binder

A lightweight, yet powerful way to bind your application state with your business logic.

The vision

As other state management pattern, binder aims to separate the application state from the business logic that updates it:

We can see the whole application state as the agglomeration of a multitude of tiny states. Each state being independent from each other. A view can be interested in some particular states and has to use a logic component to update them.

• Getting started
• Basic usage
• Intermediate usage
  • Select
  • Consumer
  • LogicLoader
  • Overrides
  • Mocking values in tests
• Advanced usage
  • Computed
  • Observers
  • Undo/Redo
  • Disposable
  • StateListener
• Snippets

Getting started

Installation

In the

pubspec.yaml

dependencies:
  binder: 

In your library add the following import:

import 'package:binder/binder.dart';

Basic usage

Any state has to be declared through a

StateRef

final counterRef = StateRef(0);

Note: A state should be immutable, so that the only way to update it, is through methods provided by this package.

Any logic component has to be declared through a

LogicRef

final counterViewLogicRef = LogicRef((scope) => CounterViewLogic(scope));

The

scope

Note: You can declare

StateRef

LogicRef

If we want our

CounterViewLogic

/// A business logic component can apply the [Logic] mixin to have access to
/// useful methods, such as `write` and `read`.
class CounterViewLogic with Logic {
  const CounterViewLogic(this.scope);

  /// This is the object which is able to interact with other components.
  @override
  final Scope scope;
  /// We can use the [write] method to mutate the state referenced by a
  /// [StateRef] and [read] to obtain its current state.
  void increment() => write(counterRef, read(counterRef) + 1);
}

In order to bind all of this together in a Flutter app, we have to use a dedicated widget called

BinderScope

MaterialApp

BinderScope(
  child: MaterialApp(
    home: CounterView(),
  ),
);

In any widget under the

BinderScope

BuildContext

class CounterView extends StatelessWidget {
  const CounterView({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    /// We call the [watch] extension method on a [StateRef] to rebuild the
    /// widget when the underlaying state changes.
    final counter = context.watch(counterRef);
return Scaffold(
  appBar: AppBar(title: const Text('Binder example')),
  body: Center(
    child: Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <widget>[
        const Text('You have pushed the button this many times:'),
        Text('$counter', style: Theme.of(context).textTheme.headline4),
      ],
    ),
  ),
  floatingActionButton: FloatingActionButton(
    /// We call the [use] extension method to get a business logic component
    /// and call the appropriate method.
    onPressed: () =&gt; context.use(counterViewLogicRef).increment(),
    tooltip: 'Increment',
    child: const Icon(Icons.add),
  ),
);
  }
}

This is all you need to know for a basic usage.

Note: The whole code for the above snippets is available in the example file.

Intermediate usage

Select

A state can be of a simple type as an

int

String

class User {
  const User(this.firstName, this.lastName, this.score);

  final String firstName;
  final String lastName;
  final int score;
}

Some views of an application are only interested in some parts of the global state. In these cases, it can be more efficient to select only the part of the state that is useful for these views.

For example, if we have an app bar title which is only responsible for displaying the full name of a

User

select

StateRef

class AppBarTitle extends StatelessWidget {
  const AppBarTitle({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final fullName = context.watch(
      userRef.select((user) => '${user.firstName} ${user.lastName}'),
    );
    return Text(fullName);
  }
}

Consumer

If you want to rebuild only a part of your widget tree and don't want to create a new widget, you can use the

Consumer

StateRef

StateRef

class MyAppBar extends StatelessWidget {
  const MyAppBar({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return AppBar(
      title: Consumer(
        watchable:
            userRef.select((user) => '${user.firstName} ${user.lastName}'),
        builder: (context, String fullName, child) => Text(fullName),
      ),
    );
  }
}

LogicLoader

If you want to trigger an asynchronous data load of a logic, from the widget side,

LogicLoader

To use it, you have to implement the

Loadable

load

final usersRef = StateRef(const []);
final loadingRef = StateRef(false);

final usersLogicRef = LogicRef((scope) => UsersLogic(scope));
class UsersLogic with Logic implements Loadable {
  const UsersLogic(this.scope);
  @override
  final Scope scope;
  UsersRepository get _usersRepository => use(usersRepositoryRef);
  @override
  Future load() async {
    write(loadingRef, true);
    final users = await _usersRepository.fetchAll();
    write(usersRef, users);
    write(loadingRef, false);
  }
}

From the widget side, you'll have to use the

LogicLoader

class Home extends StatelessWidget {
  const Home({
    Key key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return LogicLoader(
      refs: [usersLogicRef],
      child: const UsersView(),
    );
  }
}

You can watch the state in a subtree to display a progress indicator when the data is fetching:

class UsersView extends StatelessWidget {
  const UsersView({
    Key key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final loading = context.watch(loadingRef);
    if (loading) {
      return const CircularProgressIndicator();
    }
// Display the users in a list when have been fetched.
final users = context.watch(usersRef);
return ListView(...);
  }
}

Alternatively, you can use the

builder

class Home extends StatelessWidget {
  const Home({
    Key key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return LogicLoader(
      refs: [usersLogicRef],
      builder: (context, loading, child) {
        if (loading) {
          return const CircularProgressIndicator();
        }
    // Display the users in a list when have been fetched.
    final users = context.watch(usersRef);
    return ListView();
  },
);
  }
}

Overrides

It can be useful to be able to override the initial state of

StateRef

LogicRef

Reusing a reference under a different scope.

Let's say we want to create an app where a user can create counters and see the sum of all counters:

We could do this by having a global state being a list of integers, and a business logic component for adding counters and increment them:

final countersRef = StateRef(const []);

final countersLogic = LogicRef((scope) => CountersLogic(scope));
class CountersLogic with Logic {
  const CountersLogic(this.scope);
  @override
  final Scope scope;
  void addCounter() {
    write(countersRef, read(countersRef).toList()..add(0));
  }
  void increment(int index) {
    final counters = read(countersRef).toList();
    counters[index]++;
    write(countersRef, counters);
  }
}

We can then use the

select

final sum = context.watch(countersRef.select(
  (counters) => counters.fold(0, (a, b) => a + b),
));

Now, for creating the counter view, we can have an

index

index

const

A better approach would be to create a

BinderScope

BinderScope

StateRef

Any

StateRef

LogicRef

BinderScope

BinderScope

BinderScope

final indexRef = StateRef(0);

class HomeView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final countersCount =
        context.watch(countersRef.select((counters) => counters.length));
return Scaffold(
 ...
  child: GridView(
    ...
    children: [
      for (int i = 0; i < countersCount; i++)
        BinderScope(
          overrides: [indexRef.overrideWith(i)],
          child: const CounterView(),
        ),
    ],
  ),
 ...
);
  }
}

The

BinderScope

overrides

overrideWith

StateRef

LogicRef

Note: The whole code for the above snippets is available in the example file.

Mocking values in tests

Let's say you have an api client in your app:

final apiClientRef = LogicRef((scope) => ApiClient());

If you want to provide a mock instead, while testing, you can do:

testWidgets('Test your view by mocking the api client', (tester) async {
  final mockApiClient = MockApiClient();

  // Build our app and trigger a frame.
  await tester.pumpWidget(
    BinderScope(
      overrides: [apiClientRef.overrideWith((scope) => mockApiClient)],
      child: const MyApp(),
    ),
  );
  expect(...);
});

Whenever the

apiClientRef

MockApiClient

Advanced usage

Computed

You may encounter a situation where different widgets are interested in a derived state which is computed from different sates. In this situation it can be helpful to have a way to define this derived state globally, so that you don't have to copy/paste this logic across your widgets. Binder comes with a

Computed

Let's say you have a list of products referenced by

productsRef

minPriceRef

maxPriceRef

You could then define the following

Computed

return products .where((p) => p.price >= minPrice && p.price <= maxPrice) .toList(); }); ```

Like

StateRef

Computed

@override
Widget build(BuildContext context) {
  final filteredProducts = context.watch(filteredProductsRef);
  ...
  // Do something with `filteredProducts`.
}

Note: The whole code for the above snippets is available in the example file.

Observers

You may want to observe when the state changed and do some action accordingly (for example, logging state changes). To do so, you'll need to implement the

StateObserver

DelegatingStateObserver

observers

BinderScope

bool onStateUpdated(StateRef ref, T oldState, T newState, Object action) {
  logs.add(
    '[${ref.key.name}#$action] changed from $oldState to $newState',
  );

  // Indicates whether this observer handled the changes.
  // If true, then other observers are not called.
  return true;
}
...
BinderScope(
  observers: [DelegatingStateObserver(onStateUpdated)],
  child: const SubTree(),
);

Undo/Redo

Binder comes with a built-in way to move in the timeline of the state changes. To be able to undo/redo a state change, you must add a

MementoScope

MementoScope

return MementoScope(
  child: Builder(builder: (context) {
    return MaterialApp(
      home: const MyHomePage(),
    );
  }),
);

Then, in a business logic, stored below the

MementoScope

undo

redo

Note: You will get an AssertionError at runtime if you don't provide a

MementoScope

undo

redo

Disposable

In some situation, you'll want to do some action before the

BinderScope

Disposable

class MyLogic with Logic implements Disposable {
  void dispose(){
    // Do some stuff before this logic go away.
  }
}

StateListener

If you want to navigate to another screen or show a dialog when a state change, you can use the

StateListener

For example, in an authentication view, you may want to show an alert dialog when the authentication failed. To do it, in the logic component you could set a state indicating whether the authentication succeeded or not, and have a

StateListener

return StateListener(
  watchable: authenticationResultRef,
  onStateChanged: (context, AuthenticationResult state) {
    if (state is AuthenticationFailure) {
      showDialog(
        context: context,
        builder: (context) {
          return AlertDialog(
            title: const Text('Error'),
            content: const Text('Authentication failed'),
            actions: [
              TextButton(
                onPressed: () => Navigator.of(context).pop(),
                child: const Text('Ok'),
              ),
            ],
          );
        },
      );
    } else {
      Navigator.of(context).pushReplacementNamed(route_names.home);
    }
  },
  child: child,
);

In the above snippet, each time the state referenced by

authenticationResultRef

onStateChanged

DartDev Tools

Binder wants to simplify the debugging of your app. By using the DartDev tools, you will be able to inspect the current states hosted by any

BinderScope

Snippets

You can find code snippets for vscode at snippets.

Sponsoring

I'm working on my packages on my free-time, but I don't have as much time as I would. If this package or any other package I created is helping you, please consider to sponsor me so that I can take time to read the issues, fix bugs, merge pull requests and add features to these packages.

Contributions

Feel free to contribute to this project.

If you find a bug or want a feature, but don't know how to fix/implement it, please fill an issue.
If you fixed a bug or implemented a feature, please send a pull request.