Custom Events

You can write your own event classes and dispatch those events using the method described above. An event class must extend the AbstractEvent class, thus implementing the Event interface. Depending on the exact nature of the event, more interfaces should be implemented, like Cancellable for events that can be cancelled by a listener or interfaces like TargetPlayerEvent clarifying what sort of object is affected by your event.

Example: Custom Event Class

The following class describes an event indicating a Player has come in contact with FLARD and is now about to mutate in a way specified by the event. Since the event targets a player and can be cancelled by listeners, it implements both the TargetPlayerEvent and Cancellable interfaces.

Since generally custom events are intended to be listened to by other plugins, it is in your best interest to document them appropriately. This includes a list of objects typically found in the Cause. In the below example, it would probably be mentioned that the root cause is generally an object of the fictitious FLARDSource class.

import org.spongepowered.api.entity.living.player.Player;
import org.spongepowered.api.event.Cancellable;
import org.spongepowered.api.event.cause.Cause;
import org.spongepowered.api.event.entity.living.humanoid.player.TargetPlayerEvent;
import org.spongepowered.api.event.impl.AbstractEvent;

public class PlayerMutationEvent extends AbstractEvent implements TargetPlayerEvent, Cancellable {

    public enum Mutation {
        COMPULSIVE_POETRY,
        ROTTED_SOCKS,
        SPONTANEOUS_COMBUSTION;
    };

    private final Cause cause;
    private final Player victim;
    private final Mutation mutation;
    private boolean cancelled = false;

    public PlayerMutationEvent(Player victim, Mutation mutation, Cause cause) {
        this.victim = victim;
        this.mutation = mutation;
        this.cause = cause;
    }

    public Mutation getMutation() {
        return this.mutation;
    }

    @Override
    public boolean isCancelled() {
        return this.cancelled;
    }

    @Override
    public void setCancelled(boolean cancel) {
        this.cancelled = cancel;
    }

    @Override
    public Cause getCause() {
        return this.cause;
    }

    @Override
    public Player getTargetEntity() {
        return this.victim;
    }

}

Example: Fire Custom Event

import org.spongepowered.api.event.cause.Cause;
import org.spongepowered.api.event.cause.EventContext;
import org.spongepowered.api.event.cause.EventContextKeys;
import org.spongepowered.api.Sponge;

PluginContainer plugin = ...;
EventContext eventContext = EventContext.builder().add(EventContextKeys.PLUGIN, plugin).build();

PlayerMutationEvent event = new PlayerMutationEvent(victim, PlayerMutationEvent.Mutation.ROTTED_SOCKS,
        Cause.of(eventContext, plugin));
Sponge.getEventManager().post(event);
if (!event.isCancelled()) {
    // Mutation code
}

Bear in mind that you need to supply a non-empty cause. If your event was Cancellable, make sure that it was not cancelled before performing the action described by the event.

Example: Listen for Custom Event

import org.spongepowered.api.event.Listener;
import org.spongepowered.api.text.Text;

@Listener
public void onPrivateMessage(PlayerMutationEvent event) {
    if(event.getMutation() == PlayerMutationEvent.Mutation.SPONTANEOUS_COMBUSTION) {
        event.setCancelled(true);
        event.getTargetEntity().sendMessage(Text.of("You cannot combust here, this is a non-smoking area!"));
    }
}