Ideal way of updating app's views when data changes

Okay this is not platform specific question. But any answer related to iOS,Android or Windows Phone will help. So I am building a chat application (yes another one) but I am really confused about how you pros handle GUI update when a chat message arrives. I am not really concerned about performance issues but how devs update various part of app's GUI showing updated data.

For example Whatsapp has one master list where all the open chats are listed and then a separate chat display window(activity in case of Androids).

So when some message arrives, how do they update both views at the same time? Like if I am already chatting with someone and I receive a new message, the list gets updated as soon as the message arrives. I get this part but how is master list updated. Are they constructing whole of master view again after each and every single message? I just wanted to know the ideal mechanism to deal with this scenario.