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riverpod infinite scroll

Riverpod Infinite Scroll #
Hi! This package is a plugin for infinite_scroll_pagination that is designed to work with Riverpod.

Easy
Custom

Getting started: #
flutter pub get riverpod_infinite_scroll
flutter pub get infinite_scroll_pagination

import 'package:infinite_scroll_pagination/infinite_scroll_pagination.dart';
import 'package:riverpod_infinite_scroll/riverpod_infinite_scroll.dart';
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How it works #
This package exports a widget, RiverPagedBuilder which builds your infinite, scrollable list.
RiverPagedBuilder expects a Riverpod StateNotifierProvider
This StateNotifierProvider must implement two methods to ensure everything works correctly, it must have a load method, and a nextPageKeyBuilder method, these will be explained below.
riverpod_infinite_scroll ensures our StateNotifier will respect these constraints with the choice of two classes:
You can either use the simple:

PagedNotifier - You can create a class that extends PagedNotifier a notifier that has all the properties that riverpod_infinite_scroll needs and is intended for simple states only containing a list of records

Or if you need more flexbility to handle a more complex state object you can use a StateNotifier that uses PagedState (or a state that extends PagedState) - in such case a mixin that ensures your StateNotifier will implement the load method with the correct types is provided with PagedNotifierMixin

Example - Simple version #
Let's see an example now! We have an API that returns a list of Post objects, this API is paginated and we need to show a feed displaying those Posts.
The widget we will use for displaying such a feed is RiverPagedBuilder!. Refer to source code: easy_example.dart
class EasyExample extends StatelessWidget {

const EasyExample({Key? key} :super(key: key);

@override
Widget build(BuildContext context){
return Scaffold(
appBar: AppBar(),
body: RiverPagedBuilder<int, Post>(
firstPageKey: 0,
provider: easyExampleProvider,
itemBuilder: (context, item, index) => ListTile(
leading: Image.network(item.image),
title: Text(item.title),
),
pagedBuilder: (controller, builder) =>
PagedListView(pagingController: controller, builderDelegate: builder),
),
);
}
}
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As we can see RiverPagedBuilder is small and easy to implement with the following properties:

firstPageKey - the first page we sent to our paginated API
provider - The StateNotifierProvider that holds the logic and the list of Posts
itemBuilder - a function that builds a single Post
pagedBuilder - The type of list we want to render. This can be any of the infinite_scroll_pagination widgets, and this package already gives us the PaginationController and the BuilderDelegate

Let's see how our StateNotifier works.
Here is our model Post:
class Post {
final int id;
final String title;
final String image;
const Post({ required this.id, required this.title, required this.image });
}
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And the StateNotifier. Source code: easy_example_provider.dart
class EasyExampleNotifier extends PagedNotifier<int, Post> {

EasyExampleNotifier():
super(
//load is a required method of PagedNotifier
load: (page, limit) => Future.delayed(const Duration(seconds: 2), () {
// This simulates a network call to an api that returns paginated posts
return [
const Post(id: 1, title: "My first work", image: "https://www.mywebsite.com/image1"),
const Post(id: 2, title: "My second work", image: "https://www.mywebsite.com/image2"),
const Post(id: 3, title: "My third work", image: "https://www.mywebsite.com/image3"),
];
}),

//nextPageKeyBuilder is a required method of PagedNotifier
nextPageKeyBuilder: NextPageKeyBuilderDefault.mysqlPagination,
);

// Example of custom methods you are free to implement in StateNotifier
void add(Post post) {
state = state.copyWith(records: [ ...(state.records ?? []), post ]);
}
void delete(Post post) {
state = state.copyWith(records: [ ...(state.records ?? []) ]..remove(post));
}
}

//create a global provider as you would normally in riverpod:
final easyExampleProvider = StateNotifierProvider<EasyExampleNotifier, PagedState<int, Post>>((_) => EasyExampleNotifier());
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We can extend PagedNotifier which is a child of StateNotifier and everything will be done for us.
PagedNotifier only asks for a load function, and a nextPageKeyBuilder function that returns the next page. and that's it!
In the example above we used NextPageKeyBuilderDefault.mysqlPagination , a default function to reduce boilerplate.
NextPageKeyBuilder<int, dynamic> mysqlPagination =
(List<dynamic>? lastItems, int page, int limit) {
return (lastItems == null || lastItems.length < limit) ? null : (page + 1);
};
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Also notice the records member of the internal state object of PagedNotifier is accessible and modifiable in the standard Riverpod way through this custom function add
void add(Post post) {
state = state.copyWith(records: [ ...(state.records ?? []), post ]);
}
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A more custom example #
If you need to keep track of a more complex state than a simple list of records Riverpod Infinite Scroll also provides a more customizable approach.
Let's suppose we need to fetch from a paginated API that return a list of users. Source code: (custom_example.dart)[https://github.com/ftognetto/riverpod_infinite_scroll/blob/main/example/lib/custom/custom_example.dart]
class CustomExample extends StatelessWidget {
const CustomExample({Key? key}) : super(key: key);

@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(),
body: RiverPagedBuilder<String, User>(
firstPageKey: 'FirstPage',
provider: customExampleProvider,
itemBuilder: (context, item, index) => ListTile(
leading: Image.network(item.profilePicture),
title: Text(item.name),
),
pagedBuilder: (controller, builder) => PagedGridView(
pagingController: controller,
builderDelegate: builder,
gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
crossAxisCount: 3,
),
),
),
);
}
}
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We have used a PagedGridView here instead of a PagedListView only to make things more fun. This package works with any of the infinite_scroll_pagination widgets.

Now let's have a look of how we can create a more custom StateNotifier, first a simple class to represent a User:
class User {
final String id;
final String name;
final String profilePicture;
const User({ required this.id, required this.name, required this.profilePicture });
}
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And we have the StateNotifier that manages those users. Source code: (custom_example_provider.dart)[https://github.com/ftognetto/riverpod_infinite_scroll/blob/main/example/lib/custom/custom_example_provider.dart]
class CustomExampleNotifier extends StateNotifier<CustomExampleState>
with PagedNotifierMixin<String, User, CustomExampleState> {
CustomExampleNotifier() : super(const CustomExampleState());

@override
Future<List<User>?> load(String page, int limit) async {
try {
//as build can be called many times, ensure
//we only hit our page API once per page
if (state.previousPageKeys.contains(page)) {
await Future.delayed(const Duration(seconds: 0), () {
state = state.copyWith();
});
return state.records;
}
var users = await Future.delayed(const Duration(seconds: 3), () {
// This simulates a network call to an api that returns paginated users
return [
const User(
id: "abcdef",
name: "John",
profilePicture: "https://www.mywebsite.com/images/1"),
const User(
id: "asdfgh",
name: "Mary",
profilePicture: "https://www.mywebsite.com/images/2"),
const User(
id: "qwerty",
name: "Robert",
profilePicture: "https://www.mywebsite.com/images/3")
];
});

// we then update state accordingly
state = state.copyWith(records: [
...(state.records ?? []),
...users
], nextPageKey: users.length < limit ? null : users[users.length - 1].id,
previousPageKeys: {...state.previousPageKeys, page}.toList());
} catch (e) {
// in case of error we should notifiy the listeners
state = state.copyWith(error: e.toString());
}
}

// Super simple example of custom methods of the StateNotifier
void add(User user) {
state = state.copyWith(records: [...(state.records ?? []), user]);
}

void delete(User user) {
state = state.copyWith(records: [...(state.records ?? [])]..remove(user));
}
}

final customExampleProvider =
StateNotifierProvider<CustomExampleNotifier, CustomExampleState>(
(_) => CustomExampleNotifier());

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We didn't use PagedNotifier, instead we used a normal Riverpod StateNotifier with the PagedNotifierMixin which ensures the notifier has a correctly typed load method.
Let's take a closer look at :
Future<List<User>?> load(String page, int limit) async {
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Where does this String page get set? Well some of you may have noticed this firstPageKey whatever string is in there will be passed to the page argument of load:
body: RiverPagedBuilder<String, User>(
firstPageKey: 'FirstPage',
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It is also important to note that you are responsible for maintaining the records list:
state = state.copyWith(records: [
...(state.records ?? []),
...users
], nextPageKey: users.length < limit ? null : users[users.length - 1].id,
previousPageKeys: {...state.previousPageKeys, page}.toList());
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Also, in this example, we have used a custom state that extends PagedState, because we need another custom parameter filterByCity:
class CustomExampleState extends PagedState<String, User> {
// We can extends [PagedState] to add custom parameters to our state
final bool filterByCity;

const CustomExampleState({
this.filterByCity = false,
List<User>? records,
String? error,
String? nextPageKey,
List<String>? previousPageKeys }):
super(records: records, error: error, nextPageKey: nextPageKey);

// We can customize our .copyWith for example
@override
CustomExampleState copyWith({
bool? filterByCity,
List<User>? records,
dynamic error,
dynamic nextPageKey,
List<String>? previousPageKeys
}){
final sup = super.copyWith(
records: records,
error: error,
nextPageKey: nextPageKey,
previousPageKeys: sup.previousPageKeys);
);

return CustomExampleState(
filterByCity: filterByCity ?? this.filterByCity,
records: sup.records,
error: sup.error,
nextPageKey: sup.nextPageKey,
previousPageKeys: sup.previousPageKeys);
);
}
}
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Your custom arg for firstPageKey does not have to be a String it can be any type as specified when you declared your Notifier:
class CustomExampleNotifier extends StateNotifier<CustomExampleState>
with PagedNotifierMixin<String, User, CustomExampleState> {
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You could for example pass an Enum:
class CustomExampleNotifier extends StateNotifier<CustomExampleState>
with PagedNotifierMixin<MyEnumType, User, CustomExampleState> {
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and then just change the Generics of load and RiverPagedBuilder and your state object that extends PagedState to match.
Custom wrapper for loading/error/try again states #
The RiverPagedBuilder offers, other than the properties we already saw, the same properties that infinite_scroll_pagination offers.

firstPageProgressIndicatorBuilder - a builder for the loading state in the first call
newPageProgressIndicatorBuilder - a builder for the loading state for the subsequent requests
firstPageErrorIndicatorBuilder - a builder for the error state in the first call
newPageErrorIndicatorBuilder - a builder for the error state for the subsequent requests
noItemsFoundIndicatorBuilder - a builder for the empty state in the first call
noMoreItemsIndicatorBuilder - a builder for the empty state for the subsequent request (we have fetched all the items!)

If we need to give a coherent design to our app we could wrap the RiverPagedBuilder into a new Widget!
Testing #
An integration test is provided demonstrating how easy it is to test this widget:
https://github.com/ftognetto/riverpod_infinite_scroll/blob/main/example/integration_test/app_test.dart