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/*******************************************************************************
* 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.BidiTransformer;
import org.eclipse.jpt.utility.model.value.WritablePropertyValueModel;
/**
* A <code>CachingTransformationWritablePropertyValueModel<code> augments the
* behavior of a <code>TransformationWritablePropertyValueModel<code> by caching
* the transformed value.
* The transformed value is calculated and cached during initialization and every
* time the wrapped value changes. This can be useful when the old value
* passed in to <code>valueChanged(PropertyChangeEvent)</code> can no longer
* be "transformed" because its state is no longer valid.
* This caching can also improve time performance in some situations.
*/
public class CachingTransformationWritablePropertyValueModel<T1, T2>
extends TransformationWritablePropertyValueModel<T1, T2>
{
/**
* Cache the transformed value so that during property change event notification
* we do not have to transform the old value. The old value could no longer be valid in
* the model; as a result, transforming it would not be valid.
*/
protected T2 cachedValue;
// ********** constructors/initialization **********
/**
* Construct a writable property value model with the specified nested
* writable property value model and the default bidi transformer.
* Use this constructor if you want to override the
* <code>transform_(Object)</code> and <code>reverseTransform_(Object)</code>
* (or <code>transform(Object)</code> and <code>reverseTransform(Object)</code>)
* methods instead of building a <code>BidiTransformer</code>.
*/
public CachingTransformationWritablePropertyValueModel(WritablePropertyValueModel<T1> valueHolder) {
super(valueHolder);
}
/**
* Construct a writable property value model with the specified nested
* writable property value model and bidi transformer.
*/
public CachingTransformationWritablePropertyValueModel(WritablePropertyValueModel<T1> valueHolder, BidiTransformer<T1, T2> transformer) {
super(valueHolder, transformer);
}
// ********** behavior **********
/**
* We have listeners, transform the nested value and cache the result.
*/
@Override
protected void engageValueHolder() {
super.engageValueHolder();
this.cachedValue = this.transform(this.valueHolder.getValue());
}
/**
* We have no more listeners, clear the cached value.
*/
@Override
protected void disengageValueHolder() {
this.cachedValue = null;
super.disengageValueHolder();
}
/**
* No need to transform the nested value, simply return the cached value,
* which is already transformed.
*/
@Override
public T2 getValue() {
return this.cachedValue;
}
/**
* Transform the specified new value, caching it before returning it.
*/
@Override
protected T2 transformNew(T1 value) {
this.cachedValue = super.transformNew(value);
return this.cachedValue;
}
/**
* No need to transform the old value, simply return the cached value,
* which is already transformed.
*/
@Override
protected T2 transformOld(T1 value) {
return this.cachedValue;
}
}
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