How to get elements of fragments created by ViewPager in MainActivity?

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Unfortunately the only “safe” way to do it is to check the source code of FragmentPagerAdapter, and see what tag is the fragment is added with – because findFragmentByTag is the only safe way to get a Fragment from a FragmentManager.

Of course, we need to hope that this implementation detail doesn’t change between support library versions, but it actually hasn’t changed in years 🙂

Anyways, so FragmentPagerAdapter says:

    // Do we already have this fragment?
    String name = makeFragmentName(container.getId(), itemId);
    Fragment fragment = mFragmentManager.findFragmentByTag(name);

So what is name?

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

What is viewId and what is id?

ViewId is container.getId(), where container is the ViewPager itself.

id is: final long itemId = getItemId(position); which by default is return position;.

So you can find the Fragment as follows:

Fragment fragment = fragmentManager.findFragmentByTag("android:switcher:" + viewPager.getId() + ":" + fragmentPosition);
// if fragment is null, it was not created yet by ViewPager

NOTE:

It is worth noting that you should NOT rely on getItem(int position) { to return the same fragment instance as you passed in, because that will lead you to this problem. (This question does it correctly, the getItem() method must always return a new Fragment instance.)

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