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/*******************************************************************************
* Copyright (c) 2007, 2008 Oracle. All rights reserved.
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v1.0, which accompanies this distribution
* and is available at http://www.eclipse.org/legal/epl-v10.html.
*
* Contributors:
* Oracle - initial API and implementation
******************************************************************************/
package org.eclipse.jpt.utility.internal.model.value;
import org.eclipse.jpt.utility.internal.model.ChangeSupport;
import org.eclipse.jpt.utility.model.event.PropertyChangeEvent;
import org.eclipse.jpt.utility.model.listener.StateChangeListener;
import org.eclipse.jpt.utility.model.value.WritablePropertyValueModel;
/**
* Abstract model that provides behavior for wrapping a property
* value model and listening for changes to aspects of the *value* contained
* by the property value model. Changes to the actual value are also monitored.
*
* This is useful if you have a value that may change, but whose aspects can also
* change in a fashion that might be of interest to the client.
*
* NB: Clients will need to listen for two different change notifications: a property
* change event will be be fired when the value changes; a state change event
* will be fired when an aspect of the value changes.
*
* Subclasses need to override two methods:
*
* #engageValue_()
* begin listening to the appropriate aspect of the value and call
* #valueAspectChanged(Object) whenever the aspect changes
*
* #disengageValue_()
* stop listening to the appropriate aspect of the value
*/
public abstract class ValueAspectAdapter<T>
extends PropertyValueModelWrapper<T>
implements WritablePropertyValueModel<T>
{
/** Cache the value so we can disengage. Null until we have a listener*/
protected T value;
// ********** constructors/initialization **********
/**
* Constructor - the value holder is required.
*/
protected ValueAspectAdapter(WritablePropertyValueModel<T> valueHolder) {
super(valueHolder);
}
/**
* Override to allow both property value model change and state change
* listeners.
*/
@Override
protected ChangeSupport buildChangeSupport() {
return new ChangeSupport(this);
}
// ********** PropertyValueModel implementation **********
public T getValue() {
return this.value;
}
// ********** WritablePropertyValueModel implementation **********
public void setValue(T value) {
this.valueHolder().setValue(value);
}
// ********** PropertyValueModelWrapper implementation **********
@Override
protected void valueChanged(PropertyChangeEvent event) {
this.disengageValue();
this.engageValue();
this.firePropertyChanged(event.cloneWithSource(this));
}
// ********** extend change support **********
@Override
public synchronized void addStateChangeListener(StateChangeListener listener) {
if (this.hasNoStateChangeListeners()) {
this.engageValue();
}
super.addStateChangeListener(listener);
}
@Override
public synchronized void removeStateChangeListener(StateChangeListener listener) {
super.removeStateChangeListener(listener);
if (this.hasNoStateChangeListeners()) {
this.disengageValue();
}
}
// ********** behavior **********
/**
* Start listening to the current value.
*/
protected void engageValue() {
this.value = this.valueHolder.getValue();
if (this.value != null) {
this.engageValue_();
}
}
/**
* Start listening to the current value.
* At this point we can be sure that the value is not null.
*/
protected abstract void engageValue_();
/**
* Stop listening to the current value.
*/
protected void disengageValue() {
if (this.value != null) {
this.disengageValue_();
this.value = null;
}
}
/**
* Stop listening to the current value.
* At this point we can be sure that the value is not null.
*/
protected abstract void disengageValue_();
/**
* Subclasses should call this method whenever the value's aspect changes.
*/
protected void valueAspectChanged() {
this.fireStateChanged();
}
/**
* Our constructors accept only a WritablePropertyValueModel<T1>.
*/
@SuppressWarnings("unchecked")
protected WritablePropertyValueModel<T> valueHolder() {
return (WritablePropertyValueModel<T>) this.valueHolder;
}
}
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