com.google.web.bindery.event.shared.binder.GenericEvent Maven / Gradle / Ivy
/*
* Copyright 2013 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.web.bindery.event.shared.binder;
import com.google.gwt.event.shared.GwtEvent;
import com.google.web.bindery.event.shared.binder.impl.GenericEventHandler;
import com.google.web.bindery.event.shared.binder.impl.GenericEventType;
/**
* Base class for all events fired on the event bus. Subclasses of this can be
* listened for in presenters using the {@link EventHandler} annotation.
*
* Events (subclasses of this class) should be very simple and immutable value
* types. In the simplest case for an event that takes no arguments, the body of
* the class can be entirely blank. In this case, the event is effectively just
* a tag that is never referenced directly after it is fired.
*
* In the slightly more complex case, events can take any number of arguments in
* their constructor. These arguments should be assigned to final fields for
* which public accessors should be exposed. Handlers can then access the
* arguments via the public methods. Events should rarely contains more logic
* than this and MUST be immutable. Since the same event is passed to each
* handler and the order in which the handlers will see the events is undefined,
* mutable events are very dangerous.
*
* A complete example of a single-argument event is shown below:
*
* public class ContactsLoadedEvent extends GenericEvent {
*
* private final List<Contacts> contacts;
*
* public PurchaseActionLoadedEvent(List<Contacts> contacts) {
* this.contacts = contacts;
* }
*
* public List<Contacts> getContacts() {
* return contacts;
* }
* }
*
*
* @author [email protected] (Erik Kuefler)
*/
public abstract class GenericEvent extends GwtEvent {
@Override
public GenericEventType getAssociatedType() {
return GenericEventType.getTypeOf(getClass());
}
@Override
protected void dispatch(GenericEventHandler handler) {
handler.handleEvent(this);
}
}