EventBus

Simple event bus for event-driven programming. Taking advantage of kotlin language features instead of typical reflections

Table of Contents

• Installation
• Usage

Installation

• Build Tool
• From Source

Build Tool

If you are not using Gradle fallow the guide for other build tools on jitpack.io.

Gradle

Add https://www.jitpack.io as a maven repo to your project

repositories {
    maven { url 'https://www.jitpack.io' }
}

Then add the following dependency to your project

dependencies {
    implementation 'com.github.Zarzelcow:eventbus:-SNAPSHOT'
}

From Source

All code except dependencies is contained in one file Eventbus.kt

Dependencies are the Kotlin Standard Library and jodah's TypeTools

Usage

Unlike most 'conventional' annotation based event bus implementations, You instead register listeners on fields using kotlin functions

btw this still uses reflections, just not to call handlers

import com.github.zarzelcow.eventbus.Eventbus

val EVENT_BUS = EventBus()

class MyListener {

    @Handler
    val onKeypress = { event: EventKeypress ->
        println("Key pressed: ${event.key}")
    }

}

Btw. you can also create handlers like so if you don't need the event itself

@Handler(EventKeypress::class)
fun onKeypress() {
    println("A Key pressed")
}

This will register a listener on the event EventKeypress and will be called when the event is fired.

Events are completely normal java objects meaning you don't have to extend a type to publish anything

An example of an event is

    class EventKeypress(val key: Int)

To publish an event to all register listeners use code like this

fun `example publish`() {
    EVENT_BUS.publish(EventKeypress(key))
}

Registering the listener is done by calling subscribe with the instance of the class holding the listener

    EVENT_BUS.subscribe(MyListenerInstance)

To unregister a listener, call unsubscribe with the instance of the class holding the listener

    EVENT_BUS.unsubscribe(MyListenerInstance)

That gives you a simple event bus loop that you can use to publish events and subscribe to them in your code.

import com.github.zarzelcow.eventbus.Eventbus

val EVENT_BUS = EventBus()

class EventKeypress(val key: Int)
class MyListener {

    @Handler
    val onKeypress = { event: EventKeypress ->
        println("Key pressed: ${event.key}")
    }

}

fun main() {
    val MyListenerInstance = MyListener()
    EVENT_BUS.subscribe(MyListenerInstance)
    EVENT_BUS.publish(EventKeypress(1)) // prints "Key pressed: 1"
    EVENT_BUS.unsubscribe(MyListenerInstance)
}

Look at Test cases for some more examples