Challenge 2: Pass an Argument with SafeArgs — Solution

// app/build.gradle.kts (or the project-level build.gradle.kts, depending
// on Gradle version) — add the SafeArgs plugin
plugins {
    id("androidx.navigation.safeargs.kotlin")
}

// res/navigation/nav_graph.xml — declare the argument on detailsFragment
<fragment
    android:id="@+id/detailsFragment"
    android:name=".DetailsFragment"
    android:label="Details">
    <argument
        android:name="message"
        app:argType="string" />
</fragment>

// WelcomeFragment.kt — sending, via the generated Directions class
binding.viewDetailsButton.setOnClickListener {
    val action = WelcomeFragmentDirections.actionWelcomeToDetails(message = "Hello from Welcome!")
    findNavController().navigate(action)
}

// DetailsFragment.kt — receiving, via the generated Args class
class DetailsFragment : Fragment() {
    private lateinit var binding: FragmentDetailsBinding
    private val args: DetailsFragmentArgs by navArgs()

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

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding.detailText.text = args.message
    }
}

Notes:
- WelcomeFragmentDirections.actionWelcomeToDetails(...) and
  DetailsFragmentArgs are BOTH generated automatically by the SafeArgs
  plugin from the nav graph's <argument> declaration — neither class is
  hand-written.
- The parameter name (message) is checked by the compiler at the call
  site — passing the wrong type, or forgetting a required argument
  entirely, is a compile error, not a runtime crash the way a mistyped
  Intent extra key would be (Chapter 4).
- val args: DetailsFragmentArgs by navArgs() uses Kotlin's property
  delegation (Kotlin Intermediate Chapter 4) — navArgs() is itself a
  delegate that reads the Fragment's arguments Bundle and exposes it as
  a typed args object.