Android : How to add elements to Viewpager dynamically android

I'm using viewpager to swipe between view.Initially i'm loading 5 items to viewpager.When scrolling 5th page i'm downloading remaining 20 elements from server.How to acheive that.I have enable notifyDatasetChanged().It is also not working.

I have tried viewpager.setAdapter(adapter).It is working but it's scrolls to the 0th position.

How to acheive this?

Thanks in adavance:)