How to subscribe to VS events

Learn how to subscribe to the custom Valkyrien Skies event system.

Introduction

Valkyrien Skies has its own loader-independent event system, with many useful events, such as "ship load" or "collision persist".

Usage is relatively straightforward.

Steps

Subscribing to the event

To subscribe to the event, you simply register a lambda using the vsCore singleton.

This can be done at any point in the mod lifecycle, but is commonly done in the mod constructor.

import org.valkyrienskies.mod.common.vsCore

fun init() {
    vsCore.shipLoadEvent.on { event ->
        println("Ship ${event.ship.id} loaded!")
    }
}

public MyMod() {
    ValkyrienSkiesMod.getApi().getShipLoadEvent().on((event) -> {
        System.out.println(
            "Ship "+event.getShip().getId()+" loaded!"
        );
    });
}

Abstracting the event

You don't have to pass an anonymous lambda, you can abstract it into a method and pass that instead.

import org.valkyrienskies.mod.common.vsCore

class MyMod {
    fun init() {
        vsCore.physTickEvent.on(::physTick)
    }

    private fun physTick(event: PhysTickEvent) {
        println("Physics tick!")
    }
}

public class MyMod {
    public MyMod() {
        ValkyrienSkiesMod.getApi().getPhysTickEvent()
            .on(this::physTick);
    }
    
    private void physTick(PhysTickEvent event) {
        System.out.println("Physics tick!");
    }
}

Unsubscribing from the event

In the rare case you want your listener to stop listening, you can use an overload of .on which takes two parameters.

The first parameter will be your event, the second will be a RegisteredListener. This RegisteredListener allows you to unsubscribe from the event.

The following example subscribes to the (physTick) event, fires a single time, then unsubscribes itself and will not trigger again.

import org.valkyrienskies.mod.common.vsCore

class MyMod {
    fun init() {
        vsCore.physTickEvent.on(::physTick)
    }

    private fun physTick(event: PhysTickEvent, handler: RegisteredListener) {
        println("Single physics tick")
        handler.unregister()
    }
}

public class MyMod {
    public MyMod() {
        ValkyrienSkiesMod.getApi().getPhysTickEvent()
            .on(this::physTick);
    }

    private void physTick(PhysTickEvent event, RegisteredListener handler) {
        System.out.println("Single physics tick");
        handler.unregister();
    }
}

Last modified: 01 October 2026