Focus Management

Gadget holders manage the keyboard focus. For a gadget, having the focus means that it can receive a keyboard event. A gadget has the focus when the user clicks on it with the mouse.

Pressing the Tab key moves the focus to the next gadget. Pressing Shift-Tab moves it to the previous gadget. By default, the Tab key moves from one gadget to another first from left to right, then from top to bottom. However, you can specify the order in which the gadgets are given the focus when the Tab key is pressed by defining a focus chain.

This section explains the following:

• Defining a Focus Chain

• Setting a Focus Chain Between Gadget Holders

• Notifying a Change of Focus

Defining a Focus Chain

Only the gadgets stored in the same gadget holder can be linked by a focus chain. To define a focus chain, use the following member functions of the IlvGraphic class:

• setNextFocusGraphic

• setPreviousFocusGraphic

• setLastFocusGraphic

• setFirstFocusGraphic

The name parameter provided in the member functions setNextFocusGraphic and setPreviousFocusGraphic is a symbolic name that must be created from the name of the target gadget. For example, if you want the next object in the focus chain of gadget to be the gadget named “Button”, call:

gadget->setNextFocusGraphic(IlvGetSymbol("Button"));

Setting a Focus Chain Between Gadget Holders

By default, the focus loops back to the first gadget in the chain when the user reaches the last gadget in the focus chain. You can, however, force the focus to another gadget holder that you specify using the following member functions:

• getNextFocusHolder

• setNextFocusHolder

• getPreviousFocusHolder

Notifying a Change of Focus

When the keyboard focus enters or leaves an IlvGadget object, its associated gadget holder generates the IlvKeyboardFocusIn and IlvKeyboardFocusOut events. These events are sent to the gadget, or to its associated interactor, if any, and are processed by the handleEvent member function. Then, the virtual member functions focusIn and focusOut are called. By default these member functions invoke the Focus In and Focus Out callbacks, respectively. See Associating a Callback with a Gadget.