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A simple State Management solution for Dart applications inspired by SolidJS

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A simple state-management library inspired by SolidJS. #

The objectives of this project are:

  1. Being simple and easy to learn
  2. Fits well with the framework's good practices
  3. Do not have a single global state, but multiple states only in the most appropriate places
  4. No code generation

Learning #

For a comprehensive and updated documentation go to The Official Documentation

There are 4 main concepts you should be aware:

  1. Signals
  2. Effects
  3. Computed
  4. Resources

Signals #

Signals are the cornerstone of reactivity in solidart. They contain values that change over time; when you change a signal's value, it automatically updates anything that uses it.

To create a signal, you have to use the Signal class:

final counter = Signal(0);

The argument passed to the class is the initial value, and the return value is the signal.

To retrieve the current value, you can use:

print(counter.value); // prints 0
// or
print(counter());

To change the value, you can use:

// Increments by 1
counter.value++; 
// Set the value to 2
counter.value = 2;
// equivalent to
counter.set(2);
// Update the value based on the current value
counter.updateValue((value) => value * 2);

Effects #

Signals are trackable values, but they are only one half of the equation. To complement those are observers that can be updated by those trackable values. An effect is one such observer; it runs a side effect that depends on signals.

An effect can be created by using the Effect class. The effect automatically subscribes to any signal and reruns when any of them change. So let's create an Effect that reruns whenever counter changes:

final disposeFn = Effect((_) {
    print("The count is now ${counter.value}");
});

Computed #

A computed signal is a signal that depends on other signals. To create a computed signal, you have to use the Computed class.

A Computed automatically subscribes to any signal provided and reruns when any of them change.

final name = Signal('John');
final lastName = Signal('Doe');
final fullName = Computed(() => '${name.value} ${lastName.value}');
print(fullName()); // prints "John Doe"

// Update the name
name.set('Jane');
print(fullName()); // prints "Jane Doe"

Resources #

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.

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:

// 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
final user = Resource(fetcher: 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.

If you're using ResourceBuilder you can react to the state of the resource:

ResourceBuilder(
  resource: user,
  builder: (_, userState) {
    return userState.on(
      ready: (data) {
        return Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            ListTile(
              title: Text(data),
              subtitle:
                  Text('refreshing: ${userState.isRefreshing}'),
            ),
            userState.isRefreshing
                ? const CircularProgressIndicator()
                : ElevatedButton(
                    onPressed: user.refresh,
                    child: const Text('Refresh'),
                  ),
          ],
        );
      },
      error: (e, _) {
        return Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            Text(e.toString()),
            userState.isRefreshing
                ? const CircularProgressIndicator()
                : ElevatedButton(
                    onPressed: user.refresh,
                    child: const Text('Refresh'),
                  ),
          ],
        );
      },
      loading: () {
        return const RepaintBoundary(
          child: CircularProgressIndicator(),
        );
      },
    );
  },
)

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.

DevTools #

You can debug your application using the Solidart DevTools extension and filter your signals.

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A simple State Management solution for Dart applications inspired by SolidJS

Repository (GitHub)
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Topics

#state-management #signals

Documentation

Documentation
API reference

License

MIT (LICENSE)

Dependencies

collection, meta

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