Challenge 3: An Implicit Share Intent — Solution

// res/layout/activity_detail.xml — add a second Button
<Button
    android:id="@+id/shareButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Share" />

// DetailActivity.kt
class DetailActivity : AppCompatActivity() {
    private lateinit var binding: ActivityDetailBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityDetailBinding.inflate(layoutInflater)
        setContentView(binding.root)

        val message = intent.getStringExtra("MESSAGE") ?: "No message received"
        binding.detailText.text = message

        binding.shareButton.setOnClickListener {
            val shareIntent = Intent(Intent.ACTION_SEND).apply {
                type = "text/plain"
                putExtra(Intent.EXTRA_TEXT, binding.detailText.text.toString())
            }
            startActivity(Intent.createChooser(shareIntent, "Share via"))
        }
    }
}

Notes:
- This Intent is IMPLICIT — Intent(Intent.ACTION_SEND) doesn't name a
  destination class at all, only an action ("send this") plus data
  (type + EXTRA_TEXT). Android finds every installed app registered to
  handle ACTION_SEND with type "text/plain" and offers them as
  candidates.
- Intent.createChooser(shareIntent, "Share via") wraps the implicit
  Intent in a picker dialog that always appears, even if only one app
  could handle it — without createChooser, a single matching app might
  launch directly and silently become the user's permanent default for
  that action.
- binding.detailText.text.toString() reads whatever text is CURRENTLY
  displayed, so sharing works correctly regardless of what MESSAGE
  extra (or fallback) DetailActivity started with.