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/*******************************************************************************
* Copyright (c) 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.listener.PropertyChangeListener;
import org.eclipse.jpt.utility.model.value.PropertyValueModel;
/**
* This abstract class provides the infrastructure needed to wrap
* a value model, "lazily" listen to it, and convert
* its change notifications into property value model change
* notifications.
*
* Subclasses must override:
* - #buildValue()
* to return the current property value, as derived from the
* current model value
*
*/
public abstract class AspectPropertyValueModelAdapter<T>
extends AbstractModel
implements PropertyValueModel<T>
{
/**
* Cache the current value so we can pass an "old value" when
* we fire a property change event.
* We need this because the value may be calculated and we may
* not able to derive the "old value" from the collection
* change event fired by the collection value model.
*/
protected T value;
// ********** constructor/initialization **********
protected AspectPropertyValueModelAdapter() {
super();
// our value is null when we are not listening to the collection holder
this.value = null;
}
@Override
protected ChangeSupport buildChangeSupport() {
return new SingleAspectChangeSupport(this, PropertyChangeListener.class, VALUE);
}
// ********** PropertyValueModel implementation **********
/**
* Return the cached value.
*/
public T getValue() {
return this.value;
}
// ********** extend change support **********
/**
* Extend to start listening to the wrapped collection if necessary.
*/
@Override
public synchronized void addPropertyChangeListener(PropertyChangeListener listener) {
if (this.hasNoListeners()) {
this.engageModel();
}
super.addPropertyChangeListener(listener);
}
/**
* Extend to start listening to the wrapped collection if necessary.
*/
@Override
public synchronized void addPropertyChangeListener(String propertyName, PropertyChangeListener listener) {
if (propertyName == VALUE && this.hasNoListeners()) {
this.engageModel();
}
super.addPropertyChangeListener(propertyName, listener);
}
/**
* Extend to stop listening to the wrapped collection if necessary.
*/
@Override
public synchronized void removePropertyChangeListener(PropertyChangeListener listener) {
super.removePropertyChangeListener(listener);
if (this.hasNoListeners()) {
this.disengageModel();
}
}
/**
* Extend to stop listening to the wrapped collection if necessary.
*/
@Override
public synchronized void removePropertyChangeListener(String propertyName, PropertyChangeListener listener) {
super.removePropertyChangeListener(propertyName, listener);
if (propertyName == VALUE && this.hasNoListeners()) {
this.disengageModel();
}
}
// ********** queries **********
/**
* Return whether there are any listeners for the aspect.
*/
protected boolean hasListeners() {
return this.hasAnyPropertyChangeListeners(VALUE);
}
/**
* Return whether there are any listeners for the aspect.
*/
protected boolean hasNoListeners() {
return ! this.hasListeners();
}
// ********** behavior **********
/**
* Start listening to the model and build the value.
*/
protected void engageModel() {
this.engageModel_();
// synch our value *after* we start listening to the collection,
// since the collection's value might change when a listener is added
this.value = this.buildValue();
}
/**
* Start listening to the model.
*/
protected abstract void engageModel_();
/**
* Build and return the current value, as derived from the
* current state of the wrapped model.
*/
protected abstract T buildValue();
/**
* Stop listening to the model and clear the value.
*/
protected void disengageModel() {
this.disengageModel_();
// clear out our value when we are not listening to the collection
this.value = null;
}
/**
* Stop listening to the model.
*/
protected abstract void disengageModel_();
/**
* The wrapped model changed in some fashion.
* Recalculate the value and notify any listeners.
*/
protected void propertyChanged() {
Object old = this.value;
this.value = this.buildValue();
this.firePropertyChanged(VALUE, old, this.value);
}
}
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