| /******************************************************************************* |
| * Copyright (c) 2005, 2007 IBM Corporation 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: |
| * IBM Corporation - initial API and implementation |
| * Brad Reynolds - bug 116920 |
| * Brad Reynolds - bug 147515 |
| *******************************************************************************/ |
| package org.eclipse.core.databinding.observable.value; |
| |
| import org.eclipse.core.databinding.observable.ChangeEvent; |
| import org.eclipse.core.databinding.observable.IChangeListener; |
| import org.eclipse.core.databinding.observable.IObservable; |
| import org.eclipse.core.databinding.observable.IStaleListener; |
| import org.eclipse.core.databinding.observable.ObservableTracker; |
| import org.eclipse.core.databinding.observable.Realm; |
| import org.eclipse.core.databinding.observable.StaleEvent; |
| |
| /** |
| * A Lazily calculated value that automatically computes and registers listeners |
| * on its dependencies as long as all of its dependencies are IObservable |
| * objects |
| * <p> |
| * This class is thread safe. All state accessing methods must be invoked from |
| * the {@link Realm#isCurrent() current realm}. Methods for adding and removing |
| * listeners may be invoked from any thread. |
| * </p> |
| * @since 1.0 |
| */ |
| public abstract class ComputedValue extends AbstractObservableValue { |
| |
| private boolean dirty = true; |
| |
| private boolean stale = false; |
| |
| private Object cachedValue = null; |
| |
| /** |
| * Dependencies list. This is a collection that contains no duplicates. It |
| * is normally an ArrayList to conserve memory, but if it ever grows above a |
| * certain number of elements, a HashSet is substited to conserve runtime. |
| */ |
| private IObservable[] dependencies = new IObservable[0]; |
| |
| /** |
| * |
| */ |
| public ComputedValue() { |
| this(Realm.getDefault(), null); |
| } |
| |
| /** |
| * @param valueType can be <code>null</code> |
| */ |
| public ComputedValue(Object valueType) { |
| this(Realm.getDefault(), valueType); |
| } |
| |
| /** |
| * @param realm |
| * |
| */ |
| public ComputedValue(Realm realm) { |
| this(realm, null); |
| } |
| |
| /** |
| * @param realm |
| * @param valueType |
| */ |
| public ComputedValue(Realm realm, Object valueType) { |
| super(realm); |
| this.valueType = valueType; |
| } |
| |
| /** |
| * Inner class that implements interfaces that we don't want to expose as |
| * public API. Each interface could have been implemented using a separate |
| * anonymous class, but we combine them here to reduce the memory overhead |
| * and number of classes. |
| * |
| * <p> |
| * The Runnable calls computeValue and stores the result in cachedValue. |
| * </p> |
| * |
| * <p> |
| * The IChangeListener stores each observable in the dependencies list. |
| * This is registered as the listener when calling ObservableTracker, to |
| * detect every observable that is used by computeValue. |
| * </p> |
| * |
| * <p> |
| * The IChangeListener is attached to every dependency. |
| * </p> |
| * |
| */ |
| private class PrivateInterface implements Runnable, IChangeListener, |
| IStaleListener { |
| public void run() { |
| cachedValue = calculate(); |
| } |
| |
| public void handleStale(StaleEvent event) { |
| if (!dirty && !stale) { |
| stale = true; |
| fireStale(); |
| } |
| } |
| |
| public void handleChange(ChangeEvent event) { |
| makeDirty(); |
| } |
| } |
| |
| private PrivateInterface privateInterface = new PrivateInterface(); |
| |
| private Object valueType; |
| |
| protected final Object doGetValue() { |
| if (dirty) { |
| // This line will do the following: |
| // - Run the calculate method |
| // - While doing so, add any observable that is touched to the |
| // dependencies list |
| IObservable[] newDependencies = ObservableTracker.runAndMonitor( |
| privateInterface, privateInterface, null); |
| |
| stale = false; |
| for (int i = 0; i < newDependencies.length; i++) { |
| IObservable observable = newDependencies[i]; |
| // Add a change listener to the new dependency. |
| if (observable.isStale()) { |
| stale = true; |
| } else { |
| observable.addStaleListener(privateInterface); |
| } |
| } |
| |
| dependencies = newDependencies; |
| |
| dirty = false; |
| } |
| |
| return cachedValue; |
| } |
| |
| /** |
| * Subclasses must override this method to provide the object's value. |
| * |
| * @return the object's value |
| */ |
| protected abstract Object calculate(); |
| |
| protected final void makeDirty() { |
| if (!dirty) { |
| dirty = true; |
| |
| stopListening(); |
| |
| // copy the old value |
| final Object oldValue = cachedValue; |
| // Fire the "dirty" event. This implementation recomputes the new |
| // value lazily. |
| fireValueChange(new ValueDiff() { |
| |
| public Object getOldValue() { |
| return oldValue; |
| } |
| |
| public Object getNewValue() { |
| return getValue(); |
| } |
| }); |
| } |
| } |
| |
| /** |
| * |
| */ |
| private void stopListening() { |
| // Stop listening for dependency changes. |
| for (int i = 0; i < dependencies.length; i++) { |
| IObservable observable = dependencies[i]; |
| |
| observable.removeChangeListener(privateInterface); |
| observable.removeStaleListener(privateInterface); |
| } |
| } |
| |
| public boolean isStale() { |
| // we need to recompute, otherwise staleness wouldn't mean anything |
| getValue(); |
| return stale; |
| } |
| |
| public Object getValueType() { |
| return valueType; |
| } |
| |
| public synchronized void addChangeListener(IChangeListener listener) { |
| super.addChangeListener(listener); |
| // If somebody is listening, we need to make sure we attach our own |
| // listeners |
| getValue(); |
| } |
| |
| public synchronized void addValueChangeListener(IValueChangeListener listener) { |
| super.addValueChangeListener(listener); |
| // If somebody is listening, we need to make sure we attach our own |
| // listeners |
| getValue(); |
| } |
| |
| public synchronized void dispose() { |
| super.dispose(); |
| stopListening(); |
| } |
| |
| } |