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Java > Open Source Codes > org > eclipse > swt > events > TraverseEvent


1 /*******************************************************************************
2  * Copyright (c) 2000, 2006 IBM Corporation and others.
3  * All rights reserved. This program and the accompanying materials
4  * are made available under the terms of the Eclipse Public License v1.0
5  * which accompanies this distribution, and is available at
6  * http://www.eclipse.org/legal/epl-v10.html
7  *
8  * Contributors:
9  * IBM Corporation - initial API and implementation
10  *******************************************************************************/
11 package org.eclipse.swt.events;
12
13
14 import org.eclipse.swt.widgets.*;
15
16 /**
17  * Instances of this class are sent as a result of
18  * widget traversal actions.
19  * <p>
20  * The traversal event allows fine control over keyboard traversal
21  * in a control both to implement traversal and override the default
22  * traversal behavior defined by the system. This is achieved using
23  * two fields, <code>detail</code> and <code>doit</code>.
24  * </p><p>
25  * When a control is traversed, a traverse event is sent. The detail
26  * describes the type of traversal and the doit field indicates the default
27  * behavior of the system. For example, when a right arrow key is pressed
28  * in a text control, the detail field is <code>TRAVERSE_ARROW_NEXT</code>
29  * and the doit field is <code>false</code>, indicating that the system
30  * will not traverse to the next tab item and the arrow key will be
31  * delivered to the text control. If the same key is pressed in a radio
32  * button, the doit field will be <code>true</code>, indicating that
33  * traversal is to proceed to the next tab item, possibly another radio
34  * button in the group and that the arrow key is not to be delivered
35  * to the radio button.
36  * </p><p>
37  * How can the traversal event be used to implement traversal?
38  * When a tab key is pressed in a canvas, the detail field will be
39  * <code>TRAVERSE_TAB_NEXT</code> and the doit field will be
40  * <code>false</code>. The default behavior of the system is to
41  * provide no traversal for canvas controls. This means that by
42  * default in a canvas, a key listener will see every key that the
43  * user types, including traversal keys. To understand why this
44  * is so, it is important to understand that only the widget implementor
45  * can decide which traversal is appropriate for the widget. Returning
46  * to the <code>TRAVERSE_TAB_NEXT</code> example, a text widget implemented
47  * by a canvas would typically want to use the tab key to insert a
48  * tab character into the widget. A list widget implementation, on the
49  * other hand, would like the system default traversal behavior. Using
50  * only the doit flag, both implementations are possible. The text widget
51  * implementor sets doit to <code>false</code>, ensuring that the system
52  * will not traverse and that the tab key will be delivered to key listeners.
53  * The list widget implementor sets doit to <code>true</code>, indicating
54  * that the system should perform tab traversal and that the key should not
55  * be delivered to the list widget.
56  * </p><p>
57  * How can the traversal event be used to override system traversal?
58  * When the return key is pressed in a single line text control, the
59  * detail field is <code>TRAVERSE_RETURN</code> and the doit field
60  * is <code>true</code>. This means that the return key will be processed
61  * by the default button, not the text widget. If the text widget has
62  * a default selection listener, it will not run because the return key
63  * will be processed by the default button. Imagine that the text control
64  * is being used as an in-place editor and return is used to dispose the
65  * widget. Setting doit to <code>false</code> will stop the system from
66  * activating the default button but the key will be delivered to the text
67  * control, running the key and selection listeners for the text. How
68  * can <code>TRAVERSE_RETURN</code> be implemented so that the default button
69  * will not be activated and the text widget will not see the return key?
70  * This is achieved by setting doit to <code>true</code>, and the detail
71  * to <code>TRAVERSE_NONE</code>.
72  * </p><p>
73  * Note: A widget implementor will typically implement traversal using
74  * only the doit flag to either enable or disable system traversal.
75  * </p>
76  *
77  * @see TraverseListener
78  */
79
80 public final class TraverseEvent extends KeyEvent {
81     
82     /**
83      * The traversal type.
84      * <p><ul>
85      * <li>{@link org.eclipse.swt.SWT#TRAVERSE_NONE}</li>
86      * <li>{@link org.eclipse.swt.SWT#TRAVERSE_ESCAPE}</li>
87      * <li>{@link org.eclipse.swt.SWT#TRAVERSE_RETURN}</li>
88      * <li>{@link org.eclipse.swt.SWT#TRAVERSE_TAB_NEXT}</li>
89      * <li>{@link org.eclipse.swt.SWT#TRAVERSE_TAB_PREVIOUS}</li>
90      * <li>{@link org.eclipse.swt.SWT#TRAVERSE_ARROW_NEXT}</li>
91      * <li>{@link org.eclipse.swt.SWT#TRAVERSE_ARROW_PREVIOUS}</li>
92      * <li>{@link org.eclipse.swt.SWT#TRAVERSE_MNEMONIC}</li>
93      * <li>{@link org.eclipse.swt.SWT#TRAVERSE_PAGE_NEXT}</li>
94      * <li>{@link org.eclipse.swt.SWT#TRAVERSE_PAGE_PREVIOUS}</li>
95      * </ul></p>
96      *
97      * Setting this field will change the type of traversal.
98      * For example, setting the detail to <code>TRAVERSE_NONE</code>
99      * causes no traversal action to be taken.
100      *
101      * When used in conjunction with the <code>doit</code> field, the
102      * traversal detail field can be useful when overriding the default
103      * traversal mechanism for a control. For example, setting the doit
104      * field to <code>false</code> will cancel the operation and allow
105      * the traversal key stroke to be delivered to the control. Setting
106      * the doit field to <code>true</code> indicates that the traversal
107      * described by the detail field is to be performed.
108      */
109     public int detail;
110     
111     static final long serialVersionUID = 3257565105301239349L;
112     
113 /**
114  * Constructs a new instance of this class based on the
115  * information in the given untyped event.
116  *
117  * @param e the untyped event containing the information
118  */
119 public TraverseEvent(Event e) {
120     super(e);
121     this.detail = e.detail;
122 }
123
124 /**
125  * Returns a string containing a concise, human-readable
126  * description of the receiver.
127  *
128  * @return a string representation of the event
129  */
130 public String JavaDoc toString() {
131     String JavaDoc string = super.toString ();
132     return string.substring (0, string.length() - 1) // remove trailing '}'
133 + " detail=" + detail
134         + "}";
135 }
136 }
137
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