ViewPager - onCreateView is not always called

Question

I have a ViewPager with 10 pages. When I start the last (10th) page onCreateView() method of my fragment is called. When I swipe to the 9th page onCreateView() is called also. But when I back to the 10th page onCreateView() isn't called. What's wrong?

Teletypesetter

Post the code for we understanding what is going on – Exceedingly

Your ViewPager adapter may cause this problem. But i cannot know without seeing your code... – Sweptwing

Any proper solution for this issue? – Spank

Answer 1

Try Extending FragmentStatePagerAdapter

Rodriquez

It should be accepted Answer, it works Perfect for me. Thanks. :) – Rescissory

Yes, it works and it really should be the accepted answer. – Engraving

@MehrdadSComputer The fragment is recreated when page is selected. so onCreateView is called – Rodriquez

@Rodriquez when we extend FragmentPagerAdapter, the same won't happen? – Holloweyed

@MehrdadSComputer Yes. the fragment is saved when FragmentPagerAdapter is used . when the user returns to previous fragment it is displayed taking from memory instead of re-creating the fragment. – Rodriquez

Answer 2

That is because a FragmentPagerAdapter keeps in memory every fragment. Hence, when you visit the first time the fragment, onCreate will be invoked but the second time Android will looking for in memory, so it not need invoke onCreate.

If you need run the code in OnCreate every time fragment is displayed, you should move it to getItem(int id)

See offical documentation: http://developer.android.com/reference/android/support/v4/app/FragmentPagerAdapter.html

Mohandis

Thank you, but I added Log.i("hello", "hello" + id); to getItem method, and this log I only see when I start the viewpager. When I swipe between pages it doesn't invoke. – Teletypesetter

Ok, try to override onResume method. – Mohandis

onResume for Fragment or FragmentPagerAdapter ? – Teletypesetter

onResume for Fragment, or if you need call that code in OnCreate and in OnResume, you can write a separate function and invoke it from that two methods. – Mohandis

Answer 3

Nothing is wrong. The ViewPager already has the page, and so it does not need to create it.

Ultimogeniture

How can I do it when any of method (onStart, OnCreate, onCreateView) isn't inoke? – Teletypesetter

@Bakus123: One possibility is to add an OnPageChangeListener to the ViewPager, so you know when it changes pages. Or, just update the page when the data changes, rather than waiting for the user to swipe to it, for all pages that have been created so far. – Ultimogeniture

@Bakus123: You will need to keep track of which fragments exist and belong to which positions. Then, you can call some method on your fragments to tell them to update based upon the page change. – Ultimogeniture

Answer 4

I had the same problem, my solution was to assign again the adapter of the ViewPager instance, just like:

pager.setAdapter(adapter);

This causes a restart of the "mItems" property from the viewPager and removes the cache.

But I don't know if it's a safe solution

Laky

Answer 5

You can call the adapter getItem from onPageSelect, which is called also on swipes, and place your code inside the getItem, or even in the onPageSeelect itself.

Heterocercal

Answer 6

CommonWare's answer is the best and works like charm: simple add OnPageChangeListener to your ViewPager item, something like this:

ViewPager     viewPager    = null;
PagerAdapter  pagerAdapter = null;

//Some code come here...

pagerAdapter = new PagerAdapter(); //Or any class derived from it
viewPager    = (ViewPager)findViewById(R.id.container);//Connect it to XML
viewPager.setAdapter (mPagerAdapter); //Connect the two

//Next two lines are simply for fun...
//viewager.setPageTransformer(true, new DepthPageTransformer());
//viewPager.setPageTransformer(true, new PaymentZoomOutPageTransformer());

 viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }
        //This is the right place to connect the pages with a data struct!!!
        @Override
        public void onPageSelected(int position) {
            // Here you can connect the current displayed page with some data..
        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });

 //Here use the inflater to add views/pages
 //Don't forget to do:
 pagerAdapter.notifyDataSetChanged();
 //When you're done...

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