Java tutorial
/******************************************************************************* * Copyright (c) 2008, 2012 Innoopract Informationssysteme GmbH 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: * Innoopract Informationssysteme GmbH - initial API and implementation * EclipseSource - ongoing development ******************************************************************************/ package org.eclipse.swt.events; import org.eclipse.swt.widgets.Event; /** * 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 * * @since 1.2 */ public final class TraverseEvent extends KeyEvent { private static final long serialVersionUID = 1L; /** * 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. */ @SuppressWarnings("javadoc") public int detail; /** * 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); detail = e.detail; } /** * Returns a string containing a concise, human-readable description of the * receiver. * * @return a string representation of the event */ @Override public String toString() { String string = super.toString(); return string.substring(0, string.length() - 1) // remove trailing '}' + " detail=" + detail + "}"; } }