Fragmentで戻るボタンをoverride

appcompat:1.1.0-alpha04以降の場合はこう。

class MainFragment : Fragment() {
    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        activity?.onBackPressedDispatcher?.addCallback(this, object : OnBackPressedCallback {
            override fun handleOnBackPressed(): Boolean {
                // hogehoge
                return false
            }
        })
    }
}