The TristatePort class is for use with GPIO pins that can be both input and output pins. It has nothing to do with tristate voltage levels in hardware.
A pin is considered "active" when it is an output pin. It is an input pin when it is in the "inactive" state. Your application can use the TristatePort class to control and monitor whether a particular GPIO pin is currently an input pin or an output pin.
Note that tristate ports can share pins with other tristate ports, for both reading and writing.
This class cannot be inherited.