- All Implemented Interfaces:
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
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
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
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
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
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
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
Note: A widget implementor will typically implement traversal using only the doit flag to either enable or disable system traversal.
detailpublic 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.
(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