NormalActivity.kt

class NormalActivity : AppCompatActivity(), NormalDialogFragment.NormalDialogListener {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_normal)

        val button = findViewById<Button>(R.id.normalButton)
        button.setOnClickListener { showNormalDialog() }
    }

    private fun showNormalDialog() =
        NormalDialogFragment.newInstance("Normal Dialog")
            .show(supportFragmentManager, "NormalDialog")

    override fun showNegativeToast() =
        Toast.makeText(this, "Negative button", Toast.LENGTH_SHORT).show()

    override fun showPositiveToast() =
        Toast.makeText(this, "Positive button", Toast.LENGTH_SHORT).show()
}

class NormalDialogFragment() : DialogFragment() {

    interface NormalDialogListener {
        fun showNegativeToast()
        fun showPositiveToast()
    }

    companion object {
        const val KEY_TITLE = "KEY_TITLE"

        fun newInstance(title: String) =
            NormalDialogFragment().apply {
                arguments = Bundle().apply {
                    putString(KEY_TITLE, title)
                }
            }
    }

    private val title by lazy { checkNotNull(arguments).getString(KEY_TITLE) }

    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        val listener = activity as NormalDialogFragment.NormalDialogListener
        return AlertDialog.Builder(activity)
            .setTitle(title)
            .setMessage("This is a normal dialog")
            .setPositiveButton("Continue") { dialog, which -> listener.showPositiveToast() }
            .setNegativeButton("Go back") { dialog, which -> listener.showNegativeToast() }
            .create()
    }
}