Events

Simple asynchronous events for Kotlin

Requirements

• JDK 17

Download

The library is available in the Central Repository.

repositories {
    mavenCentral()
}

dependencies {
    implementation("io.v47:events:3.0.0")
}

How-To

This rather simple event library only has two important interfaces: EventKey and EventEmitter.

EventKey is used to uniquely identify an event type and is type-bound to its payload which can be anything.

import io.v47.events.EventKey

data class StringEvent(val message: String) {
    companion object : EventKey<StringEvent>
}

In this case StringEvent is the payload and its companion object is the appropriate event key.

This can now be used with the EventEmitter interface to emit it.

Events provides a default implementation of EventEmitter, DefaultEventEmitter which can be subclassed or delegated to for all your event emitting needs.

The emit function of EventEmitter is suspending which means that it's going to run in the current coroutine context. This gives you full control over how to emit events, whether to block the current coroutine until all listeners were called, or to launch a new coroutine just to emit the events.

import io.v47.events.DefaultEventEmitter
import kotlinx.coroutines.runBlocking

fun main() = runBlocking {
    val emitter = DefaultEventEmitter()
    
    // You can either add a permanent listener...
    emitter.on(StringEvent) {
        println(it.message)
    }
    
    // ...or one that's only called once and then discarded
    emitter.once(StringEvent) {
        println(it.message)
    }
    
    emitter.emit(StringEvent, StringEvent("This is printed twice")) // suspending
    emitter.emit(StringEvent, StringEvent("This is printed once")) // suspending
}

The expected output is:

This is printed twice
This is printed twice
This is printed once

License

Events is released under the terms of the BSD 3-clause-clear license