Observer Design Pattern, Concrete Subject Can Expose getData()? [closed]

First-time Target switch on, In My Application, I want to show some data on List, I am Observing for DataUpdate on App, but my Service will push data for every 30sec if My app is up at 15sec, I don't have data to show(instead of showing not data found), can we design observer design pattern in such a way that it can expose getdata()(which contain lease recent data).

so While the app is up I will call getdata() then registerObserver().

Is this is a correct approach?