[android] Remove Fragment Page from ViewPager in Android

Louth's answer works fine. But I don't think always return POSITION_NONE is a good idea. Because POSITION_NONE means that fragment should be destroyed and a new fragment will be created. You can check that in dataSetChanged function in the source code of ViewPager.

        if (newPos == PagerAdapter.POSITION_NONE) {
            mItems.remove(i);
            i--;
            ... not related code
            mAdapter.destroyItem(this, ii.position, ii.object);

So I think you'd better use an arraylist of weakReference to save all the fragments you have created. And when you add or remove some page, you can get the right position from your own arraylist.

 public int getItemPosition(Object object) {
    for (int i = 0; i < mFragmentsReferences.size(); i ++) {
        WeakReference<Fragment> reference = mFragmentsReferences.get(i);
        if (reference != null && reference.get() != null) {
            Fragment fragment = reference.get();
            if (fragment == object) {
                return i;
            }
        }
    }
    return POSITION_NONE;
}

According to the comments, getItemPosition is Called when the host view is attempting to determine if an item's position has changed. And the return value means its new position.

But this is not enought. We still have an important step to take. In the source code of FragmentStatePagerAdapter, there is an array named "mFragments" caches the fragments which are not destroyed. And in instantiateItem function.

if (mFragments.size() > position) {
        Fragment f = mFragments.get(position);
        if (f != null) {
            return f;
        }
    }

It returned the cached fragment directly when it find that cached fragment is not null. So there is a problem. From example, let's delete one page at position 2, Firstly, We remove that fragment from our own reference arraylist. so in getItemPosition it will return POSITION_NONE for that fragment, and then that fragment will be destroyed and removed from "mFragments".

 mFragments.set(position, null);

Now the fragment at position 3 will be at position 2. And instantiatedItem with param position 3 will be called. At this time, the third item in "mFramgents" is not null, so it will return directly. But actually what it returned is the fragment at position 2. So when we turn into page 3, we will find an empty page there.

To work around this problem. My advise is that you can copy the source code of FragmentStatePagerAdapter into your own project, and when you do add or remove operations, you should add and remove elements in the "mFragments" arraylist.

Things will be simpler if you just use PagerAdapter instead of FragmentStatePagerAdapter. Good Luck.