com.google.gwt.event.logical.shared.ValueChangeEvent Maven / Gradle / Ivy
/*
* Copyright 2008 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.logical.shared;
import com.google.gwt.event.shared.GwtEvent;
/**
* Represents a value change event.
*
* @param the value about to be changed
*/
public class ValueChangeEvent extends GwtEvent> {
/**
* Handler type.
*/
private static Type> TYPE;
/**
* Fires a value change event on all registered handlers in the handler
* manager. If no such handlers exist, this method will do nothing.
*
* @param the old value type
* @param source the source of the handlers
* @param value the value
*/
public static void fire(HasValueChangeHandlers source, T value) {
if (TYPE != null) {
ValueChangeEvent event = new ValueChangeEvent(value);
source.fireEvent(event);
}
}
/**
* Fires value change event if the old value is not equal to the new value.
* Use this call rather than making the decision to short circuit yourself for
* safe handling of null.
*
* @param the old value type
* @param source the source of the handlers
* @param oldValue the oldValue, may be null
* @param newValue the newValue, may be null
*/
public static void fireIfNotEqual(HasValueChangeHandlers source,
T oldValue, T newValue) {
if (shouldFire(source, oldValue, newValue)) {
ValueChangeEvent event = new ValueChangeEvent(newValue);
source.fireEvent(event);
}
}
/**
* Gets the type associated with this event.
*
* @return returns the handler type
*/
public static Type> getType() {
if (TYPE == null) {
TYPE = new Type>();
}
return TYPE;
}
/**
* Convenience method to allow subtypes to know when they should fire a value
* change event in a null-safe manner.
*
* @param value type
* @param source the source
* @param oldValue the old value
* @param newValue the new value
* @return whether the event should be fired
*/
protected static boolean shouldFire(HasValueChangeHandlers source,
T oldValue, T newValue) {
return TYPE != null && oldValue != newValue
&& (oldValue == null || !oldValue.equals(newValue));
}
private final T value;
/**
* Creates a value change event.
*
* @param value the value
*/
protected ValueChangeEvent(T value) {
this.value = value;
}
// The instance knows its BeforeSelectionHandler is of type I, but the TYPE
// field itself does not, so we have to do an unsafe cast here.
@SuppressWarnings({"unchecked", "rawtypes"})
@Override
public final Type> getAssociatedType() {
return (Type) TYPE;
}
/**
* Gets the value.
*
* @return the value
*/
public T getValue() {
return value;
}
@Override
public String toDebugString() {
return super.toDebugString() + getValue();
}
@Override
protected void dispatch(ValueChangeHandler handler) {
handler.onValueChange(this);
}
}