Challenge 2: Swapping Fragments — Solution

// fragment_welcome.xml — add a Button
<Button
    android:id="@+id/viewDetailsButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="View Details" />

// WelcomeFragment.kt
class WelcomeFragment : Fragment() {
    private lateinit var binding: FragmentWelcomeBinding

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
    ): View {
        binding = FragmentWelcomeBinding.inflate(inflater, container, false)
        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding.viewDetailsButton.setOnClickListener {
            parentFragmentManager.beginTransaction()
                .replace(R.id.fragmentContainer, DetailsFragment())
                .commit()
        }
    }
}

// fragment_details.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Details screen" />

</LinearLayout>

// DetailsFragment.kt
class DetailsFragment : Fragment() {
    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
    ): View {
        return inflater.inflate(R.layout.fragment_details, container, false)
    }
}

Notes:
- parentFragmentManager (accessed from inside a Fragment) is the
  Fragment-side equivalent of the Activity's supportFragmentManager used
  in Challenge 1 — both refer to the same underlying FragmentManager.
- replace(R.id.fragmentContainer, DetailsFragment()) removes
  WelcomeFragment from the container and puts DetailsFragment in its
  place — the same container ID from activity_main.xml is reused, since
  it's the Activity's layout that hosts whichever Fragment is currently
  active.
- The click listener is set up in onViewCreated (not onCreateView),
  following this chapter's guidance that Views should be configured
  after they're confirmed to exist, not while they're still being
  inflated.