How Silverlight implements tab sequence concepts
The Silverlight programming model defines a Control class that is a base class of many of the practical controls that produce a Silverlight application user interface. One of the behaviors of the Control class is that only a Control can receive keyboard focus as a discrete element within the Silverlight content area.
When a Silverlight application user interface is constructed from the visual tree, a default tab sequence for all Silverlight content is also constructed, using the same principles of order that were used by the visible layout. This default tab sequence is usually adequate as a tab sequence that supports users that press the TAB key to traverse the UI. The same TAB sequence and/or the focusable state of controls is also used by many assistive technologies or modes of assistive technologies to construct the representation of the interface for the Silverlight content.
For cases where developers decide that the default tab sequence is not adequate, the developer can take one of two approaches for changing the tab sequence:
- Change other properties of the control where a change to the tab sequence happens as a secondary effect.
- Reorder the tab sequence directly.
Changing control properties
- Setting the Visibility property of a control to Collapsed causes the control to no longer render in the UI. As a secondary effect, that control is removed from the tab sequence.
- Setting the IsEnabled property of a control to false causes the control to no longer be focusable by keyboard or clickable by the mouse. In many cases, the visual appearance of the control changes also, through a theme style. For example, the control may appear as gray rather than black. As a secondary effect, that control is removed from the tab sequence.
Changing specific tab properties
- Setting the IsTabStop property of a control to false causes the control to no longer be focusable by keyboard or programmatic focus, and that control is removed from the tab sequence.
- Setting the TabIndex property of a control to a specific index causes the control to be inserted at that position in the tab sequence. The default value of TabIndex is Single.MaxValue, therefore any non-default value promotes that control to be first in an otherwise default tab sequence. More typically, authors would specify a TabIndex for any controls that are involved in a deliberate segment of tab order re-ordering.
Tab order and language
Left-to-right is the default only for languages that use left-to-right reading order. For languages that use right-to-left reading order, right-to-left is also the default tab order as implemented by Silverlight runtime behavior. That language preference is declared by the acting CultureInfo.