com.google.gwt.event.shared.GwtEvent Maven / Gradle / Ivy
/*
* Copyright 2009 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.gwt.event.shared;
/**
* Root of all GWT events. All GWT events are considered dead and should no
* longer be accessed once the {@link HandlerManager} which originally fired the
* event finishes with it. That is, don't hold on to event objects outside of
* your handler methods.
*
* @param handler type
*
*/
public abstract class GwtEvent {
/**
* Type class used to register events with the {@link HandlerManager}.
*
* Type is parameterized by the handler type in order to make the addHandler
* method type safe.
*
*
* @param handler type
*/
public static class Type {
private static int nextHashCode;
private final int index;
/**
* Constructor.
*/
public Type() {
index = ++nextHashCode;
}
// We override hash code to make it as efficient as possible.
@Override
public final int hashCode() {
return index;
}
@Override
public String toString() {
return "Event type";
}
}
private boolean dead;
private Object source;
/**
* Constructor.
*/
protected GwtEvent() {
}
/**
* Returns the type used to register this event. Used by handler manager to
* dispatch events to the correct handlers.
*
* @return the type
*/
public abstract Type getAssociatedType();
/**
* Returns the source that last fired this event.
*
* @return object representing the source of this event
*/
public Object getSource() {
assertLive();
return source;
}
/**
* This is a method used primarily for debugging. It gives a string
* representation of the event details. This does not override the toString
* method because the compiler cannot always optimize toString out correctly.
* Event types should override as desired.
*
* @return a string representing the event's specifics.
*/
public String toDebugString() {
String name = this.getClass().getName();
name = name.substring(name.lastIndexOf(".") + 1);
return "event: " + name + ":";
}
/**
* The toString() for abstract event is overridden to avoid accidently
* including class literals in the the compiled output. Use {@link GwtEvent}
* #toDebugString to get more information about the event.
*/
@Override
public String toString() {
return "An event type";
}
/**
* Asserts that the event still should be accessed. All events are considered
* to be "dead" after their original handler manager finishes firing them. An
* event can be revived by calling {@link GwtEvent#revive()}.
*/
protected void assertLive() {
assert (!dead) : "This event has already finished being processed by its original handler manager, so you can no longer access it";
}
/**
* Should only be called by {@link HandlerManager}. In other words, do not use
* or call.
*
* @param handler handler
*/
protected abstract void dispatch(H handler);
/**
* Is the event current live?
*
* @return whether the event is live
*/
protected final boolean isLive() {
return !dead;
}
/**
* Kill the event. After the event has been killed, users cannot really on its
* values or functions being available.
*/
protected void kill() {
dead = true;
source = null;
}
/**
* Revives the event. Used when recycling event instances.
*/
protected void revive() {
dead = false;
source = null;
}
/**
* Set the source that triggered this event.
*
* @param source the source of this event, should only be set by a
* {@link HandlerManager}
*/
void setSource(Object source) {
this.source = source;
}
}