KStateMachine

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KStateMachine is a Kotlin DSL library for creating state machines and statecharts.

Overview

Integration features are:

• Kotlin DSL syntax. Declarative and clear state machine structure. Using without DSL is also possible.
• Kotlin Coroutines support. Call suspendable functions within the library. You can fully use KStateMachine without Kotlin Coroutines dependency if necessary.
• Kotlin Multiplatform support.
• Zero dependency. It is written in pure Kotlin, it does not depend on any third party libraries or Android SDK.

State management features:

• Event based - transitions are performed by processing incoming events
• Reactive - listen for machine, states, state groups and transitions
• Guarded and Conditional transitions - dynamic target state which is calculated in a moment of event processing depending on application business logic
• Nested states - build hierarchical state machines (statecharts) with cross-level transitions support
• **Composed (nested) state machines. ** Use state machines as atomic child states
• Pseudo states for additional logic in machine behaviour
• Typesafe transitions - pass data in typesafe way from event to state
• Parallel states - avoid a combinatorial explosion of states
• Undo transitions - navigate back to previous state
• Optional argument passing for events and transitions
• Export state machine structure to PlantUML and Mermaid diagrams
• Persist (serialize) state machine's active configuration and restore it later
• Logging - useful for debugging
• Testable - run state machine from specified state
• Well tested - all features are covered by tests

[!IMPORTANT] SEE FULL DOCUMENTATION HERE

Sponsors ❤

I highly appreciate that you donate or become a sponsor to support the project. Use ❤️ github-sponsors button to see supported methods and push the ⭐ star-button if you like this project.

Quick start sample

Finishing traffic light

stateDiagram-v2
    direction LR
    [*] --> GreenState
    GreenState --> YellowState: SwitchEvent
    YellowState --> RedState: SwitchEvent
    RedState --> [*]

object SwitchEvent : Event

sealed class States : DefaultState() {
    object GreenState : States()
    object YellowState : States()
    object RedState : States(), FinalState // Machine finishes when enters final state
}

fun main() = runBlocking {
    // Create state machine and configure its states in a setup block
    val machine = createStateMachine(this) {
        addInitialState(GreenState) {
            // Add state listeners
            onEntry { println("Enter green") }
            onExit { println("Exit green") }

            // Setup transition
            transition<SwitchEvent> {
                targetState = YellowState
                // Add transition listener
                onTriggered { println("Transition triggered") }
            }
        }

        addState(YellowState) {
            transition<SwitchEvent>(targetState = RedState)
        }

        addFinalState(RedState)

        onFinished { println("Finished") }
    }

    // Now we can process events
    machine.processEvent(SwitchEvent)
    machine.processEvent(SwitchEvent)
}

Samples

• Simple Android 2D shooter game sample

  The library itself does not depend on Android.

  

• Finished state sample

• Transition on FinishedEvent sample

• FinishedEvent using with DataState sample

• Undo transition sample

• PlantUML nested states export sample

• Mermaid nested states export sample

• PlantUML with MetaInfo export sample

• Inherit transitions by grouping states sample

• Minimal sealed classes sample

• Usage without Kotlin Coroutines sample

• Minimal syntax sample

• Guarded transition sample

• Cross-level transition sample

• Typesafe transition sample

• Complex syntax sample shows many syntax variants and library possibilities, so it looks messy

Install

KStateMachine is available on Maven Central and JitPack repositories.

See install section in the docs for details.

Maven Central

dependencies {
    // multiplatform artifacts, where <Tag> is a library version.
    implementation("io.github.nsk90:kstatemachine:<Tag>")
    implementation("io.github.nsk90:kstatemachine-coroutines:<Tag>")
}

Build

Run ./gradlew build or build with Intellij IDEA.

Contribution

The library is in a active development phase. You are welcome to propose useful features and contribute to the project. See CONTRIBUTING file.

Thanks to supporters

License

Licensed under permissive Boost Software License