Remove Fragment Page from ViewPager in Android

The ViewPager doesn't remove your fragments with the code above because it loads several views (or fragments in your case) into memory. In addition to the visible view, it also loads the view to either side of the visible one. This provides the smooth scrolling from view to view that makes the ViewPager so cool.

To achieve the effect you want, you need to do a couple of things.

1. Change the FragmentPagerAdapter to a FragmentStatePagerAdapter. The reason for this is that the FragmentPagerAdapter will keep all the views that it loads into memory forever. Where the FragmentStatePagerAdapter disposes of views that fall outside the current and traversable views.

2. Override the adapter method getItemPosition (shown below). When we call mAdapter.notifyDataSetChanged(); the ViewPager interrogates the adapter to determine what has changed in terms of positioning. We use this method to say that everything has changed so reprocess all your view positioning.

And here's the code...

private class MyPagerAdapter extends FragmentStatePagerAdapter {

    //... your existing code

    @Override
    public int getItemPosition(Object object){
        return PagerAdapter.POSITION_NONE;
    }

}

The solution by Louth was not enough to get things working for me, as the existing fragments were not getting destroyed. Motivated by this answer, I found that the solution is to override the getItemId(int position) method of FragmentPagerAdapter to give a new unique ID whenever there has been a change in the expected position of a Fragment.

Source Code:

private class MyPagerAdapter extends FragmentPagerAdapter {

    private TextProvider mProvider;
    private long baseId = 0;

    public MyPagerAdapter(FragmentManager fm, TextProvider provider) {
        super(fm);
        this.mProvider = provider;
    }

    @Override
    public Fragment getItem(int position) {
        return MyFragment.newInstance(mProvider.getTextForPosition(position));
    }

    @Override
    public int getCount() {
        return mProvider.getCount();
    }


    //this is called when notifyDataSetChanged() is called
    @Override
    public int getItemPosition(Object object) {
        // refresh all fragments when data set changed
        return PagerAdapter.POSITION_NONE;
    }


    @Override
    public long getItemId(int position) {
        // give an ID different from position when position has been changed
        return baseId + position;
    }

    /**
     * Notify that the position of a fragment has been changed.
     * Create a new ID for each position to force recreation of the fragment
     * @param n number of items which have been changed
     */
    public void notifyChangeInPosition(int n) {
        // shift the ID returned by getItemId outside the range of all previous fragments
        baseId += getCount() + n;
    }
}

Now, for example if you delete a single tab or make some change to the order, you should call notifyChangeInPosition(1) before calling notifyDataSetChanged(), which will ensure that all the Fragments will be recreated.

Why this solution works

Overriding getItemPosition():

When notifyDataSetChanged() is called, the adapter calls the notifyChanged() method of the ViewPager which it is attached to. The ViewPager then checks the value returned by the adapter's getItemPosition() for each item, removing those items which return POSITION_NONE (see the source code) and then repopulating.

Overriding getItemId():

This is necessary to prevent the adapter from reloading the old fragment when the ViewPager is repopulating. You can easily understand why this works by looking at the source code for instantiateItem() in FragmentPagerAdapter.

    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));
    }

As you can see, the getItem() method is only called if the fragment manager finds no existing fragments with the same Id. To me it seems like a bug that the old fragments are still attached even after notifyDataSetChanged() is called, but the documentation for ViewPager does clearly state that:

Note this class is currently under early design and development. The API will likely change in later updates of the compatibility library, requiring changes to the source code of apps when they are compiled against the newer version.

So hopefully the workaround given here will not be necessary in a future version of the support library.