public final class TraverseEvent extends KeyEventInstances 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,
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_NEXTand 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_NEXTand 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_NEXTexample, 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_RETURNand 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
falsewill 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_RETURNbe 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
Note: A widget implementor will typically implement traversal using only the doit flag to either enable or disable system traversal.
- See Also:
All Methods Instance Methods Concrete Methods Modifier and Type Method Description
toString()Returns a string containing a concise, human-readable description of the receiver.
public int detailThe traversal type.
TRAVERSE_NONEcauses no traversal action to be taken. When used in conjunction with the
doitfield, the traversal detail field can be useful when overriding the default traversal mechanism for a control. For example, setting the doit field to
falsewill cancel the operation and allow the traversal key stroke to be delivered to the control. Setting the doit field to
trueindicates that the traversal described by the detail field is to be performed.
public TraverseEvent(Event e)Constructs a new instance of this class based on the information in the given untyped event.
e- the untyped event containing the information