/*******************************************************************************
* 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
*******************************************************************************/
package org.eclipse.jface.internal.databinding.provisional.swt;
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.ObservableTracker;
import org.eclipse.swt.events.DisposeEvent;
import org.eclipse.swt.events.DisposeListener;
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.widgets.Control;
/**
* NON-API - A ControlUpdater updates an SWT control in response to changes in the model.
* By wrapping a block of code in a ControlUpdater, clients can rely on the fact
* that the block of code will be re-executed whenever anything changes in the
* model that might affect its behavior.
*
* <p>
* ControlUpdaters only execute when their controls are visible. If something changes
* in the model while the control is invisible, the updator is flagged as dirty and
* the updator stops listening to the model until the next time the control repaints.
* This saves CPU cycles by deferring UI updates to widgets that are currently invisible.
* </p>
*
* <p>
* Clients should subclass this when copying information from the model to
* a control. Typical usage:
* </p>
*
* <ul>
* <li>Override updateControl. It should do whatever is necessary to display
* the contents of the model in the control.</li>
* <li>In the constructor, attach listeners to the model. The listeners should
* call markDirty whenever anything changes in the model that affects
* updateControl. Note: this step can be omitted when calling any method
* tagged with "@TrackedGetter" since ControlUpdater will automatically attach
* a listener to any object if a "@TrackedGetter" method is called in
* updateControl.</li>
* <li>(optional)Extend dispose() to remove any listeners attached in the constructor</li>
* </ul>
*
* <p>
* Example:
* </p>
*
* <code>
* // Displays an observable value in a label and keeps the label in synch with changes
* // in the value.
* IReadableValue someValue = ...
* final Label myLabel = new Label(parent, SWT.NONE);
* new ControlUpdater(myLabel) {
* protected void updateControl() {
* myLabel.setText(someValue.getValue().toString);
* }
* }
* // myLabel will display the value of someValue the next time it repaints, and will automatically
* // be updated whenever someValue changes and the label is visible
* </code>
*
* @since 1.1
*/
public abstract class ControlUpdater {
private class PrivateInterface implements PaintListener,
DisposeListener, Runnable, IChangeListener {
// PaintListener implementation
public void paintControl(PaintEvent e) {
updateIfNecessary();
}
// DisposeListener implementation
public void widgetDisposed(DisposeEvent e) {
ControlUpdater.this.dispose();
}
// Runnable implementation. This method runs at most once per repaint whenever the
// value gets marked as dirty.
public void run() {
if (theControl != null && !theControl.isDisposed() && theControl.isVisible()) {
updateIfNecessary();
}
}
// IChangeListener implementation (listening to the ComputedValue)
public void handleChange(ChangeEvent event) {
// Whenever this updator becomes dirty, schedule the run() method
makeDirty();
}
}
private Runnable updateRunnable = new Runnable() {
public void run() {
updateControl();
}
};
private PrivateInterface privateInterface = new PrivateInterface();
private Control theControl;
private IObservable[] dependencies = new IObservable[0];
private boolean dirty = false;
/**
* Creates an updator for the given control.
*
* @param toUpdate control to update
*/
public ControlUpdater(Control toUpdate) {
theControl = toUpdate;
theControl.addDisposeListener(privateInterface);
theControl.addPaintListener(privateInterface);
makeDirty();
}
private void updateIfNecessary() {
if (dirty) {
dependencies = ObservableTracker.runAndMonitor(updateRunnable, privateInterface, null);
dirty = false;
}
}
/**
* This is called automatically when the control is disposed. It may also
* be called explicitly to remove this updator from the control. Subclasses
* will normally extend this method to detach any listeners they attached
* in their constructor.
*/
public void dispose() {
theControl.removeDisposeListener(privateInterface);
theControl.removePaintListener(privateInterface);
stopListening();
}
private void stopListening() {
// Stop listening for dependency changes
for (int i = 0; i < dependencies.length; i++) {
IObservable observable = dependencies[i];
observable.removeChangeListener(privateInterface);
}
}
/**
* Updates the control. This method will be invoked once after the
* updator is created, and once before any repaint during which the
* control is visible and dirty.
*
* <p>
* Subclasses should overload this method to provide any code that
* changes the appearance of the widget.
* </p>
*/
protected abstract void updateControl();
/**
* Marks this updator as dirty. Causes the updateControl method to
* be invoked before the next time the control is repainted.
*/
protected final void makeDirty() {
if (!dirty) {
dirty = true;
stopListening();
SWTUtil.runOnce(theControl.getDisplay(), privateInterface);
}
}
}