bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/events/TraverseEvent.java

/*******************************************************************************
 * Copyright (c) 2000, 2011 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.swt.events;


import org.eclipse.swt.widgets.*;

/**
 * Instances of this class are sent as a result of
 * widget traversal actions.
 * <p>
 * The traversal event allows fine control over keyboard traversal
 * in a control both to implement traversal and override the default
 * traversal behavior defined by the system.  This is achieved using
 * two fields, <code>detail</code> and <code>doit</code>.
 * </p><p>
 * When a control is traversed, a traverse event is sent.  The detail
 * describes the type of traversal and the doit field indicates the default
 * behavior of the system.  For example, when a right arrow key is pressed
 * in a text control, the detail field is <code>TRAVERSE_ARROW_NEXT</code>
 * and the doit field is <code>false</code>, indicating that the system
 * will not traverse to the next tab item and the arrow key will be
 * delivered to the text control.  If the same key is pressed in a radio
 * button, the doit field will be <code>true</code>, indicating that
 * traversal is to proceed to the next tab item, possibly another radio
 * button in the group and that the arrow key is not to be delivered
 * to the radio button.
 * </p><p>
 * How can the traversal event be used to implement traversal?
 * When a tab key is pressed in a canvas, the detail field will be
 * <code>TRAVERSE_TAB_NEXT</code> and the doit field will be
 * <code>false</code>.  The default behavior of the system is to
 * provide no traversal for canvas controls.  This means that by
 * default in a canvas, a key listener will see every key that the
 * user types, including traversal keys.  To understand why this
 * is so, it is important to understand that only the widget implementor
 * can decide which traversal is appropriate for the widget.  Returning
 * to the <code>TRAVERSE_TAB_NEXT</code> example, a text widget implemented
 * by a canvas would typically want to use the tab key to insert a
 * tab character into the widget.  A list widget implementation, on the
 * other hand, would like the system default traversal behavior.  Using
 * only the doit flag, both implementations are possible.  The text widget
 * implementor sets doit to <code>false</code>, ensuring that the system
 * will not traverse and that the tab key will be delivered to key listeners.
 * The list widget implementor sets doit to <code>true</code>, indicating
 * that the system should perform tab traversal and that the key should not
 * be delivered to the list widget.
 * </p><p>
 * How can the traversal event be used to override system traversal?
 * When the return key is pressed in a single line text control, the
 * detail field is <code>TRAVERSE_RETURN</code> and the doit field
 * is <code>true</code>.  This means that the return key will be processed
 * by the default button, not the text widget.  If the text widget has
 * a default selection listener, it will not run because the return key
 * will be processed by the default button.  Imagine that the text control
 * is being used as an in-place editor and return is used to dispose the
 * widget.  Setting doit to <code>false</code> will stop the system from
 * activating the default button but the key will be delivered to the text
 * control, running the key and selection listeners for the text.  How
 * can <code>TRAVERSE_RETURN</code> be implemented so that the default button
 * will not be activated and the text widget will not see the return key?
 * This is achieved by setting doit to <code>true</code>, and the detail
 * to <code>TRAVERSE_NONE</code>.
 * </p><p>
 * Note: A widget implementor will typically implement traversal using
 * only the doit flag to either enable or disable system traversal.
 * </p>
 * 
 * @see TraverseListener
 * @see <a href="http://www.eclipse.org/swt/">Sample code and further information</a>
 */

public final class TraverseEvent extends KeyEvent {
	
	/**
	 * The traversal type.
	 * <p><ul>
	 * <li>{@link org.eclipse.swt.SWT#TRAVERSE_NONE}</li>
	 * <li>{@link org.eclipse.swt.SWT#TRAVERSE_ESCAPE}</li>
	 * <li>{@link org.eclipse.swt.SWT#TRAVERSE_RETURN}</li>
	 * <li>{@link org.eclipse.swt.SWT#TRAVERSE_TAB_NEXT}</li>
	 * <li>{@link org.eclipse.swt.SWT#TRAVERSE_TAB_PREVIOUS}</li>
	 * <li>{@link org.eclipse.swt.SWT#TRAVERSE_ARROW_NEXT}</li>
	 * <li>{@link org.eclipse.swt.SWT#TRAVERSE_ARROW_PREVIOUS}</li>
	 * <li>{@link org.eclipse.swt.SWT#TRAVERSE_MNEMONIC}</li>
	 * <li>{@link org.eclipse.swt.SWT#TRAVERSE_PAGE_NEXT}</li>
	 * <li>{@link org.eclipse.swt.SWT#TRAVERSE_PAGE_PREVIOUS}</li>
	 * </ul></p>
	 * 
	 * Setting this field will change the type of traversal.
	 * For example, setting the detail to <code>TRAVERSE_NONE</code>
	 * causes no traversal action to be taken.
	 * 
	 * When used in conjunction with the <code>doit</code> field, the
	 * traversal detail field can be useful when overriding the default
	 * traversal mechanism for a control. For example, setting the doit
	 * field to <code>false</code> will cancel the operation and allow
	 * the traversal key stroke to be delivered to the control. Setting
	 * the doit field to <code>true</code> indicates that the traversal
	 * described by the detail field is to be performed.
	 */
	public int detail;
	
	static final long serialVersionUID = 3257565105301239349L;
	
/**
 * Constructs a new instance of this class based on the
 * information in the given untyped event.
 *
 * @param e the untyped event containing the information
 */
public TraverseEvent(Event e) {
	super(e);
	this.detail = e.detail;
}

/**
 * Returns a string containing a concise, human-readable
 * description of the receiver.
 *
 * @return a string representation of the event
 */
public String toString() {
	String string = super.toString ();
	return string.substring (0, string.length() - 1) // remove trailing '}'
		+ " detail=" + detail
		+ "}";
}
}