com.google.gwt.event.shared
Class EventBus

java.lang.Object
  com.google.gwt.event.shared.EventBus

All Implemented Interfaces:

HasHandlers

Direct Known Subclasses:

CountingEventBus, ResettableEventBus, SimpleEventBus

public abstract class EventBus
extends java.lang.Object
implements HasHandlers

Dispatches GwtEvents 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

EventBus

public EventBus()

addHandler

public abstract <H extends EventHandler> HandlerRegistration addHandler(GwtEvent.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 a GwtEvent subclass will provide a static register method, or a widget will accept handlers directly.

A tip: to make a handler de-register itself, the following works:

new MyHandler() {
  HandlerRegistration reg = MyEvent.register(eventBus, this);
 
  public void onMyThing(MyEvent event) {
    /* do your thing */
    reg.removeHandler();
  }
 };
 

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 extends EventHandler> HandlerRegistration addHandlerToSource(GwtEvent.Type<H> type,
                                                                                java.lang.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 GwtEvent 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(GwtEvent<?> event)

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

Specified by:

fireEvent in interface HasHandlers

Parameters:

event - the event to fire

fireEventFromSource

public abstract void fireEventFromSource(GwtEvent<?> event,
                                         java.lang.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