Detecting if widget is visible on the screen (for lazy loading)

[kimusan]

Hi,
I have some verticalScroll that contains a large number (100+) widgets. Some of the widgets' content relies on some data it needs to fetch from the net so to not fetch all the data at once, I would like to implement some simple form of lazy loading such that the data is only fetch when the Vertical Scroll is showing the actual widget(s).
Is there a way to detect this easily without running through all of the widgets and identifying their individual locations on every scroll. With 100+ widgets it seems to slow down scrolling a lot.