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/*******************************************************************************
* Copyright (c) 2007 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.BidiFilter;
import org.eclipse.jpt.utility.internal.model.event.PropertyChangeEvent;
/**
* A <code>FilteringPropertyValueModel</code> wraps another
* <code>PropertyValueModel</code> and uses a <code>BidiFilter</code>
* to determine when the wrapped value is to be returned by calls
* to <code>value()</code> and modified by calls to
* <code>setValue(Object)</code>
* <p>
* As an alternative to building a <code>BidiFilter</code>, a subclass
* of <code>FilteringPropertyValueModel</code> can override the
* <code>accept(Object)</code> and <code>reverseAccept(Object)</code>
* methods.
* <p>
* One, possibly undesirable, side-effect of using this value model is that
* it must return *something* as the value. The default behavior is
* to return <code>null</code> whenever the wrapped value is not "accepted",
* which can be configured and/or overridden.
* <p>
* Likewise, if an incoming value is not "reverseAccepted", *nothing* will passed
* through to the wrapped value holder, not even <code>null</code>.
*/
public class FilteringPropertyValueModel
extends PropertyValueModelWrapper
{
private final BidiFilter filter;
private final Object defaultValue;
// ********** constructors **********
/**
* Construct a property value model with the specified nested
* property value model and a disabled filter.
* Use this constructor if you want to override the
* <code>accept(Object)</code> and <code>reverseAccept(Object)</code>
* methods instead of building a <code>BidiFilter</code>.
* The default value will be <code>null</code>.
*/
public FilteringPropertyValueModel(PropertyValueModel valueHolder) {
this(valueHolder, BidiFilter.Disabled.instance(), null);
}
/**
* Construct a property value model with the specified nested
* property value model, specified default value, and a disabled filter.
* Use this constructor if you want to override the
* <code>accept(Object)</code> and <code>reverseAccept(Object)</code>
* methods instead of building a <code>BidiFilter</code>
* <em>and</em> you need to specify
* a default value other than <code>null</code>.
*/
public FilteringPropertyValueModel(PropertyValueModel valueHolder, Object defaultValue) {
this(valueHolder, BidiFilter.Disabled.instance(), defaultValue);
}
/**
* Construct an property value model with the specified nested
* property value model and filter.
* The default value will be <code>null</code>.
*/
public FilteringPropertyValueModel(PropertyValueModel valueHolder, BidiFilter filter) {
this(valueHolder, filter, null);
}
/**
* Construct an property value model with the specified nested
* property value model, filter, and default value.
*/
public FilteringPropertyValueModel(PropertyValueModel valueHolder, BidiFilter filter, Object defaultValue) {
super(valueHolder);
this.filter = filter;
this.defaultValue = defaultValue;
}
// ********** ValueModel implementation **********
public Object value() {
return this.filterValue(this.valueHolder.value());
}
// ********** PropertyValueModel implementation **********
public void setValue(Object value) {
if (this.reverseAccept(value)) {
this.valueHolder.setValue(value);
}
}
// ********** PropertyValueModelWrapper implementation **********
@Override
protected void valueChanged(PropertyChangeEvent e) {
// filter the values before propagating the change event
Object oldValue = this.filterValue(e.oldValue());
Object newValue = this.filterValue(e.newValue());
this.firePropertyChanged(VALUE, oldValue, newValue);
}
// ********** queries **********
/**
* If the specified value is "accepted" simply return it,
* otherwise return the default value.
*/
protected Object filterValue(Object value) {
return this.accept(value) ? value : this.defaultValue();
}
/**
* Return whether the <code>FilteringPropertyValueModel</code> should
* return the specified value from a call to the
* <code>value()</code> method; the value came
* from the nested property value model
* <p>
* This method can be overridden by a subclass as an
* alternative to building a <code>BidiFilter</code>.
*/
protected boolean accept(Object value) {
return this.filter.accept(value);
}
/**
* Return whether the <code>FilteringPropertyValueModel</code>
* should pass through the specified value to the nested
* property value model in a call to the
* <code>setValue(Object)</code> method
* <p>
* This method can be overridden by a subclass as an
* alternative to building a <code>BidiFilter</code>.
*/
protected boolean reverseAccept(Object value) {
return this.filter.reverseAccept(value);
}
/**
* Return the object that should be returned if
* the nested value was rejected by the filter.
* The default is <code>null</code>.
*/
protected Object defaultValue() {
return this.defaultValue;
}
}
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