Resource

Resources are special Signals 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.

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

Let’s create a Resource:

// 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, and can be created with Resource.stream(() => stream).

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.