| /******************************************************************************* |
| * 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); |
| } |
| |
| } |