findFragmentById always returns null

Question

I\'m defining an ID for my fragment in the xml layout:

Answer 1

The reasons mentioned above are valid but another possible reason is that you are trying to search for the fragment while being in a fragment this also results in fragmentManager.findFragmentById to return null. We should use childFragmentManager.findFragmentById to find the fragment inside a fragment. According to the official documentation.

public final androidx.fragment.app.FragmentManager getChildFragmentManager()

Return a private FragmentManager for placing and managing Fragments inside of this Fragment.