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/*******************************************************************************
* Copyright (c) 2007, 2015 Matthew Hall and others.
*
* This program and the accompanying materials
* are made available under the terms of the Eclipse Public License 2.0
* which accompanies this distribution, and is available at
* https://www.eclipse.org/legal/epl-2.0/
*
* SPDX-License-Identifier: EPL-2.0
*
* Contributors:
* Matthew Hall - initial API and implementation (bug 180746)
* Boris Bokowski, IBM - initial API and implementation
* Matthew Hall - bugs 212223, 208332, 245647
* Will Horn - bug 215297
* Stefan Xenos <sxenos@gmail.com> - Bug 335792
******************************************************************************/
package org.eclipse.core.internal.databinding.observable;
import org.eclipse.core.databinding.observable.Diffs;
import org.eclipse.core.databinding.observable.IStaleListener;
import org.eclipse.core.databinding.observable.ObservableTracker;
import org.eclipse.core.databinding.observable.StaleEvent;
import org.eclipse.core.databinding.observable.value.AbstractObservableValue;
import org.eclipse.core.databinding.observable.value.IObservableValue;
import org.eclipse.core.databinding.observable.value.IValueChangeListener;
import org.eclipse.core.databinding.observable.value.IVetoableValue;
import org.eclipse.core.databinding.observable.value.ValueChangeEvent;
import org.eclipse.core.databinding.observable.value.ValueChangingEvent;
import org.eclipse.core.databinding.observable.value.ValueDiff;
/**
* {@link IObservableValue} implementation that wraps an
* {@link IObservableValue} and delays notification of value change events from
* the wrapped observable value until a certain time has passed since the last
* change event. This class helps to boost performance in bindings (both in
* validation and in event firing) when the observed value is rapidly changing.
* A common use of this class is to delay validation until the user stops typing
* in an UI field. To notify about pending changes, a DelayedObservableValue
* fires a stale event when the wrapped observable value fires a change event,
* and remains stale as long as a value change is pending.
*
* Note that this class will not forward {@link ValueChangingEvent} events from
* a wrapped {@link IVetoableValue}.
*
* @param <T>
* the type of the object being observed
*
* @since 1.2
*/
public class DelayedObservableValue<T> extends AbstractObservableValue<T>
implements IStaleListener, IValueChangeListener<T> {
class ValueUpdater implements Runnable {
private final T oldValue;
boolean cancel = false;
boolean running = false;
ValueUpdater(T oldValue) {
this.oldValue = oldValue;
}
void cancel() {
cancel = true;
}
@Override
public void run() {
if (!cancel)
try {
running = true;
internalFireValueChange(oldValue);
} finally {
running = false;
}
}
}
private final int delay;
private IObservableValue<T> observable;
private boolean dirty = true;
private T cachedValue = null;
private boolean updating = false;
private ValueUpdater updater = null;
/**
* Constructs a new instance bound to the given
* <code>ISWTObservableValue</code> and configured to fire change events
* once there have been no value changes in the observable for
* <code>delay</code> milliseconds.
*
* @param delayMillis
* @param observable
* @throws IllegalArgumentException
* if <code>updateEventType</code> is an incorrect type.
*/
public DelayedObservableValue(int delayMillis, IObservableValue<T> observable) {
super(observable.getRealm());
this.delay = delayMillis;
this.observable = observable;
observable.addValueChangeListener(this);
observable.addStaleListener(this);
cachedValue = doGetValue();
}
@Override
public void handleValueChange(ValueChangeEvent<? extends T> event) {
if (!updating)
makeDirty();
}
@Override
public void handleStale(StaleEvent staleEvent) {
if (!updating)
fireStale();
}
@Override
protected T doGetValue() {
if (dirty) {
cachedValue = observable.getValue();
dirty = false;
if (updater != null && !updater.running) {
fireValueChange(Diffs.createValueDiff(updater.oldValue,
cachedValue));
cancelScheduledUpdate();
}
}
return cachedValue;
}
@Override
protected void doSetValue(T value) {
updating = true;
try {
// Principle of least surprise: setValue overrides any pending
// update from observable.
dirty = false;
cancelScheduledUpdate();
T oldValue = cachedValue;
observable.setValue(value);
// Bug 215297 - target observable could veto or override value
// passed to setValue(). Make sure we cache whatever is set.
cachedValue = observable.getValue();
if (!Util.equals(oldValue, cachedValue))
fireValueChange(Diffs.createValueDiff(oldValue, cachedValue));
} finally {
updating = false;
}
}
@Override
public boolean isStale() {
ObservableTracker.getterCalled(this);
return (dirty && updater != null) || observable.isStale();
}
/**
* Returns the type of the value from {@link #doGetValue()}, i.e.
* String.class
*
* @see org.eclipse.core.databinding.observable.value.IObservableValue#getValueType()
*/
@Override
public Object getValueType() {
return observable.getValueType();
}
@Override
public synchronized void dispose() {
cancelScheduledUpdate();
if (observable != null) {
observable.dispose();
observable = null;
}
super.dispose();
}
private void makeDirty() {
if (!dirty) {
dirty = true;
fireStale();
}
cancelScheduledUpdate(); // if any
scheduleUpdate();
}
private void cancelScheduledUpdate() {
if (updater != null) {
updater.cancel();
updater = null;
}
}
private void scheduleUpdate() {
updater = new ValueUpdater(cachedValue);
getRealm().timerExec(delay, updater);
}
private void internalFireValueChange(final T oldValue) {
cancelScheduledUpdate();
fireValueChange(new ValueDiff<T>() {
@Override
public T getOldValue() {
return oldValue;
}
@Override
public T getNewValue() {
return getValue();
}
});
}
}
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