Package com.google.web.bindery.event.shared

Class EventBus

java.lang.Object

com.google.web.bindery.event.shared.EventBus

Direct Known Subclasses:

CountingEventBus, EventBus, RecordingEventBus, ResettableEventBus, SimpleEventBus

public abstract class EventBus
extends Object

Dispatches Events to interested parties. Eases decoupling by allowing objects to interact without having direct dependencies upon one another, and without requiring event sources to deal with maintaining handler lists. There will typically be one EventBus per application, broadcasting events that may be of general interest.

See Also:

• SimpleEventBus
• ResettableEventBus
• CountingEventBus

Constructor Summary

Constructors

Constructor	Description
EventBus()

Method Summary

Modifier and Type	Method	Description
abstract <H> HandlerRegistration	addHandler(Event.Type<H> type, H handler)	Adds an unfiltered handler to receive events of this type from all sources.
abstract <H> HandlerRegistration	addHandlerToSource(Event.Type<H> type, Object source, H handler)	Adds a handler to receive events of this type from the given source.
protected static <H> void	dispatchEvent(Event<H> event, H handler)	Invokes event.dispatch with handler.
abstract void	fireEvent(Event<?> event)	Fires the event from no source.
abstract void	fireEventFromSource(Event<?> event, Object source)	Fires the given event to the handlers listening to the event's type.
protected static void	setSourceOfEvent(Event<?> event, Object source)	Sets source as the source of event.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

EventBus

public EventBus()

Method Details

dispatchEvent

protected static <H> void dispatchEvent(Event<H> event,
 H handler)

Invokes event.dispatch with handler.

Protected to allow EventBus implementations in different packages to dispatch events even though the event.dispatch method is protected.

setSourceOfEvent

protected static void setSourceOfEvent(Event<?> event,
 Object source)

Sets source as the source of event.

Protected to allow EventBus implementations in different packages to set an event source even though the event.setSource method is protected.

addHandler

public abstract <H> HandlerRegistration addHandler(Event.Type<H> type,
 H handler)

Adds an unfiltered handler to receive events of this type from all sources.

It is rare to call this method directly. More typically an Event subclass will provide a static register method, or a widget will accept handlers directly.

Type Parameters:

H - The type of handler

Parameters:

type - the event type associated with this handler

handler - the handler

Returns:

the handler registration, can be stored in order to remove the handler later

addHandlerToSource

public abstract <H> HandlerRegistration addHandlerToSource(Event.Type<H> type,
 Object source,
 H handler)

Adds a handler to receive events of this type from the given source.

It is rare to call this method directly. More typically a Event subclass will provide a static register method, or a widget will accept handlers directly.

Type Parameters:

H - The type of handler

Parameters:

type - the event type associated with this handler

source - the source associated with this handler

handler - the handler

Returns:

the handler registration, can be stored in order to remove the handler later

fireEvent

public abstract void fireEvent(Event<?> event)

Fires the event from no source. Only unfiltered handlers will receive it.

Any exceptions thrown by handlers will be bundled into a UmbrellaException and then re-thrown after all handlers have completed. An exception thrown by a handler will not prevent other handlers from executing.

Parameters:

event - the event to fire

Throws:

UmbrellaException - wrapping exceptions thrown by handlers

fireEventFromSource

public abstract void fireEventFromSource(Event<?> event,
 Object source)

Fires the given event to the handlers listening to the event's type.

Any exceptions thrown by handlers will be bundled into a UmbrellaException and then re-thrown after all handlers have completed. An exception thrown by a handler will not prevent other handlers from executing.

Parameters:

event - the event to fire

Throws:

UmbrellaException - wrapping exceptions thrown by handlers