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/*******************************************************************************
* Copyright (c) 2007 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 java.util.Collection;
import java.util.Iterator;
import org.eclipse.jpt.utility.internal.iterators.EmptyIterator;
import org.eclipse.jpt.utility.internal.iterators.SingleElementIterator;
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.internal.model.event.PropertyChangeEvent;
import org.eclipse.jpt.utility.internal.model.listener.CollectionChangeListener;
import org.eclipse.jpt.utility.internal.model.listener.PropertyChangeListener;
/**
* An adapter that allows us to make a PropertyValueModel behave like
* a read-only, single-element CollectionValueModel, sorta.
*
* If the property's value is null, an empty iterator is returned
* (i.e. you can't have a collection with a null element).
*/
public class PropertyCollectionValueModelAdapter
extends AbstractModel
implements CollectionValueModel
{
/** The wrapped property value model. */
protected final PropertyValueModel valueHolder;
/** A listener that forwards any events fired by the value holder. */
protected final PropertyChangeListener propertyChangeListener;
/** Cache the value. */
protected Object value;
// ********** constructors/initialization **********
/**
* Wrap the specified ListValueModel.
*/
public PropertyCollectionValueModelAdapter(PropertyValueModel valueHolder) {
super();
if (valueHolder == null) {
throw new NullPointerException();
}
this.valueHolder = valueHolder;
this.propertyChangeListener = this.buildPropertyChangeListener();
// postpone building the value and listening to the underlying value
// until we have listeners ourselves...
}
@Override
protected ChangeSupport buildChangeSupport() {
return new SingleAspectChangeSupport(this, VALUES);
}
/**
* The wrapped value has changed, forward an equivalent
* collection change event to our listeners.
*/
protected PropertyChangeListener buildPropertyChangeListener() {
return new PropertyChangeListener() {
public void propertyChanged(PropertyChangeEvent e) {
PropertyCollectionValueModelAdapter.this.valueChanged(e.newValue());
}
@Override
public String toString() {
return "property change listener";
}
};
}
// ********** CollectionValueModel implementation **********
public Iterator values() {
return (this.value == null) ?
EmptyIterator.instance()
:
new SingleElementIterator(this.value);
}
public void add(Object item) {
throw new UnsupportedOperationException();
}
public void addAll(Collection items) {
throw new UnsupportedOperationException();
}
public void remove(Object item) {
throw new UnsupportedOperationException();
}
public void removeAll(Collection items) {
throw new UnsupportedOperationException();
}
public int size() {
return (this.value == null) ? 0 : 1;
}
// ********** extend change support **********
/**
* Override to start listening to the value holder if necessary.
*/
@Override
public void addCollectionChangeListener(CollectionChangeListener listener) {
if (this.hasNoListeners()) {
this.engageModel();
}
super.addCollectionChangeListener(listener);
}
/**
* Override to start listening to the value holder if necessary.
*/
@Override
public void addCollectionChangeListener(String collectionName, CollectionChangeListener listener) {
if (collectionName == VALUES && this.hasNoListeners()) {
this.engageModel();
}
super.addCollectionChangeListener(collectionName, listener);
}
/**
* Override to stop listening to the value holder if appropriate.
*/
@Override
public void removeCollectionChangeListener(CollectionChangeListener listener) {
super.removeCollectionChangeListener(listener);
if (this.hasNoListeners()) {
this.disengageModel();
}
}
/**
* Override to stop listening to the value holder if appropriate.
*/
@Override
public void removeCollectionChangeListener(String collectionName, CollectionChangeListener listener) {
super.removeCollectionChangeListener(collectionName, listener);
if (collectionName == VALUES && this.hasNoListeners()) {
this.disengageModel();
}
}
// ********** queries **********
protected boolean hasListeners() {
return this.hasAnyCollectionChangeListeners(VALUES);
}
protected boolean hasNoListeners() {
return ! this.hasListeners();
}
// ********** behavior **********
protected void engageModel() {
this.valueHolder.addPropertyChangeListener(ValueModel.VALUE, this.propertyChangeListener);
// synch our value *after* we start listening to the value holder,
// since its value might change when a listener is added
this.value = this.valueHolder.value();
}
protected void disengageModel() {
this.valueHolder.removePropertyChangeListener(ValueModel.VALUE, this.propertyChangeListener);
// clear out the value when we are not listening to the value holder
this.value = null;
}
/**
* synchronize our internal value with the wrapped value
* and fire the appropriate events
*/
protected void valueChanged(Object newValue) {
// put in "empty" check so we don't fire events unnecessarily
if (this.value != null) {
Object oldValue = this.value;
this.value = null;
this.fireItemRemoved(VALUES, oldValue);
}
this.value = newValue;
// put in "empty" check so we don't fire events unnecessarily
if (this.value != null) {
this.fireItemAdded(VALUES, this.value);
}
}
@Override
public void toString(StringBuilder sb) {
sb.append(this.valueHolder);
}
}
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