delite/KeyNav

This is a base class to enable keyboard navigation between the widget's descendants. Navigation can be performed via arrow keys and HOME/END keys, and also a letter key search. A List, Tree, or Grid widget could all be subclasses of KeyNav.

Keystroke Handlers

To use this base class, the subclass should implement methods for the keystrokes that it wants to handle. For LEFT/RIGHT/UP/DOWN arrow key navigation, implement:

• previousKeyHandler(event, currentDescendant)
• nextKeyHandler(event, currentDescendant)
• downKeyHandler(event, currentDescendant)
• upKeyHandler(event, currentDescendant)

The subclass can implement methods for other keys too, following the naming pattern above, for example spaceKeyHandler(), f2KeyHandler(), etc.

If a handler is defined, then KeyNav automatically calls evt.preventDefault() and evt.stopPropagation().

Other Requirements

In addition to setting up keystroke handler methods, the subclass must:

• Set all descendants' initial tabIndex to "-1"; both initial descendants and any descendants added later, by for example addChild(). Exception: if focusDescendants is false then the descendants shouldn't have any tabIndex at all.
• Define descendantSelector as a function (descendantSelector(Element)) or CSS selector (ex: ".list-item") that identifies navigable descendant widgets.
• Define this.containerNode.

Also, child widgets must implement a .focus() method.

Example