This means that the host will call the UI's port_event() function when
the port value changes (as defined by protocol).
Calling this function with the same port_index and port_protocol
as an already active subscription has no effect.
@param handle The handle field of this struct.
@param port_index The index of the port.
@param port_protocol The URID of the ui:PortProtocol.
@param features Features for this subscription.
@return 0 on success.
Subscribe to updates for a port.
This means that the host will call the UI's port_event() function when the port value changes (as defined by protocol).
Calling this function with the same port_index and port_protocol as an already active subscription has no effect.
@param handle The handle field of this struct. @param port_index The index of the port. @param port_protocol The URID of the ui:PortProtocol. @param features Features for this subscription. @return 0 on success.