Class Cast Exception in instantiateItem of a ViewPager

Question

I want to set some TextViews in fragments inside of a ViewPager. i'm setting my TextViews in onActivityCreated function of my fragments when it's instantiate pages . according to some posts returning POSITION_NONE in getItemPosition solve my problem but because of deleting all views everytime it's not an efficient way.so i've change it to instatiateItem(ViewGroup container, int position) but when i returning the view of my Fragments it throws :

ClassCastException : android.Widget.LinearLayout cannot be cast to android.support.v4.app.Fragment

here is my instantiateItem(ViewGroup container, int position) function, does anybody know how can i manage this exception? or how can i refresh a TextView in a Fragment inside of a ViewPager? Thanks in Advance

@Override
    public Object instantiateItem(ViewGroup container, int position) 
    {
        LayoutInflater inflater = (LayoutInflater) mContext
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        if (position == 3) {
            view = inflater.inflate(R.layout.projecttracking_detail_customerproject_fragment, null);
            ((ViewPager) container).addView(view, 0);
        }
        else if(position == 2) {
            view = inflater.inflate(R.layout.projecttracking_detail_projectinformation_fragment, null);
            ((ViewPager) container).addView(view, 0);
        }


        return view;

    }

Answer 1

If you have a fragment based ViewPager then you can't override instantiateItem() to return a View as that returned object will be treated like a Fragment later(what the exception is telling you).

I don't fully understand what you want so, if you want to update some of the views(from all of the fragments?) from the fragments then you could use the POSITION_NONE option.

You could also just update the current stored fragments from the ViewPager and let the other query for data(in the onCreateView()) when they get recreated as the user swipes towards them. For a FragmentPagerAdapter you could use this to access the current stored visible fragments:

PageFragment pf = (PageFragment) getSupportFragmentManager().findFragmentByTag("android:switcher:" + R.id.theIdOfTheViewPager + ":" + viewPager.getCurrentItem());
pf.updateViews();

you could get the other two stored fragments(one in each side of the visible fragment) by modifying the value returned by viewPager.getCurrentItem() with -/+1;. Your fragments will need to be modified so in the onCreateView() you test if there is new data and use that.

If you use a FragmentStatePagerAdapter there are also ways of getting the current stored fragments.