---
title: Resources
description: Introduction to Resources
---

# Resources

`Resources` are special `Signal`s designed specifically to handle Async loading. Their purpose is wrap async values in a way that makes them easy to interact with handling the common states of a future __data__, __error__ and __loading__.

Resources can be driven by a `source` signal that provides the query to an async data `fetcher` function that returns a `Future`.

The contents of the `fetcher` function can be anything. You can hit typical REST endpoints or GraphQL or anything that generates a future. Resources are not opinionated on the means of loading the data, only that they are driven by futures.

Let's create a Resource:

```dart
// Using http as a client
import 'package:http/http.dart' as http;

// The source
final userId = Signal(1);

// The fetcher
Future<String> fetchUser() async {
    final response = await http.get(
      Uri.parse('https://swapi.dev/api/people/${userId.value}/'),
    );
    return response.body;
}

// The resource (source is optional)
final user = Resource(fetchUser, source: userId);
```

A Resource can also be driven from a [stream] instead of a Future.
In this case you just need to pass the `stream` field to the `Resource` class.

The resource has a value named `ResourceState`, that provides many useful convenience methods to correctly handle the state of the resource.

The `on` method forces you to handle all the states of a Resource (_ready_, _error_ and _loading_).
The are also other convenience methods to handle only specific states:
- `on` forces you to handle all the states of a Resource
- `maybeOn` lets you decide which states to handle and provide an `orElse` action for unhandled states
- `map` equal to `on` but gives access to the `ResourceState` data class
- `maybeMap` equal to `maybeOn` but gives access to the `ResourceState` data class
- `isReady` indicates if the `Resource` is in the ready state
- `isLoading` indicates if the `Resource` is in the loading state
- `hasError` indicates if the `Resource` is in the error state
- `asReady` upcast `ResourceState` into a `ResourceReady`, or return null if the `ResourceState` is in loading/error state
- `asError` upcast `ResourceState` into a `ResourceError`, or return null if the `ResourceState` is in loading/ready state
- `value` attempts to synchronously get the value of `ResourceReady`
- `error` attempts to synchronously get the error of `ResourceError`

A `Resource` provides the `fetch` and `refresh` methods.

The `refresh` method forces an update and calls the `fetcher` function again or subscribes again to the `stream`.