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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.AbstractModel;
import org.eclipse.jpt.utility.internal.model.ChangeSupport;
import org.eclipse.jpt.utility.internal.model.SingleAspectChangeSupport;
import org.eclipse.jpt.utility.model.event.PropertyChangeEvent;
import org.eclipse.jpt.utility.model.listener.PropertyChangeListener;
import org.eclipse.jpt.utility.model.value.PropertyValueModel;
/**
* This abstract class provides the infrastructure needed to wrap
* another property value model, "lazily" listen to it, and propagate
* its change notifications.
*/
public abstract class PropertyValueModelWrapper<T>
extends AbstractModel
{
/** The wrapped property value model. */
protected final PropertyValueModel<? extends T> valueHolder;
/** A listener that allows us to synch with changes to the wrapped value holder. */
protected final PropertyChangeListener valueChangeListener;
// ********** constructors/initialization **********
/**
* Construct a property value model with the specified wrapped
* property value model. The value holder is required.
*/
protected PropertyValueModelWrapper(PropertyValueModel<? extends T> valueHolder) {
super();
if (valueHolder == null) {
throw new NullPointerException();
}
this.valueHolder = valueHolder;
this.valueChangeListener = this.buildValueChangeListener();
}
@Override
protected ChangeSupport buildChangeSupport() {
return new SingleAspectChangeSupport(this, PropertyChangeListener.class, PropertyValueModel.VALUE);
}
protected PropertyChangeListener buildValueChangeListener() {
return new PropertyChangeListener() {
public void propertyChanged(PropertyChangeEvent event) {
PropertyValueModelWrapper.this.valueChanged(event);
}
@Override
public String toString() {
return "value change listener";
}
};
}
// ********** extend change support **********
/**
* Extend to start listening to the nested model if necessary.
*/
@Override
public synchronized void addPropertyChangeListener(PropertyChangeListener listener) {
if (this.hasNoPropertyChangeListeners(PropertyValueModel.VALUE)) {
this.engageValueHolder();
}
super.addPropertyChangeListener(listener);
}
/**
* Extend to start listening to the nested model if necessary.
*/
@Override
public synchronized void addPropertyChangeListener(String propertyName, PropertyChangeListener listener) {
if (propertyName == PropertyValueModel.VALUE && this.hasNoPropertyChangeListeners(PropertyValueModel.VALUE)) {
this.engageValueHolder();
}
super.addPropertyChangeListener(propertyName, listener);
}
/**
* Extend to stop listening to the nested model if necessary.
*/
@Override
public synchronized void removePropertyChangeListener(PropertyChangeListener listener) {
super.removePropertyChangeListener(listener);
if (this.hasNoPropertyChangeListeners(PropertyValueModel.VALUE)) {
this.disengageValueHolder();
}
}
/**
* Extend to stop listening to the nested model if necessary.
*/
@Override
public synchronized void removePropertyChangeListener(String propertyName, PropertyChangeListener listener) {
super.removePropertyChangeListener(propertyName, listener);
if (propertyName == PropertyValueModel.VALUE && this.hasNoPropertyChangeListeners(PropertyValueModel.VALUE)) {
this.disengageValueHolder();
}
}
// ********** behavior **********
/**
* Begin listening to the value holder.
*/
protected void engageValueHolder() {
this.valueHolder.addPropertyChangeListener(PropertyValueModel.VALUE, this.valueChangeListener);
}
/**
* Stop listening to the value holder.
*/
protected void disengageValueHolder() {
this.valueHolder.removePropertyChangeListener(PropertyValueModel.VALUE, this.valueChangeListener);
}
@Override
public void toString(StringBuilder sb) {
sb.append(this.valueHolder);
}
// ********** property change support **********
/**
* The value of the wrapped value holder has changed;
* propagate the change notification appropriately.
*/
protected abstract void valueChanged(PropertyChangeEvent event);
}
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