onPageSelected isn't triggered when calling setCurrentItem(0)

Question

I have an Activity with a ViewPager which displays a bunch of pictures. When it starts the ViewPager\'s position is set based on what the user selected in a previous Activit

Answer 1

The following solution seems to work for me. i.e. I get a callback at position 0 when the viewpager is first loaded and for all subsequent selections either from user scrolling or a setCurrentItem(x) call. I haven't observed any undesired behaviour.

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

                if (positionOffsetPixels == 0) {
                 //Do something on selected page at position
                }

            }

            @Override
            public void onPageSelected(int position) {}

            @Override
            public void onPageScrollStateChanged(int state) {}
        });

Answer 2

The simplest solution will be using of function e.g.

    viewpager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {

        @Override
        public void onPageScrollStateChanged(int state) {}

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {}

        @Override
        public void onPageSelected(int position) {
            onPage(position);
        }
    });

    // call first time
    onPage(0); 

    private void onPage(int position) {
        //...
    }

Answer 3

if you don't care screen animotion try

pager.setCurrentItem(1);
pager.setCurrentItem(0);

Answer 4

onPageSelected is not triggered for page which is opened first. For this case I manually perform all needed actions. Also, I suppose that call to onPageSelected(0) should work too.

Answer 5

If the ViewPager is in a fragment, in the onViewCreated method, call mPager.setOnPageChangeListener(this)

Answer 6

The cleanest solution I've found to this so far is to take a reference to the onPageChangeListener you set on the ViewPager (since I don't think there's a ViewPager.getOnPageChangeListener() method), then after you've set the ViewPager's adapter, call:

onPageChangeListener.onPageSelected(viewPager.getCurrentItem());

However, the fragment for the page at the current index won't have been instantiated yet (at least if you're using FragmentStatePagerAdapter), so you may need to wrap it in a runnable, ala:

viewPager.post(new Runnable(){
@Override
    public void run() {
        onPageChangeListener.onPageSelected(viewPager.getCurrentItem());
    }
});

Also, if within the onPageSelected handler you need a reference to the fragment, you'll have to do that yourself. I use an abstract base class for my FragmentStatePagerAdapter which overrides the instantiate and destroy methods, and adds/removes the fragments from a SparseArray.