Overview

The SPEventDispatcher class is the base for all classes that dispatch events.

The event mechanism is a key feature of Sparrow’s architecture. Objects can communicate with each other through events.

An event dispatcher can dispatch events (objects of type SPEvent or one of its subclasses) to objects that have registered themselves as listeners. A string (the event type) is used to identify different events.

Here is a sample:

// dispatching an event
[self dispatchEvent:[SPEvent eventWithType:@"eventType"]];

// listening to an event from 'object'
[object addEventListener:@selector(onEvent:) atObject:self forType:@"eventType"];

// the corresponding event listener
- (void)onEvent:(SPEvent *)event
{
    // an event was triggered
}

Alternatively, you can use blocks as event listeners:

[object addEventListenerForType:@"eventType" block:^(SPEvent *event)
 {
     // the event was triggered
 }];

Since SPDisplayObject (the base class of all rendered objects) inherits from SPEventDispatcher, the event mechanism is tightly bound to the display list. Events that have their bubbles-property enabled will rise up the display list until they reach its root (normally the stage). That means that a listener can register for the event type not only on the object that will dispatch it, but on any object that is a direct or indirect parent of the dispatcher.

Different to Adobe Flash, events in Sparrow do not have a capture-phase.