Challenge 1: A Basic Fragment — Solution

// fragment_welcome.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:id="@+id/welcomeText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Welcome!" />

</LinearLayout>

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

// activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragmentContainer"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

// MainActivity.kt
class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        if (savedInstanceState == null) {
            supportFragmentManager.beginTransaction()
                .replace(R.id.fragmentContainer, WelcomeFragment())
                .commit()
        }
    }
}

Notes:
- WelcomeFragment.onCreateView inflates fragment_welcome.xml and returns
  it — the returned View is what the FragmentManager places into
  fragmentContainer.
- The "if (savedInstanceState == null)" check prevents a duplicate
  WelcomeFragment from being added every time the Activity recreates
  (e.g. on rotation) — the FragmentManager already automatically
  restores whatever Fragment was showing before recreation.
- replace(R.id.fragmentContainer, WelcomeFragment()) is used even for
  this very first load, since it's the standard call whether adding a
  Fragment for the first time or swapping one out later (Challenge 2).