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/*******************************************************************************
* Copyright (c) 2009, 2016 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.common.utility.internal.model.value;
import java.util.EventListener;
import org.eclipse.jpt.common.utility.model.listener.PropertyChangeListener;
import org.eclipse.jpt.common.utility.model.value.PropertyValueModel;
import org.eclipse.jpt.common.utility.model.value.ModifiablePropertyValueModel;
/**
* This {@link AspectAdapter} provides basic property change support.
* This converts an "aspect" (as defined by subclasses) into
* a single {@link #VALUE} property.
* <p>
* The typical subclass will override the following methods:<ul>
* <li>{@link #engageSubject_()}<p>
* implement this method to add the appropriate listener to the subject
* <li>{@link #disengageSubject_()}<p>
* implement this method to remove the appropriate listener from the subject
* <li>{@link #buildValue_()}<p>
* at the very minimum, override this method to return the value of the
* subject's aspect (or "virtual" aspect); it does not need to be
* overridden if {@link #buildValue()} is overridden and its behavior changed
* <li>{@link #setValue_(Object)}<p>
* override this method if the client code needs to <em>set</em> the value of
* the subject's aspect; oftentimes, though, the client code (e.g. UI)
* will need only to <em>get</em> the value; it does not need to be
* overridden if {@link #setValue(Object)} is overridden and its behavior changed
* <li>{@link #buildValue()}<p>
* override this method only if returning a <code>null</code> value when
* the subject is <code>null</code> is unacceptable
* <li>{@link #setValue(Object)}<p>
* override this method only if something must be done when the subject
* is <code>null</code> (e.g. throw an exception)
* </ul>
* To notify listeners, subclasses can call {@link #aspectChanged()}
* whenever the aspect has changed.
*
* @param <S> the type of the model's subject
* @param <V> the type of the subject's property aspect
*/
public abstract class AspectPropertyValueModelAdapter<S, V>
extends AspectAdapter<S, V>
implements ModifiablePropertyValueModel<V>
{
/**
* Cache the current value of the aspect so we
* can pass an "old value" when we fire a property change event.
* We need this because the value may be calculated and may
* not be in the property change event fired by the subject,
* especially when dealing with multiple aspects.
*/
protected volatile V value;
// ********** constructor **********
/**
* Construct a property value model adapter for an aspect of the
* specified subject.
* The subject model cannot be <code>null</code>.
*/
protected AspectPropertyValueModelAdapter(PropertyValueModel<? extends S> subjectModel) {
super(subjectModel);
// our value is null when we are not listening to the subject
this.value = null;
}
// ********** PropertyValueModel implementation **********
/**
* Return the value of the subject's aspect.
*/
public final V getValue() {
return this.value;
}
// ********** WritablePropertyValueModel implementation **********
/**
* Set the value of the subject's aspect.
*/
public void setValue(V value) {
if (this.subject != null) {
this.setValue_(value);
}
}
/**
* Set the value of the subject's aspect.
* At this point we can be sure the {@link #subject} is
* <em>not</em> <code>null</code>.
* @see #setValue(Object)
*/
protected void setValue_(@SuppressWarnings("unused") V value) {
throw new RuntimeException("This method was not overridden."); //$NON-NLS-1$
}
// ********** AspectAdapter implementation **********
@Override
protected V getAspectValue() {
return this.value;
}
@Override
protected Class<? extends EventListener> getListenerClass() {
return PropertyChangeListener.class;
}
@Override
protected String getListenerAspectName() {
return VALUE;
}
@Override
public boolean hasListeners() {
return this.hasAnyPropertyChangeListeners(VALUE);
}
@Override
protected void fireAspectChanged(V oldValue, V newValue) {
this.firePropertyChanged(VALUE, oldValue, newValue);
}
@Override
protected void engageSubject() {
super.engageSubject();
// sync our value *after* we start listening to the subject,
// since its value might change when a listener is added
this.value = this.buildValue();
}
@Override
protected void disengageSubject() {
super.disengageSubject();
// clear out our value when we are not listening to the subject
this.value = null;
}
// ********** behavior **********
/**
* Return the aspect's value.
* At this point the subject may be <code>null</code>.
*/
protected V buildValue() {
return (this.subject == null) ? null : this.buildValue_();
}
/**
* Return the value of the subject's aspect.
* At this point we can be sure the {@link #subject} is
* <em>not</em> <code>null</code>.
* @see #buildValue()
*/
protected V buildValue_() {
throw new RuntimeException("This method was not overridden."); //$NON-NLS-1$
}
/**
* This method can be called by subclasses whenever the subject's aspect
* has changed; listeners will be notified appropriately.
*/
protected void aspectChanged() {
V old = this.value;
this.fireAspectChanged(old, this.value = this.buildValue());
}
@Override
public void toString(StringBuilder sb) {
sb.append(this.value);
}
}
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