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