Java tutorial
/******************************************************************************* * Copyright (c) 2000, 2011 IBM Corporation 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: * 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. * <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> * * 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 */ @Override public String toString() { String string = super.toString(); return string.substring(0, string.length() - 1) // remove trailing '}' + " detail=" + detail + "}"; } }