I am having a requirement on just want to show/display the Skype for business user presence(Busy, Available, Off Work etc) in UWP app. I am able to display the user presence using UCWA rest APIs but want to subscribe the event which will tell me that the presence got changed, so that I can update it on UWP app also.
In UCWA documentation mentioned there is an event to subscribe it, UCWA Presence reference , presence is the event. but here I got stuck how to subscribe it in UWP app, can anyone please help me out on this?
This article provides a little more elaborated walkthrough: Subscribe to Contacts Presence
To reply your question: you need to understand and work with Event Channel, the article linked above goes through that too. You'll always need to have a thread listening on Event Channel (URL), and when (in your case) a subscribed contact will change status presence, that will come through Event Channel.
See also: Set up the UCWA event channel to receive incoming notifications
If you need it to have it lasting for potential long or 'persistent' presence subscription, then it's very important you understand also how to properly report activity for your UCWA app.
See also: me Dashboard
The only sample code that implements these concepts is
Lync 2013: Open an event channel in a UCWA app using C#/XAML and XML
So it is WinRT and not UWP, but if you're using C#/XAML it'll probably help.