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What is Orbit

Orbit is a Redux/MVI-like library - but without the baggage. It's so simple we think of it as MVVM+.

• Simple, type-safe, coroutine-style, extensible API
• Multiplatform, targetting Android and iOS (iOS support is in alpha and being actively worked on)
• Full support for Kotlin Coroutines (it's built on top of them after all)
• Lifecycle-safe collection of infinite flows
• ViewModel support, along with SavedState
• Optional, simple unit test library
• Built-in espresso idling resource support
• Compatible with RxJava, LiveData etc. through coroutine wrappers
• And more...

Documentation

• Getting Started
• Core
• Android ViewModel
• Compose
• Test
• Dokka source code documentation
• Resources

Articles & Talks

• How to write your own MVI library and why you shouldn't
• Top Android MVI libraries in 2021

Getting started

implementation("org.orbit-mvi:orbit-core:<latest-version>")
// or, if on Android:
implementation("org.orbit-mvi:orbit-viewmodel:<latest-version>")
// If using Jetpack Compose include
implementation("org.orbit-mvi:orbit-compose:<latest-version>")

// Tests
testImplementation("org.orbit-mvi:orbit-test:<latest-version>")

Define the contract

data class CalculatorState(
    val total: Int = 0
)

sealed class CalculatorSideEffect {
    data class Toast(val text: String) : CalculatorSideEffect()
}

Create the ViewModel

1. Implement the ContainerHost interface
2. Override the container field and use the ViewModel.container factory function to build an Orbit Container in your ContainerHost

class CalculatorViewModel: ContainerHost<CalculatorState, CalculatorSideEffect>, ViewModel() {

    // Include `orbit-viewmodel` for the factory function
    override val container = container<CalculatorState, CalculatorSideEffect>(CalculatorState())

    fun add(number: Int) = intent {
        postSideEffect(CalculatorSideEffect.Toast("Adding $number to ${state.total}!"))

        reduce {
            state.copy(total = state.total + number)
        }
    }
}

We have used an Android ViewModel as the most common example, but there is no requirement to do so.

Connect to the ViewModel in your Activity or Fragment

class CalculatorActivity: AppCompatActivity() {

    // Example of injection using koin, your DI system might differ
    private val viewModel by viewModel<CalculatorViewModel>()

    override fun onCreate(savedState: Bundle?) {
        ...

        addButton.setOnClickListener { viewModel.add(1234) }

        viewModel.observe(state = ::render, sideEffect = ::handleSideEffect)
    }

    private fun render(state: CalculatorState) {
        ...
    }

    private fun handleSideEffect(sideEffect: CalculatorSideEffect) {
        when (sideEffect) {
            is CalculatorSideEffect.Toast -> toast(sideEffect.text)
        }
    }
}

With Jetpack Compose wire up the ViewModel as follows:

@Composable
fun CalculatorScreen(viewModel: CalculatorViewModel) {

    val state = viewModel.collectAsState().value

    viewModel.collectSideEffect { handleSideEffect(it) }

    // render UI using data from 'state'
    ...
}

private fun handleSideEffect(sideEffect: CalculatorSideEffect) {
    when (sideEffect) {
        is CalculatorSideEffect.Toast -> toast(sideEffect.text)
    }
}

Contributing

Please read contributing for details on our code of conduct, and the process for submitting pull requests to us.

Versioning

We use SemVer for versioning. For the versions available, see the tags on this repository.

License

This project is licensed under the Apache License, Version 2.0 - see the license file for details