Lindi

Lindi is a lightweight and reactive state management library for Flutter that simplifies building applications with dynamic UI updates. It enables developers to manage state using LindiViewModel and provides powerful widgets like LindiBuilder to listen and react to changes in state.

Features

• Easy state management with LindiViewModel.
• Reactivity using LindiBuilder for single and multiple states.
• Global dependency injection.
• Lightweight, intuitive, and easy to integrate.

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Installation

Add Lindi to your Flutter project by including it in your pubspec.yaml:

dependencies:
  lindi: latest_version

Then run:

flutter pub get

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Getting Started

1. Define a LindiViewModel

Create a class that extends LindiViewModel to manage your state:

class CounterLindiViewModel extends LindiViewModel {
  int counter = 0;

  void increment() {
    counter++;
    notify();
  }

  void decrement() {
    counter--;
    notify();
  }
}

Create a class that extends LindiViewModel<D, E> to manage your state:

class ApiLindiViewModel extends LindiViewModel<String, String> {

  void fetchData() async {
    setLoading();
    await Future.delayed(Duration(seconds: 4));
    setData('Fetched');
    await Future.delayed(Duration(seconds: 3));
    setError('Timeout!');
  }
}

• ApiLindiViewModel inherits from LindiViewModel<String, String>, where:
  • <D> represents the data type (in this case, API response data as String).
  • <E> represents the error type (in this case, error as String).

2. Register Your LindiViewModel

Use injector to make the LindiViewModel accessible globally:

Lindi.inject([CounterLindiViewModel(), ApiLindiViewModel()]);

3. Use LindiBuilder

React to changes in a single LindiViewModel with LindiBuilder:

class CounterScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final counterViewModel = Lindi.get<CounterLindiViewModel>();

    return Scaffold(
      body: Center(
        child: LindiBuilder(
          viewModels: [counterViewModel],
          builder: (context) {
            return Text(
              'Counter: ${counterViewModel.counter}',
              style: const TextStyle(fontSize: 24),
            );
          },
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: counterViewModel.increment,
        child: const Icon(Icons.add),
      ),
    );
  }
}

React to changes in a single LindiViewModel<D, E> with LindiBuilder:

class ApiScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final apiViewModel = Lindi.get<ApiLindiViewModel>();

    return Scaffold(
      body: Center(
        child: LindiBuilder(
          viewModels: [apiViewModel],
          builder: (context) {
            if(apiViewModel.isLoading){
              return CircularProgressIndicator();
            }
            if(apiViewModel.hasError){
              return Text(apiViewModel.error!);
            }
            return Text(apiViewModel.data!);
          },
        ),
      ),
    );
  }
}

4. Use LindiBuilder

Listen to multiple LindiViewModel instances simultaneously:

class ThemeLindiViewModel extends LindiViewModel {
  bool isDarkMode = false;

  void toggleTheme() {
    isDarkMode = !isDarkMode;
    notify();
  }
}

class MultiExampleScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final counterViewModel = Lindi.get<CounterLindiViewModel>();
    final themeViewModel = Lindi.get<ThemeLindiViewModel>();

    return Scaffold(
      body: LindiBuilder(
        viewModels: [counterViewModel, themeViewModel],
        listener: (context, viewModel) {
          if (viewModel is ThemeLindiViewModel) {
            if(themeViewModel.isDarkMode){
              debugPrint('Theme changed to dark mode');
            } else {
              debugPrint('Theme changed to light mode');
            }
          }
        },
        builder: (context) {
          return Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                Text(
                  'Counter: ${counterViewModel.counter}',
                  style: const TextStyle(fontSize: 24),
                ),
                const SizedBox(height: 20),
                ElevatedButton(
                  onPressed: counterViewModel.increment,
                  child: const Text('Increment Counter'),
                ),
                const SizedBox(height: 40),
                Text(
                  'Current Theme: ${themeViewModel.isDarkMode ? "Dark" : "Light"}',
                  style: const TextStyle(fontSize: 18),
                ),
                const SizedBox(height: 20),
                IconButton(
                  icon: Icon(
                    themeViewModel.isDarkMode ? Icons.dark_mode : Icons.light_mode,
                  ),
                  onPressed: themeViewModel.toggleTheme,
                ),
              ],
            ),
          );
        },
      ),
    );
  }
}

---

API Reference

LindiViewModel

• Extend this class to define your state management logic.
• Call notify() to update listeners when state changes.
• Call setLoading() to mark the LindiViewModel as loading and reset any previous error.
• Call setData(D data) to update the LindiViewModel with new data and stops loading.
• Call setError(E error) to store an error.

LindiBuilder

• Parameters:
  • viewModels: A list of LindiViewModel objects to listen to.
  • listener: A callback function that listens when the viewModel updates.
  • builder: A function that rebuilds the UI with the updated state.

Lindi

• Methods:
  • inject(List<LindiViewModel> instances): Inject a list of LindiViewModel instances.
  • T get<T extends LindiViewModel>(): Retrieves an injected LindiViewModel instance.

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Example Project

For a complete example, check out the example folder in the repository.

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License

This project is licensed under the MIT License - see the LICENSE file for details.

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Contributing

We welcome contributions! Feel free to submit issues or pull requests to improve Lindi.

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Happy coding with Lindi! 🚀