just 1.0.18

A very lightweight state management library.

Just

Just: a lightweight state management library for Flutter. Base on Provider

Usage

1、Definition ViewModel

ViewModel is state holder, contain State and Action。

class HomeViewModel extends ViewModel {
  // state definition
  final count = 0.obs;
  final now = Obs(DateTime.now());
  final name = Obs<String?>(null);
  final age = Obs<int>(10); // 10.obs or Obs(10);

  // action1
  void increment() {
    final newValue = count.value + 1;
    // update state
    setValue(count, newValue);
  }

  // action2
  void syncTime() {
    // update state
    setValue(now, DateTime.now());
  }

  // action3
  void syncUserInfo() {
    var newAge = Random().nextInt(100);
    setValue(age, newAge);
    var wordPair = generateWordPairs().first;
    setValue(name, wordPair.asCamelCase);
  }

  @override
  void dispose() {
    // do something when dispose
    super.dispose();
  }
}

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2、Integration ViewModel

Provider viewModel by ViewModelProvider.

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    // integration viewModel (state holder)
    return ViewModelProvider(
      create: (context) => HomeViewModel(),
      child: _HomePage(),
    );
  }
}

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3、DataBinding and Action

Get ViewModel like this:

final viewModel = context.viewModel<HomeViewModel>();

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Binding data like this:

DataBinding(() => Text('count: ${viewModel.count.value}' ))

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Widget in DataBinding callback will rebuild when the state(count) change.

class _HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final viewModel = context.viewModel<HomeViewModel>();
    return Scaffold(
      appBar: AppBar(
        title: const Text('Just'),
      ),
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            // binding state : count
            DataBinding(
              () => Text(
                'count: ${viewModel.count.value}',
                style: const TextStyle(fontSize: 20),
              ),
            ),
            const SizedBox(height: 10),
            // binding state : now
            DataBinding(
              () => Text(
                'now: ${viewModel.now.value.millisecondsSinceEpoch}',
                style: const TextStyle(fontSize: 20),
              ),
            ),
            const SizedBox(height: 10),
            // binding state : name and age
            DataBinding(
              () => Column(
                children: [
                  Text(
                    'name: ${viewModel.name.value}',
                    style: const TextStyle(fontSize: 20),
                  ),
                  const SizedBox(width: 10),
                  Text(
                    'age: ${viewModel.age.value}',
                    style: const TextStyle(fontSize: 20),
                  ),
                ],
              ),
            ),
            const SizedBox(height: 10),
            Column(
              children: [
                FilledButton(
                  onPressed: () {
                    viewModel.increment();
                  },
                  child: const Text("increment"),
                ),
                FilledButton(
                  onPressed: () {
                    viewModel.syncTime();
                  },
                  child: const Text("syncTime"),
                ),
                FilledButton(
                  onPressed: () {
                    viewModel.syncUserInfo();
                  },
                  child: const Text("syncUserInfo"),
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }
}

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