FragmentPageAdapter works in a strange way

Question

Since in Android L the the Action bar navigation modes are deprecated I'm searching an other way to have the tab and I found that is possible to use the PagerTabStrip (android.support.v4.view.PagerTabStrip), so I created a FragmentPageAdapter in this way:

public class TitleAdapter extends FragmentPagerAdapter {

    private final String titles[] = new String[] { "Home", "Events", "People", "Books"};
    private final Fragment frags[] = new Fragment[titles.length];
    Context context;
    public TitleAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public CharSequence getPageTitle(int position) {
        Log.v("TitleAdapter - getPageTitle=", titles[position]);
        return titles[position];
    }

    @Override
    public Fragment getItem(int position) {
        Log.v("TitleAdapter - getItem=", String.valueOf(position));
        //return frags[position];
        switch (position) {
        case 0:
            return Home.newInstance(0, "Home");
        case 1:
            return Events.newInstance(1, "Events");
        case 2:
            return People.newInstance(2, "People");
        case 4:
            return Books.newInstance(3, "Books"); 
        }
        return null;
    }

    @Override
    public int getCount() {
        return frags.length;
    }
}

The strange way that i see in LogCat is that the method getItem() is called 4 times when the mainActivity starts so I've to wait a lots because in each Tab there is a quite long list and this list is populated via HTTP request calling a web service.

I wish load only a fragment each times and not all. When i used actionbar.Tablistener it was possible but now the method is deprecated so is there a way to do that?

I set the adapter and the viewPager in the onCreate method in this way:

@Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.prova_page_tab_stripes);
        mViewPager = (ViewPager) findViewById(R.id.viewpager);

        titleAdapter = new TitleAdapter(getSupportFragmentManager());
        mViewPager.setAdapter(titleAdapter);
        mViewPager.setOffscreenPageLimit(1);
    }

Answer 1

The number of pages initialized depends on setOffscreenPageLimit function of ViewPager. As per android doc in http://developer.android.com/reference/android/support/v4/view/ViewPager.html#setOffscreenPageLimit(int),

public void setOffscreenPageLimit (int limit)

Set the number of pages that should be retained to either side of the current page in the view hierarchy in an idle state. Pages beyond this limit will be recreated from the adapter when needed. This is offered as an optimization. If you know in advance the number of pages you will need to support or have lazy-loading mechanisms in place on your pages, tweaking this setting can have benefits in perceived smoothness of paging animations and interaction. If you have a small number of pages (3-4) that you can keep active all at once, less time will be spent in layout for newly created view subtrees as the user pages back and forth. You should keep this limit low, especially if your pages have complex layouts. This setting defaults to 1. Parameters limit How many pages will be kept offscreen in an idle state.

Set it to 1 or keep it to default if you wan to limit pages to be retained.

But if you want to load the data only in one page at a time, you can determine when fragment becomes visible and then load the data (insted of loading in onCreateView.) Refer this question: How to determine when Fragment becomes visible in ViewPager