modelelement.java

mywork是rcp开发的很好的例子

/*******************************************************************************
 * Copyright (c) 2004, 2005 Elias Volanakis and others.
�* 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:
�*����Elias Volanakis - initial API and implementation
�*******************************************************************************/
package net.sf.freenote.model;

import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;

import org.eclipse.ui.views.properties.IPropertyDescriptor;
import org.eclipse.ui.views.properties.IPropertySource;

/**
 * Abstract prototype of a model element.
 * <p>This class provides features necessary for all model elements, like:</p>
 * <ul>
 * <li>property-change support (used to notify edit parts of model changes),</li> 
 * <li>property-source support (used to display property values in the Property View) and</li>
 * </ul>
 * @author Elias Volanakis
 */
public abstract class ModelElement implements IPropertySource {
/** An empty property descriptor. */
private static final IPropertyDescriptor[] EMPTY_ARRAY = new IPropertyDescriptor[0];
/** Delegate used to implemenent property-change-support. */
private transient PropertyChangeSupport pcsDelegate;

/** 
 * Attach a non-null PropertyChangeListener to this object.
 * @param l a non-null PropertyChangeListener instance
 * @throws IllegalArgumentException if the parameter is null
 */
public synchronized void addPropertyChangeListener(PropertyChangeListener l) {
	if (l == null) {
		throw new IllegalArgumentException();
	}
	pcsDelegate().addPropertyChangeListener(l);
}

private PropertyChangeSupport pcsDelegate() {
	if(pcsDelegate == null)
		pcsDelegate = new PropertyChangeSupport(this);
	return pcsDelegate;
}

/** 
 * Report a property change to registered listeners (for example edit parts).
 * @param property the programmatic name of the property that changed
 * @param oldValue the old value of this property
 * @param newValue the new value of this property
 */
protected void firePropertyChange(String property, Object oldValue, Object newValue) {
	if (pcsDelegate().hasListeners(property)) {
		pcsDelegate().firePropertyChange(property, oldValue, newValue);
	}
}

/**
 * Returns a value for this property source that can be edited in a property sheet.
 * <p>My personal rule of thumb:</p>
 * <ul>
 * <li>model elements should return themselves and</li> 
 * <li>custom IPropertySource implementations (like DimensionPropertySource in the GEF-logic
 * example) should return an editable value.</li>
 * </ul>
 * <p>Override only if necessary.</p>
 * @return this instance
 */
public Object getEditableValue() {
	return this;
}

/**
 * Children should override this. The default implementation returns an empty array.
 */
public IPropertyDescriptor[] getPropertyDescriptors() {
	return EMPTY_ARRAY;
}

/**
 * Children should override this. The default implementation returns null.
 */
public Object getPropertyValue(Object id) {
	return null;
}

/**
 * Children should override this. The default implementation returns false.
 */
public boolean isPropertySet(Object id) {
	return false;
}

/** 
 * Remove a PropertyChangeListener from this component.
 * @param l a PropertyChangeListener instance
 */
public synchronized void removePropertyChangeListener(PropertyChangeListener l) {
	if (l != null) {
		pcsDelegate().removePropertyChangeListener(l);
	}
}

/**
 * Children should override this. The default implementation does nothing.
 */
public void resetPropertyValue(Object id) {
	// do nothing
}

/**
 * Children should override this. The default implementation does nothing.
 */
public void setPropertyValue(Object id, Object value) {
	// do nothing
}
}