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/*******************************************************************************
* Copyright (c) 2008, 2010 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 org.eclipse.jpt.common.utility.model.value.PropertyValueModel;
/**
* This abstract class provides the infrastructure needed to wrap
* a model, "lazily" listen to it, and convert
* its change notifications into property value model change
* notifications.
* <p>
* Subclasses must implement:<ul>
* <li>{@link #buildValue()}<p>
* to return the current property value, as derived from the
* current model
* <li>{@link #engageModel_()}<p>
* to start listening to the adapted model
* <li>{@link #disengageModel_()}<p>
* to stop listening to the adapted model
* </ul>
* Subclasses can call {@link #propertyChanged()} whenever the calculated
* value of the property changes (as determined by the subclass).
*/
public abstract class AbstractPropertyValueModelAdapter<V>
extends AbstractPropertyValueModel
implements PropertyValueModel<V>
{
/**
* 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 any fired events.
*/
protected V value;
// ********** constructor/initialization **********
protected AbstractPropertyValueModelAdapter() {
super();
// our value is null when we are not listening to the model
this.value = null;
}
// ********** PropertyValueModel implementation **********
/**
* Return the cached value.
*/
public V getValue() {
return this.value;
}
// ********** behavior **********
/**
* Start listening to the model and build the value.
*/
@Override
protected void engageModel() {
this.engageModel_();
// synch our value *after* we start listening to the model,
// since the model'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 underlying model.
*/
protected abstract V buildValue();
/**
* Stop listening to the model and clear the value.
*/
@Override
protected void disengageModel() {
this.disengageModel_();
// clear out our value when we are not listening to the model
this.value = null;
}
/**
* Stop listening to the model.
*/
protected abstract void disengageModel_();
/**
* The underlying model changed in some fashion.
* Recalculate the value and notify any listeners.
*/
protected void propertyChanged() {
Object old = this.value;
this.firePropertyChanged(VALUE, old, this.value = this.buildValue());
}
@Override
public void toString(StringBuilder sb) {
sb.append(this.value);
}
}
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