HI,
Ok here is an option to do
1. Create a List in SP that stores a users email, their Display name, and LastPingedDateTime
2. Add a Timer to your app
3. Set the timer to run like every 1-5 minutes
now in the TImer, when it triggers you would update the LastPingedDateTime for that user who is logge din
4. Add a Screen that shows everyone who has updated the LastPingDateTime, WITHIN the Timer time.
So if you ping every 5 minutes, then you would show everyone who has pinged within the last 5 minutes.
Then you could have another timer (or use the same one) to Refresh the Gallery
So as soon as a persons time is past 5 minutes they would drop off.
Now you are showing everyone that is FOR SURE logged in, but you have some delay of up to 5 minutes before someone falls off who exitted the app.
If this answers your quesiton please mark as the answer.