+ * 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. + *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
+ + "}";
+}
+}