I have a method need to be first executed to get the items before construct the ListView.builder, how to keep this method always executed before the ListView?
class TestModel extends GetxController {
final items = <Item>[].obs;
void init() async {
items.value = getRemoteItems();
}
}
class TestScreen extends StatelessWidget {
final TestModel testModel = Get.put(TestModel());
#override
Widget build(BuildContext context) {
if (testModel.items.isEmpty) {
testModel.init(); // It seems the ListView can not get the testModel's items.
}
return Obx(
() => ListView.builder(
itemCount: testModel.items.length, // But the items length is always 0.
itemBuilder: (context, index) {
final item = testModel.items[index];
...
}
}
Probably, you can't do that but you can update your ui when it occurs. Can you try this?
class TestModel extends GetxController {
final items = <Item>[];
String token = ''; //if it's dynamic, don't do this...
void onInit() {
// this runs your method at the beginning
// but if you wanna aviod this,
// you can remove here.
foo();
}
void foo(
String token //...do this and run this with token.
) async {
items.value = await getRemoteItems(token);
update();
}
}
class TestScreen extends StatelessWidget {
final TestModel testModel = Get.put(TestModel());
#override
Widget build(BuildContext context) {
if (testModel.items.isEmpty) {
testModel.foo();
return Container(); // or loading screen.
}
return GetxController<TestModel>(
builder: (_) => ListView.builder(
itemCount: _.items.length,
itemBuilder: (context, index) {
final item = _.items[index];
...
}
}
Related
I'm using the Provider package for state management in a Flutter app and I have a list model extending ChangeNotifier.
In the list model there is a method to replace a certain element in the list like this:
class MyListModel extends ChangeNotifier {
List<MyListItem> _myList = [];
void replace(Data data) {
int index = _findById(data.id);
if(index == -1) {
return;
}
_myList[index] = MyListItem(data);
log("After replace: " + _myList.toString());
notifyListeners();
}
void add(MyListItem myItem) {
_myList.add(myItem);
notifyListeners();
}
void remove(MyListItem myItem) {
_myList.remove(myItem);
notifyListeners();
}
}
This is the lis and the list item class where the provider is consumed:
class _MyListView extends StatelessWidget {
final Data _data;
const _SelectUpcomingMealList(this.upcomingMeal);
#override
Widget build(BuildContext context) {
return ListView.builder(
padding: const EdgeInsets.all(16.0),
itemBuilder: (context, index) {
return MyListItem(_data);
}
);
}
}
class MyListItem extends StatelessWidget {
final Data _data;
MyListItem(this._data);
#override
Widget build(BuildContext context) {
return Consumer<MyListModel>(
builder: (context, myListModel, children) => ListTile(
title: Text(_data.name),
subtitle: Text(_data.description),
trailing: const Icon(Icons.add),
onTap: () => replaceMyItem(myListModel, context),
)
);
}
void replaceMyItem(MyListModel myListModel, BuildContext context) {
myListModel.replace(_data);
Navigator.pop(context);
}
}
For some reason the UI is not updating and the replaced item is not displayed, the old item is visible. The logging shows that the list is properly updated (the index also properly calculated), the replaced element is there, but the UI does not update.
The add() and remove() methods work, in these cases the UI properly reflects the change.
Is there something I'm missing in case of an item being replaced?
I am facing very weird problem. i am using bloc with freezed, injectable and dartz. i just need to get data from SQl database and display it when a today page opened.
The code of UI is:
class TodayPage extends HookWidget {
const TodayPage();
#override
Widget build(BuildContext context) {
return BlocProvider<ScheduledNotesCubit>(
lazy:false,
create: (context) => getIt<ScheduledNotesCubit>()
..countDoneNoteOutOfAllNotes()
..retrieveData(),
child: BlocBuilder<ScheduledNotesCubit, ScheduledNotesState>(
builder: (context, state) {
return ListView.builder(
itemCount: state.maybeMap(
orElse: () {}, getNotesCount: (g) => g.noteCount),
itemBuilder: (BuildContext context, int index) {
return Text(
"${state.maybeMap(orElse: () {}, getNotes: (notes) {
return notes.getNotes[index]['content'];
})}",
);
},
);
},
),
);
}
}
The code of state is:
#freezed
class ScheduledNotesState with _$ScheduledNotesState {
const factory ScheduledNotesState.initial() = _Initial;
const factory ScheduledNotesState.getNotes({required List<Map<String, dynamic>> getNotes}) = _GetNotes;
const factory ScheduledNotesState.getNotesCount({required int noteCount}) = _GetNotesCount;
const factory ScheduledNotesState.getCountDoneNoteOutOfAllNotes({required String getCountDoneNoteOutOfAllNotes}) = _GetCountDoneNoteOutOfAllNotes;
const factory ScheduledNotesState.updateIsDoneNote({required int updateIsDoneNote}) = _UpdateIsDoneNote;
}
The code of cubit is:
#injectable
class ScheduledNotesCubit extends Cubit<ScheduledNotesState> {
ScheduledNotesCubit(this._noteRepository)
: super(const ScheduledNotesState.initial());
final NoteRepository _noteRepository;
// retrieve data
void retrieveData() async {
return emit(ScheduledNotesState.getNotes(
getNotes: await _noteRepository.retrieveData()));
}
}
This Cubit Does not return a value in listView, instead it returns null values, But When i try to do so it works!!!!!!
the updated cubit code is:
#injectable
class ScheduledNotesCubit extends Cubit<ScheduledNotesState> {
ScheduledNotesCubit(this._noteRepository)
: super(const ScheduledNotesState.initial());
final NoteRepository _noteRepository;
// retrieve data
void retrieveData() async {
var d= await _noteRepository.retrieveData(); //-->updated
var x= d[1]['content']; //-->updated
print("\n $x \n") ; // -->updated
return emit(ScheduledNotesState.getNotes(
getNotes: await _noteRepository.retrieveData()));
}
}
Can you try add lazy to false for BlocProvider, and update this code:
void retrieveData() {
_noteRepository.retrieveData().then((value) {
emit(ScheduledNotesState.getNotes(getNotes: value));
});
}
The solution is create a data class for the cubit, instead of creating a sealed classes.
I have a Flutter widget which gets data from a server and renders a List. After getting the data, I parse the data and convert it to an internal object in my application, so the function is something like this:
Future<List<Data>> getData(Thing thing) async {
var response = await http.get(Uri.parse(MY_URL));
// do some processing
return data;
}
After that, I've defined a stateful widget which calls this function and takes the future to render a List.
class DataList extends StatefulWidget {
const DataList({Key key}) : super(key: key);
#override
_DataListState createState() => _DataListState();
}
class _DataListState extends State<DataList> {
Widget createListView(BuildContext context, AsyncSnapshot snapshot) {
List<Data> values = snapshot.data;
if (values.isEmpty) {
return NoResultsWidget('No results.');
}
return ListView.builder(
itemCount: values.length,
itemBuilder: (BuildContext context, int index) {
return values[index];
},
);
}
#override
Widget build(BuildContext context) {
var data = getSomething().then((thing) => getData(thing));
return FutureBuilder(
future: data,
builder: (BuildContext context, AsyncSnapshot snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.none:
return CustomErrorWidget('Error');
case ConnectionState.waiting:
return LoadingWidget();
default:
if (snapshot.hasError) {
return CustomErrorWidget('Error.');
} else {
return createListView(context, snapshot);
}
}
},
);
}
}
Now, the code works just fine in this manner. But, when I try to move my data to be a class variable (of type Future<List>) that I update through the initState method, the variable just never updates. Example code below:
class _DataListState extends State<DataList> {
Future<List<Data>> data;
....
#override
void initState() {
super.initState();
updateData();
}
void updateData() {
data = getSomething().then((thing) => getData(thing));
}
....
}
I want to add a refresh indicator to update the data on refresh, and to do that I need to make my data a class variable to update it on refresh, but I can't seem to figure out how to make my data part of the state of the stateful widget and have it work. any help or guides to a github code example would be appreciated.
You need to wrap the assignment of the data variable in setState so that Flutter knows the variable changed and rebuilds your widget.
For example:
void updateData() {
setState(() {
data = getSomething().then((thing) => getData(thing));
});
}
I'm using the Getx controller in my project. I have create the controller for FutureBuilder for displaying list but .Obs is not set on Future Function. I'm sharing the code.
class PPHomeController extends GetxController {
Future<List<PPProductRenterModel>> listNearProduct;
// i want to set .Obs end of the "listNearProduct" but it's not working because of Future.
FetchNearProductList({#required int price}) async {
listNearProduct = CallGetNearProducts();// Http API Result
}
}
{
PPHomeController _homeController = Get.put(PPHomeController());
Widget mainProductListView() {
return FutureBuilder<List<PPProductRenterModel>>
(builder: (context, AsyncSnapshot<List<PPProductRenterModel>> projectSnap){
if(!projectSnap.hasData){
if(projectSnap.connectionState == ConnectionState.waiting){
return Container(
child: Loading(),
);
}
}
return ListView.builder(
itemCount: projectSnap.data.length,
itemBuilder: (context, index) {
PPProductRenterModel model = projectSnap.data[index];
PPPrint(tag: "CheckId",value: model.productId);
return ProductMainItemRow(model);
});
},
future: _homeController.listNearProduct,);
There is a cleaner way for implementing List in GetX without worrying about Type-Casting:
Instantiate it:
final myList = [].obs;
Assign it:
myList.assignAll( listOfAnyType );
(Reference) Flutter error when using List.value :
'value' is deprecated and shouldn't be used. List.value is deprecated.
use [yourList.assignAll(newList)]. Try replacing the use of the
deprecated member with the replacement.
Detailed code example
ProductController.dart
class ProductController extends GetxController {
final productList = [].obs;
#override
void onInit() {
fetchProducts();
super.onInit();
}
void fetchProducts() async {
var products = await HttpServices.fetchProducts();
if (products != null) {
productList.assignAll(products);
}
}
}
HttpServices.dart
class HttpServices {
static var client = http.Client();
static Future<List<Product>> fetchProducts() async {
var url = 'https://link_to_your_api';
var response = await client.get(url);
if (response.statusCode == 200) {
return productFromJson(response.body);
} else {
return null;
}
}
}
product.dart
class Product {
Product({
this.id,
this.brand,
this.title,
this.price,
....
});
....
}
Form the docs:
3 - The third, more practical, easier and preferred approach, just add
.obs as a property of your value:
final items = <String>[].obs;
Following that instruction, this should work:
final listNearProduct = Future.value(<PPProductRenterModel>[]).obs;
E.g.:
// controller
final list = Future.value(<String>[]).obs;
#override
void onInit() {
super.onInit();
fetchList();
}
Future<List<String>> callApi() async {
await Future.delayed(Duration(seconds: 2));
return ['test'];
}
void fetchList() async {
list.value = callApi();
}
// screen
#override
Widget build(BuildContext context) {
return GetX<Controller>(
init: Controller(),
builder: (controller) {
return FutureBuilder<List<String>>(
future: controller.list.value,
builder: (context, snapshot) {
if (snapshot.hasData) {
print(snapshot.data[0]); // Output: test
return Text(snapshot.data[0]);
} else if (snapshot.hasError) {
return Text("${snapshot.error}");
}
// By default, show a loading spinner.
return CircularProgressIndicator();
},
);
},
);
};
You never actually call FetchNearProductList.
You need to call it in some place, preferably before the FutureBuilder uses that Future.
I'm brand new to Flutter / Dart and I'm trying to build a reusable infinite scroller with placeholder loading. The class is as follows:
import 'dart:async';
import 'package:flutter/material.dart';
class PagedScroller<T> extends StatefulWidget {
final int limit;
final Future<List<T>> Function(int, int) getDataFunction;
final Widget Function(T) renderFunction;
final Widget Function() renderPlaceholderFunction;
PagedScroller(
{#required this.limit,
#required this.getDataFunction,
#required this.renderFunction,
#required this.renderPlaceholderFunction});
#override
_PagedScrollerState<T> createState() => _PagedScrollerState<T>();
}
class _PagedScrollerState<T> extends State<PagedScroller> {
int _offset = 0;
int _lastDataLength = 1; // Init to one so the first call can happen
List<dynamic> _items = [];
Future<List<dynamic>> _future;
bool _isInitializing = false;
bool _isInitialized = false;
bool _isLoading = false;
ScrollController _controller =
ScrollController(initialScrollOffset: 0.0, keepScrollOffset: true);
_PagedScrollerState();
void _init() {
_isInitializing = true;
_reset();
_controller.addListener(() {
bool loadMore = false;
if (_controller.position.maxScrollExtent == double.infinity) {
loadMore = _controller.offset == _controller.position.maxScrollExtent;
} else {
loadMore =
_controller.offset >= _controller.position.maxScrollExtent * 0.85;
}
// Only load more if it's not currently loading and we're not on the last page
// _lastDataLength should be 0 if there are no more pages
if (loadMore && !_isLoading && _lastDataLength > 0) {
_offset += widget.limit;
_load();
}
});
_load();
_isInitializing = false;
_isInitialized = true;
}
void _reset() {
// Clear things array and reset inital get-things link (without paging)
setState(() {
_future = _clearThings();
});
// Reload things
// Reset to initial GET link
_offset = 0;
}
void _load() {
setState(() {
_future = _loadPlaceholders();
_future = _loadData();
});
}
Future<List<dynamic>> _clearThings() async {
_items.clear();
return Future.value(_items);
}
Future<List<dynamic>> _loadPlaceholders() async {
// Add 20 empty placeholders to represent stuff that's currently loading
for (var i = 0; i < widget.limit; i++) {
_items.add(_Placeholder());
}
return Future.value(_items);
}
List<dynamic> _getInitialPlaceholders() {
var placeholders = List<dynamic>();
for (var i = 0; i < widget.limit; i++) {
placeholders.add(_Placeholder());
}
return placeholders;
}
Future<List<dynamic>> _loadData() async {
_setLoading(true);
var data = await widget.getDataFunction(widget.limit, _offset);
// When loading data is done, remove any placeholders
_items.removeWhere((item) => item is _Placeholder);
// If 0 items were returned, it's probably the last page
_lastDataLength = data.length;
for (var item in data) {
_items.add(item);
}
_setLoading(false);
return Future.value(_items);
}
void _setLoading(bool isLoading) {
if (!mounted) {
return;
}
setState(() {
_isLoading = isLoading;
});
}
Future<void> _refreshThings() async {
_reset();
_load();
return Future;
}
#override
Widget build(BuildContext context) {
if (!_isInitializing && !_isInitialized) {
_init();
}
return FutureBuilder(
future: _future,
initialData: _getInitialPlaceholders(),
builder: (BuildContext context, AsyncSnapshot snapshot) {
if (snapshot.hasData) {
List<dynamic> loadedItems = snapshot.data;
return RefreshIndicator(
onRefresh: _refreshThings,
child: ListView.builder(
itemCount: loadedItems.length,
controller: _controller,
physics: const AlwaysScrollableScrollPhysics(),
itemBuilder: (BuildContext context, int index) {
var item = loadedItems[index];
if (item is _Placeholder) {
return widget.renderPlaceholderFunction();
} else if (item is T) {
// THIS IS THE LINE THAT FAILS
return widget.renderFunction(item);
}
return Text('Unknown item type');
},
),
);
}
return Container();
},
);
}
}
class _Placeholder {}
The line that fails above:
return widget.renderFunction(item);
Fails with the following:
type '(MyModel) => Widget' is not a subtype of type '(dynamic) => Widget'
I understand why this is happening. The compiler can't know that type T from my PagedScroller<T> is the same as type T from _PagedScrollerState<T>. As a result, Dart tries to be helpful and converts my callback function of type Widget Function(T) to Widget Function(dynamic).
I then figured "maybe I can fake it out" with the following since I know the T in PagedScroller<T> and _PagedScrollerState<T> are always the same:
var renderFunction = widget.renderFunction as Widget Function(T);
return renderFunction(item);
Interestingly, this gives me a warning:
Unnecessary cast.
Try removing the cast.
Yet it won't even run that line (crashes) with the following:
Either the assertion indicates an error in the framework itself, or we should provide substantially more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
https://github.com/flutter/flutter/issues/new?template=BUG.md
Changing everything to dynamic works a charm, but I really don't want to lose the readability of generics here if I don't have to.
Despite extensive searching, I can't find the equivalent of C#'s Convert.ChangeType where you can provide types at runtime so I can just do the cast I want and be done with it.
This seems like a really simple thing to achieve, but I'm stuck.
You can consume the scroller with this simple main.dart copy/pasted:
import 'package:flutter/material.dart';
import 'package:minimal_repros/paged_scroller.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
#override
Widget build(BuildContext context) {
Future<List<MyModel>> getDataFunction(int limit, int offset) async {
var myModels = List<MyModel>();
// Simulate API call
await Future.delayed(Duration(milliseconds: 1000));
for (int i = 0; i < limit; i++) {
var myModel = MyModel();
myModel.count = i + offset;
myModel.firstName = 'Bob';
myModels.add(myModel);
}
return myModels;
}
Widget renderFunction(MyModel myModel) {
return Text(myModel.firstName);
}
Widget renderPlaceholderFunction() {
return Text('Loading');
}
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: PagedScroller(
getDataFunction: getDataFunction,
renderFunction: renderFunction,
renderPlaceholderFunction: renderPlaceholderFunction,
limit: 20));
}
}
class MyModel {
int count;
String firstName;
}
In the declaration of your State class, you forgot to specify the generic parameter of the widget.
Instead of:
class _PagedScrollerState<T> extends State<PagedScroller> {
do:
class _PagedScrollerState<T> extends State<PagedScroller<T>> {