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EventSystem.md

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Event System

Description

This component offers a simple and decoupled way for components to communicate. Events are defined given a function definition and a name and an ID is generated. Any number of subscribers can listen to events. Events can be queued and handled in batches to keep subscribers being notified at a controlled time.

Dependencies

  • None

Sub-Components

  • None

Terms

  • Event: A named function to dispatch to all subscribers
  • Event Listener: A prioritized subscriber
  • Event Listener List: A prioritized list of listeners for a specific event
  • Event System: The structure that allows creating events, listening to an event, and triggering events
  • Event Queued: An event to be queued for later processing

Design

class Event< L >

  • id: int
  • name: string

class EventListener< L >

  • priority: int
  • once: boolean
  • listener: L
  • stopped: boolean
  • next: EventListener< L >
  • muted: boolean
  • mute( muted: boolean ): boolean
  • remove(): boolean
  • stop(): void

class EventListenerList< L >

  • event: Event< L >
  • head: EventListener< L >
  • add( listener: L, once: boolean, priority: int = 5 ): EventListener< L >
  • clear(): void

class EventQueued< L >

  • event: Event< L >
  • arguments: object

class EventSystem

  • lists: EventListenerList[]
  • queued: Queue< EventQueued >
  • synchronous: boolean
  • create< L >( name: string ): Event< L >
  • on< L >( event: Event< L >, listener: L, priority: int = 5 ): EventListener< L >
  • once< L >( event: Event< L >, listener: L, priority: int = 5 ): EventListener< L >
  • queue< L >( event: Event< L > ): L
  • trigger< L >( event: Event< L > ): L
  • off< L >( event: Event< L > ): void
  • process(): int

interface HasEvents

  • getEvents(): EventSystem

Example

events = new EventSystem();

// ExplosionEvent( x, y )
// DeathEvent( player )

Event<ExplosionEvent> EXPLOSION = events.create( "explosion" );
Event<DeathEvent> DEATH = events.create( "death" );

listener = events.on( EXPLOSION, function(x, y) {
  // listen for explosions
});

// trigger explosion event
events.trigger( EXPLOSION )( 10, 4 );

// ignore event for now
listener.mute( true );

// ignore event forever
listener.remove();

// queue event
events.queue( DEATH )( myPlayer );

// process queued events
events.process()