FragmentPagerAdapter is not removing items (Fragments) correctly

Question

I have implemented the FragmentPagerAdapter and and using a List to hold all fragments for my ViewPager to display. On

Answer 1

I got same problem,and my solution was overring the method "destroyItem" as following.

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    FragmentManager manager = ((Fragment)object).getFragmentManager();
    FragmentTransaction trans = manager.beginTransaction();
    trans.remove((Fragment)object);
    trans.commit();
}

It's work for me,does anybody have another solutions?

Updated:

I found those code made Fragment removed unnecessary,so I added a condition to avoid it.

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    if (position >= getCount()) {
        FragmentManager manager = ((Fragment) object).getFragmentManager();
        FragmentTransaction trans = manager.beginTransaction();
        trans.remove((Fragment) object);
        trans.commit();
    }
}

Answer 2

Didn't work out for me. My solution was put FragmentStatePagerAdapter.java in my project, renamed to FragmentStatePagerAdapter2.java. In destroyItem(), I changed a little based on error logs. From

// mFragments.set(position, null);

to

if (position < mFragments.size())mFragments.remove(position);

Maybe you don't have the same problem, just check the log.Hope this helps someone!

Answer 3

After a lot of trying, i got it to work so that it removes or attaches a third fragment at the end position correctly.

Object fragments[] = new Object[3];
int mItems = 2;
MyAdapter mAdapter;
ViewPager mPager;


public void addFragment(boolean bool) {

    mAdapter.startUpdate(mPager);

    if (!bool) {
        mAdapter.destroyItem(mPager, 2, fragments[2]);
        mItems = 2;
        fNach = false;
    }
    else if (bool && !fNach){
        mItems = 3;
        mAdapter.instantiateItem(mPager,2);
        fNach = true;
    }
    mAdapter.finishUpdate(mPager);
    mAdapter.notifyDataSetChanged();

}

public class MyAdapter extends FragmentPagerAdapter {
    MyAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public int getCount() {
        return mItems;
    }

    @Override
    public CharSequence getPageTitle(int position) {
    ... (code for the PagerTitleStrip)
    }

    @Override
    public Fragment getItem(int position) {
        Fragment f = null;
        switch (position) {
            case 0:
                f = new Fragment1();
                break;
            case 1:
                f = new Fragment2();
                break;
            case 2:
                f = new Fragment3();
                break;
        }
        return f;
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        Object o = super.instantiateItem(container,position);
        fragments[position] = o;
        return o;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        super.destroyItem(container, position, object);
        System.out.println("Destroy item " + position);
        if (position >= getCount()) {
                FragmentManager manager = ((Fragment) object).getFragmentManager();
                FragmentTransaction ft = manager.beginTransaction();
                ft.remove((Fragment) object);
                ft.commit();
        }

    }
}

Some clarification: to get the object reference to call destroyItem, i stored the objects returned from instantiateItem in an Array. When you are adding or removing fragments, you have to announce it with startUpdate, finishUpdate and notifyDataSetChanged. The number of items have to be changed manually, for adding you increase it and instantiate it, getItem creates it then. For deletion, you call destroyItem, and in this code, it is essential the position >= mItems, because destroyItem is also called if a fragment goes out of the cache. You don't want to delete it then. The only thing which doesn't work is the swiping animation. After removing the last page, the "cannot swipe left" animation is not restored correctly on the new last page. If you swipe it, a blank page is shown and it bounces back.

Answer 4

Taking "the best of both worlds" (I mean the answers by @Tericky Shih and @mikepenz) we have it short and simple:

public class MyPagerAdapter extends FragmentPagerAdapter {

    public ArrayList<Fragment> fragments = new ArrayList<Fragment>();    

    ...

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        super.destroyItem(container, position, object);
        if (position >= getCount()) fm.beginTransaction().remove((Fragment) object).commit();
    }

    @Override
    public int getItemPosition(Object object) {
        if (fragments.contains(object)) return fragments.indexOf(object);
        else return POSITION_NONE;
    }
}

The main difference is that if some fragment is not changed you don't have to destroy its view and don't have to return POSITION_NONE for it. At the same time, I've encountered a situation when ViewPager was holding a reference to an item which was already destroyed, therefore the check if (fragments.contains(object)) helps to determine if that item is not needed anymore.

Answer 5

I had a situation similar to yours. I recently needed to add and remove Fragments from the ViewPager. In the first mode, I have Fragments 0, 1, and 2 and in the second mode I have Fragments 0 and 3. I want Fragment 0 to be same for both modes and hold over information.

All I needed to do was override FragmentPagerAdapter.getItemId to make sure that I returned a unique number for each different Fragment - the default is to return "position". I also had to set the adapter in the ViewPager again - a new instance will work but I set it back to the same instance. Setting the adapter results in the ViewPager removing all the views and trying to add them again.

However, the trick is that the adapter only calls getItem when it wants to instantiate the Fragment - not every time it shows it. This is because they are cached and looks them up by the "position" returned by getItemId.

Imagine you have three Fragments (0, 1 and 2) and you want to remove "1". If you return "position" for getItemId then removing Fragment 1 will not work because when you try to show Fragment 2 after deleting Fragment 1 the pager/adapter will think it's already got the Fragment for that "position" and will continue to display Fragment 1.

FYI: I tried notifyDataSetChanged instead of setting the adapter but it didn't work for me.

First, the getItemId override example and what I did for my getItem:

public class SectionsPagerAdapter extends FragmentPagerAdapter
{
    ...

    @Override
    public long getItemId(int position)
    {
        // Mode 1 uses Fragments 0, 1 and 2. Mode 2 uses Fragments 0 and 3
        if ( mode == 2 && position == 1 )
            return 3;
        return position;
    }

    @Override
    public Fragment getItem(int position)
    {
        if ( mode == 1 )
        {
            switch (position)
            {
                case 0:
                    return <<fragment 0>>;
                case 1:
                    return <<fragment 1>>;
                case 2:
                    return <<fragment 2>>;
            }
        }
        else    // Mode 2
        {
            switch (position)
            {
                case 0:
                    return <<fragment 0>>;
                case 1:
                    return <<fragment 3>>;
            }
        }
        return null;
    }
}

Now the change of mode:

private void modeChanged(int newMode)
{
    if ( newMode == mode )
        return;

    mode = newMode;

    // Calling mSectionsPagerAdapter.notifyDataSetChanged() is not enough here
    mViewPager.setAdapter(mSectionsPagerAdapter);
}

Answer 6

The real problem is that FragmentPagerAdapter uses the position of the fragment in your list as ID. So if you add a new List or simply remove items "instantiateItem" item will find different fragments for new items in list...

@Override
public Object instantiateItem(ViewGroup container, int position) {
    if (mCurTransaction == null) {
        mCurTransaction = mFragmentManager.beginTransaction();
    }

    final long itemId = getItemId(position);

    // Do we already have this fragment?
    String name = makeFragmentName(container.getId(), itemId);
    Fragment fragment = mFragmentManager.findFragmentByTag(name);
    if (fragment != null) {
        if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
        mCurTransaction.attach(fragment);
    } else {
        fragment = getItem(position);
        if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
        mCurTransaction.add(container.getId(), fragment,
                makeFragmentName(container.getId(), itemId));
    }
    if (fragment != mCurrentPrimaryItem) {
        fragment.setMenuVisibility(false);
        fragment.setUserVisibleHint(false);
    }

    return fragment;
}

and

  private static String makeFragmentName(int viewId, long id) {
    return "android:switcher:" + viewId + ":" + id;
}

and

     * Return a unique identifier for the item at the given position.
 * <p>
 * <p>The default implementation returns the given position.
 * Subclasses should override this method if the positions of items can change.</p>
 *
 * @param position Position within this adapter
 * @return Unique identifier for the item at position
 */
public long getItemId(int position) {
    return position;
}