/graphql/queries.dart';
import 'package:app/helpers/shared_logger.dart';
import 'package:flutter/cupertino.dart';
import '../command_permission.dart';
class PBCyclePermissionsCollection
with ListMixin<CommandPermission>, ChangeNotifier {
Timer? _loadTimer;
///
/// CONSTRUCTION AND INITIALIZATION
///
static final PBCyclePermissionsCollection _instance =
PBCyclePermissionsCollection._internal();
factory PBCyclePermissionsCollection() {
return _instance;
}
/// ACCESS SINGLETON VIA myPBCyclePermInstance = PBCyclePermissionsCollection()
PBCyclePermissionsCollection._internal() {
_loadTimer = Timer(_waitFirstLoad, _attemptLoad);
}
///
/// PRIVATE VARIABLES AND METHODS
///
static final Duration _waitFirstLoad = Duration(milliseconds: 500);
static final Duration _waitRetryLoad = Duration(seconds: 2);
static final int _maxAttempts = 4;
int _loadAttempts = 0;
bool _isReady = false;
bool _hasFailed = false;
/// Storage of CommandPermissions List once loaded
final List<CommandPermission> _list = [];
void _attemptLoad() async {
_loadAttempts++;
SharedLogger.I().d('_attemptLoad() current load attempt: ${_loadAttempts}');
try {
final results = await Queries.getCommandPermissions();
var data = results.data!['commandPermissions'];
var permissions = <CommandPermission>[];
for (var item in data) {
permissions.add(CommandPermission.fromJson(item));
}
/// Populated class with loaded objects.
_list.clear();
_list.addAll(permissions);
_isReady = true;
notifyListeners();
} catch (e) {
SharedLogger.I().e('Error loading PBCycle Permissions - ${e}');
_newAttempt();
}
}
void _newAttempt() {
SharedLogger.I().d(
'_newTry() _loadAttempts: ${_loadAttempts} _maxAttempts:${_maxAttempts} '
'creating new loadTimer for another try? : ${!(_loadAttempts >= _maxAttempts)}');
if (_loadAttempts >= _maxAttempts) {
_hasFailed = true;
notifyListeners();
// TODO: do we invalidate any existing data that may have been loaded before? Like if this load cycle is a refresh?
// If so, we should reset _isReady and _list;
return;
}
_loadTimer = Timer(_waitRetryLoad, _attemptLoad);
}
///
/// PUBLIC METHODS
///
bool get isLoaded {
return _isReady;
}
bool get hasFailed {
return _hasFailed;
}
#override
set length(int newLength) {
throw ('length cannot be changed externally');
}
#override
int get length {
return _list.length;
}
#override
CommandPermission operator [](int index) {
return _list[index];
}
#override
void operator []=(int index, CommandPermission value) {
throw ('Cannot modify list from outside');
}
}
Image of IDE with Code Sample and associated Dart Analysis Hints
You aren't actually using it, you're just setting the value multiple times
The answer from Andrew is correct, but a bit unclear since unsure what 'it' refers to. Here's another way to explain what the warning message means:
Notice that the message says you are not using the value. You are using the variable, but not its value. You are assigning the value. To read the value would be using it.
That said, the question is answered, but I think the question is somewhat vague by asking "what am i missing". What do you (OP) want to achieve? I assume it's to not see that warning anymore. And that is what brings me to this post. I have similar issue. I too have a class variable for a Timer and I get this same warning message. One does not need to read the value in order to use a timer but the analyzer doesn't know that. While writing this response I have discovered that you can a suppress warning. How about this:
// ignore: unused_field
Timer? _loadTimer;
Hello I want to add some value to my list. I have already googled for solutions but I can't see any other solutions besides initializing the list which I did.
When I try to add an item to my AutomaticDateList class I get the error:
The method 'add' was called on null.
Receiver: null
Tried calling: add(Instance of 'AutomaticDate')
Here is the class with the list in it.
class AutomaticDateList with ChangeNotifier {
List<AutomaticDate> items = []; // here I inialize
AutomaticDateList({this.items});
void addToList(AutomaticDate automaticDate) {
items.add(automaticDate);
notifyListeners();
}
List<AutomaticDate> get getItems => items;
}
This is the item I want to add to the list.
class AutomaticDate with ChangeNotifier {
String date;
String enterDate;
String leaveDate;
String place;
AutomaticDate({this.date, this.enterDate, this.leaveDate, this.place});
Here I call the method using the provider inside a page widget
void onGeofenceStatusChanged(Geofence geofence, GeofenceRadius geofenceRadius,
GeofenceStatus geofenceStatus) {
geofenceController.sink.add(geofence);
AutomaticDate automaticDateData = AutomaticDate();
automaticDateData.place = geofence.id;
automaticDateData.date = DateFormat("dd-mm-yyyy").format(DateTime.now());
if (geofenceStatus == GeofenceStatus.ENTER) {
widget.enterDate = DateFormat("HH:mm:ss").format(DateTime.now());
} else {
automaticDateData.leaveDate =
DateFormat("HH:mm:ss").format(DateTime.now());
automaticDateData.enterDate = widget.enterDate;
widget.list.add(automaticDateData);
WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
AutomaticDateList automaticDateList =
Provider.of<AutomaticDateList>(context, listen: false);
automaticDateList.items.add(automaticDateData); // Here I add the data and get error "add was called on null"
print(automaticDateList.getItems);
});
}
}
The problem is in the initialization:
List<AutomaticDate> items = []; // here I inialize
AutomaticDateList({this.items});
You set a default value, but you are using the "auto-assign" sintax in the constructor, saying that items passing in the parameters are going to be assigned in the items property of the class.
You are instantiating the class using this code:
AutomaticDate automaticDateData = AutomaticDate();
So, you are passing "null" implicitly as parameter, then items [] got replaced with null value.
Just change the code to:
List<AutomaticDate> item;
AutomaticDateList({this.items = []}); // Default value
I am making a pokemon app and I have a question that I already had in other projects and I would like to know if anyone can help me with a solution.
I receive a variable called pokemonName from other screen, I want to pass the variable and concatenate with the class "Strings", it will be like Strings.+pokemonName.toLowerCase(), converting to lowercase to get the map from the class Strings, but I don't know how to achieve this to remove the switch and don't need to use a lot of cases for each pokemon.
class PokemonDetailScreen extends StatelessWidget {
final String pokemonName;
final String image;
Map<String, dynamic> pokemonMap = {};
PokemonDetailScreen(this.pokemonName, this.image, this.index){
getPokemonMap();
}
#override
Widget build(BuildContext context) {
return Container();
}
void getPokemonMap(){
switch(pokemonName){
case "Bulbasaur":
pokemonMap = Strings.bulbasaur;
break;
case "Charmander":
pokemonMap = Strings.charmander;
break;
}
}
}
**Class in another dart file:**
class Strings {
static Map bulbasaur = {};
}
What I needed is something like this:
void getPokemonMap(){
pokemonMap = Strings.$pokemonMap.toLowerCase();
}
What you could do is have a static map indexed by the name of your Pokemons and whose values are maps.
class Strings {
static Map<String, dynamic> map = {
'Bulbasor': {},
'Charmander': {},
// ...
};
}
And you’ll use it like this: pokemonMap = Strings.map[pokemonName].
~You can use JSON file to do all this things instead use a class.~
I recommend not use a static class to do that thing, instead you can just make a normal class and instantiate on another file, so when the class that you call your another class will be dispose when the parent was.
class PokemonStrings {
Map bulbasaur = {your map here};
}
To call that in another file you need just do
PokemonString _pokemonString = PokemonString();
And call whatever you need in the class that you instantiate
var bulbasaurMap = _pokemonString.bulbasaur;
But even so you need walk with static class. Just call the name of class followed by dot to access all the static attributes
var bulbasaurMap = PokemonString.bulbasaur;