Ok, now I understand. If you are interested in the eye tracker connection you need to pass TX_STATEPATH_EYETRACKINGSTATE in the call to txRegisterStateChangedHandler (row 8 in the second code snippet in post #2020)
Then, in the switch statement you can choose to handle the device status value you are interested in, one or many of these:
TX_EYETRACKINGDEVICESTATUS_INITIALIZING,
TX_EYETRACKINGDEVICESTATUS_NOTAVAILABLE,
TX_EYETRACKINGDEVICESTATUS_INVALIDCONFIGURATION,
TX_EYETRACKINGDEVICESTATUS_DEVICENOTCONNECTED,
TX_EYETRACKINGDEVICESTATUS_TRACKING,
TX_EYETRACKINGDEVICESTATUS_TRACKINGPAUSED,
TX_EYETRACKINGDEVICESTATUS_CONFIGURING,
TX_EYETRACKINGDEVICESTATUS_UNKNOWNERROR,
TX_EYETRACKINGDEVICESTATUS_CONNECTIONERROR
See the header documentation in EyeXFrameworkTypes.h to learn more about what each enum value mean.