ViewPager retaing old Fragments on screen rotation

问题

I am using ViewPager and FragmentStatePagerAdapter to show fragment. Initially there are 2 fragments added Fragment1 and Fragment2 and 3rd fragment Fragment3 is added at 2nd position after recieiving response from server. So after all pages are added this should be sequence of Fragments in ViewPager --> Fragment1, Fragment3, Fragment2.

The Problem is after Fragment1 and Fragment3 are added and app is making server call before adding 3rd Fragment at 2nd position if I do screen rotation multiple time then after 3rd fragment is added it still shows old copy of Fragment2 which was at 2nd position initially at 2nd position and 3rd position have new copy of Fragment2. So Fragment3 doest shows up in ViewPager. Sequence after adding 3rd Fragment -- > Fragment1, old copy of Fragment2, New Fragment2.

I am overriding onSaveInstanceState and calling super.onSaveInstanceState in my Activity.

Also I have tried returning POSITION_NONE from getItemPosition. I read somewhere that ViewPager save copies of fragment. Also through debugging I checked that ViewPager contained 2 copies of Fragment2 when issue was reproduced even though getItem of FragmentStatePagerAdapter returned different Fragments for each position but still at 2nd position it was showing old fragment. For testing purpose in getItem I returned Fragment1 for all positions so that all 3 pages should be same but even after that in 2nd position it was showing old copy of Fragment2 when I reproduced issue with steps mentioned above.

So how to clear ViewPager so that it does not save old fragments. How to refresh ViewPager so that it does not retain old copy with fragments. I think problem is with onSaveInstanceState but I need it. How can I exclude ViewPager when views are saved in onSaveInstanceState. I have tried mViewPager.setSaveEnabled(false) but it takes too much memory.

I found that the problem is instantiateItem method of adapter does not call getItem due to which old fragment is returned.

Below is solution code

Code:

 @Override
        public Object instantiateItem(ViewGroup container, int position) {
            Object obj = super.instantiateItem(container, position);
            Fragment fragment = mFragments.get(position);

            if((obj!=null && fragment!=null) && !(obj.getClass().getSimpleName().equals(fragment.clss.getSimpleName()))){
                destroyItem(container, position, obj);
                return super.instantiateItem(container, position);
            }else{
                return obj;
            }
        }

回答1:

Only override this method in FragmentpagerAdapter

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
       // TODO Auto-generated method stub
       super.destroyItem(ViewGroup container, int position, Object object);
}

then remove super.destroyItem(ViewGroup container, int position, Object object); from your code

回答2:

I solved the problem, I am posting my solution here. I override instantiateItem of FragmentStatePagerAdapter and inside it I am getting object from super.instantiateItem and comparing its classname with classname of object at that position from list of fragments that I am maintaining.

If classname is not same its mean super.instantiateItem returns duplicate fragment. So I am calling destroyItem at that position and again calling super.instantiateItem and returning it from instantiateItem.

FragmentStatePagerAdapter return old fragment because in framework code arraylist mFragments has duplicate fragment and it just return fragment at current position. I think it should compare fragment at the position in list with currently displaying fragment before returning it.

来源：https://stackoverflow.com/questions/18544698/viewpager-retaing-old-fragments-on-screen-rotation

标签

android

android-fragments

android-viewpager