ControlContext :: value - Get Value handle
The function returns value handle that acts as data source for the control.
In case of user-defined data sources, controls may (temporarily) not refer to a data source. When no data source is available for the control, the function throws an exception. In order to avoid exceptions, one may call hasData() before calling value() .
In case of combo-boxes, the value handle returns the value handle for the combo box data source.
Return value: Value handle ( odaba::Value & )
The value handle is a reference to an (usually) opened value. Invalid or not opened value handles my cause an exception.