How could I know the User switched back to my WatchFace?thanks.

I am not good at English and I am trying to ask a question. Thanks a lot for your answer.

I need to know the user just back to my watchface from other actions like from running or something else. Then I can do something like : if (backToMyWatchFace == true) { drawtext(x,y,font,   "nice to see you again",color}.

I don't know how to get it.

If you get any ideas, please let me know. Thanks.