Question

I currently have a viewpageindicator with three tab 1,2 and 3.
The problem is when i swipe to tab 2, the onActivityCreated from fragment 3 is being called.

At my tab 3 fragment, i will call a asyntask onActivityCreated , therefore when fragment 2 is being switched, it will load a asyntask.

Answer 1

By default, ViewPagers load one Fragment on either side of the current Fragment. To know when a Fragment is in the centre, you could use the onPageChangeListener of the ViewPager in combination with an interface implemented by every Fragment subclass.

public interface FragmentChangeListener
{
void onCentered();
}

Implement this interface in every Fragment

public class CustomFragment extends Fragment implements FragmentChangeListener
{
....
 @Override
 public void onCentered()
 {
 //Show alertDialog and start asyncTask
 }
}

In your Activity class:

ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener()
{
  @Override
  public void onPageSelected(int position)
  {
    FragmentChangeListener listener = (FragmentChangeListener) //cast fragment at this position to FragmentChangeListener
    listener.onCentered();
  }
}