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/*******************************************************************************
* 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.
*
* 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, detail and doit.
*
* 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 TRAVERSE_ARROW_NEXT
* and the doit field is false, 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 true, 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.
*
* How can the traversal event be used to implement traversal?
* When a tab key is pressed in a canvas, the detail field will be
* TRAVERSE_TAB_NEXT and the doit field will be
* false. 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 TRAVERSE_TAB_NEXT 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 false, 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 true, indicating
* that the system should perform tab traversal and that the key should not
* be delivered to the list widget.
*
* 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 TRAVERSE_RETURN and the doit field
* is true. 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 false 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 TRAVERSE_RETURN 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 true, and the detail
* to TRAVERSE_NONE.
*
* Note: A widget implementor will typically implement traversal using
* only the doit flag to either enable or disable system traversal.
*
*
* @see TraverseListener
* @see Sample code and further information
*/
public final class TraverseEvent extends KeyEvent {
/**
* The traversal type.
*
* - {@link org.eclipse.swt.SWT#TRAVERSE_NONE}
* - {@link org.eclipse.swt.SWT#TRAVERSE_ESCAPE}
* - {@link org.eclipse.swt.SWT#TRAVERSE_RETURN}
* - {@link org.eclipse.swt.SWT#TRAVERSE_TAB_NEXT}
* - {@link org.eclipse.swt.SWT#TRAVERSE_TAB_PREVIOUS}
* - {@link org.eclipse.swt.SWT#TRAVERSE_ARROW_NEXT}
* - {@link org.eclipse.swt.SWT#TRAVERSE_ARROW_PREVIOUS}
* - {@link org.eclipse.swt.SWT#TRAVERSE_MNEMONIC}
* - {@link org.eclipse.swt.SWT#TRAVERSE_PAGE_NEXT}
* - {@link org.eclipse.swt.SWT#TRAVERSE_PAGE_PREVIOUS}
*
*
* Setting this field will change the type of traversal.
* For example, setting the detail to TRAVERSE_NONE
* causes no traversal action to be taken.
*
* When used in conjunction with the doit field, the
* traversal detail field can be useful when overriding the default
* traversal mechanism for a control. For example, setting the doit
* field to false will cancel the operation and allow
* the traversal key stroke to be delivered to the control. Setting
* the doit field to true 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
+ "}";
}
}