class FragmentB : Fragment() {
  // Fragment 간의 통신용 Listener 정의 
  interface OnResultListener {
    fun onResult(value: String)
  }
  
  private var listener: OnResultListener? = null
  ...
  // 외부에서 전달할 Setter Listener
  fun setListener(listener: OnResultListener) {
    this.listener = listener
  }

  private fun clickDone() {
    listener?.onResult(/** Write result */)
    parentFragmentManager.popBackStack()
  }  
}

class FragmentA : Fragment(), FragmentB.OnResultListener {
  ...
  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    ...
    // View가 Recreate시 처리
    val restoreValue = arguments?.getString(keyRestore)
    if (restoreValue != null) {
      /** action to do something */
    }
  }
  
  private fun showFragmentB() {
    parentFragmentManager.commit {
        replace(R.id.container, FragmentB().apply {
          // FragmentB 표시할때 Listener를 전달
          setListener(this@FragmentA)
        })
        addToBackStack(null)
      }
  }

  // Implement FragmentB.OnResultListener
  override fun onResult(value: String) {
    // Fragment가 Visible 중일때만 처리
    if (isVisible) {
      /** action to do something */
    } else {
      // Visible이 아닐 경우 Fragment#Arguemtn에 데이터 저장
      arguments = (arguments ?: Bundle()).also {
        it.putString(keyRestore, value)
      }
    }
  }
  companion object {
    private const val keyRestore = "resultRestore"
  }
}

// Result API
fun Fragment.setFragmentResult(
    requestKey: String,
    result: Bundle?
) = parentFragmentManager.setFragmentResult(requestKey, result)

// Result Listener API
fun Fragment.setFragmentResultListener(
    requestKey: String,
    listener: ((resultKey: String, bundle: Bundle) -> Unit)?
) {
    parentFragmentManager.setFragmentResultListener(requestKey, this, listener)
}

class FragmentA : Fragment() {
  ...  
  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    ...
    setFragmentResultListener("requestKey") { resultKey, result ->
      // Bundle[{key=value}]
      // action to do something
    }
    ...
  }
}

class FragmentB : Fragment() {
  ...
  private fun clickDone() {
    setFragmentResult("requestKey", bundleOf("key" to "value"))
    ...
  }  
  ...
}

import androidx.fragment.app.setFragmentResult

class FlexibleMasterFragment : ListFragment() {
  private val list = (0..20).map {
    "Item $it"
  }

  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    listAdapter = ArrayAdapter(requireContext(), android.R.layout.simple_list_item_1, list)
  }

  override fun onListItemClick(l: ListView, v: View, position: Int, id: Long) {
    super.onListItemClick(l, v, position, id)
    // Item Click시 setFragmentResult로 결과 전달
    setFragmentResult(requestKey, bundleOf(resultKey to list[position]))
  }

  companion object {
    // FragmentResult에 데이터 전달을 위한 RequestKey
    const val requestKey = "flexible"
    // Bundle에 저장할 데이터 Key
    const val resultKey = "item"
  }
}

class FlexibleDetailFragment : Fragment(R.layout.fragment_flexible_detail) {
  ...
  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    setFragmentResultListener(FlexibleMasterFragment.requestKey) { _, bundle ->
      binding.tvLabel.text = bundle.getString(FlexibleMasterFragment.resultKey)
    }
  }
}

// Fragment 에서 childFragmentManager를 사용한 FragmentResultListener Extension 
fun Fragment.setChildFragmentResultListener(
  requestKey: String,
  listener: ((resultKey: String, bundle: Bundle) -> Unit)?
) {
  childFragmentManager.setFragmentResultListener(requestKey, this, listener)
}

// FragmentActivity 에서 FragmentResultListener Extension 
fun FragmentActivity.setFragmentResultListener(
  requestKey: String,
  listener: ((resultKey: String, bundle: Bundle) -> Unit)?
) {
  supportFragmentManager.setFragmentResultListener(requestKey, this, listener)
}

import com.pluu.util.setFragmentResultListener

class BetweenStackActivity : AppCompatActivity() {
  override fun onCreate(savedInstanceState: Bundle?) {
    ...
    setFragmentResultListener(ResultConstract.keyRoot) { resultKey, result ->
      /** action to do something */ 
    }
  }
}

import androidx.fragment.app.setFragmentResult
import com.pluu.util.setChildFragmentResultListener

class BetweenStack1Fragment : Fragment(R.layout.fragment_between_stack1) {
  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    ...
    setChildFragmentResultListener(ResultConstract.keyStep1) { resultKey, result ->
      /** action to do something */ 
    }
    setChildFragmentResultListener(ResultConstract.keyRoot) { resultKey, result ->
      // ChildFragment인 BetweenStack2Fragment로부터 전달된 데이터를 ParentFragment로 전달
      setFragmentResult(resultKey, result)
    }
  }
}

import androidx.fragment.app.setFragmentResult
import com.pluu.util.setChildFragmentResultListener

class BetweenStack2Fragment : Fragment(R.layout.fragment_between_stack2) {
  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    ...
    setChildFragmentResultListener(ResultConstract.keyStep2) { resultKey, result ->
      /** action to do something */ 
    }
    setChildFragmentResultListener(ResultConstract.keyRoot) { resultKey, result ->
      // ChildFragment인 BetweenStack3Fragment로부터 전달된 데이터를 ParentFragment로 전달
      setFragmentResult(resultKey, result)
    }
    setChildFragmentResultListener(ResultConstract.keyStep1) { resultKey, result ->
      // ChildFragment인 BetweenStack3Fragment로부터 전달된 데이터를 ParentFragment로 전달
      setFragmentResult(resultKey, result)
    }
  }
}

import androidx.fragment.app.setFragmentResult
import androidx.fragment.app.setFragmentResultListener

class BetweenStackLastFragment : Fragment(R.layout.fragment_between_stack_last) {
  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    ...
    binding.btnConfirm.setOnClickListener {
      // End Point : BetweenStackActivity
      setFragmentResult(
        ResultConstract.keyRoot, bundleOf("key_string" to "==> root", "Int" to 0)
      )
      // End Point : BetweenStack1Fragment
      setFragmentResult(
        ResultConstract.keyStep1, bundleOf("key_string" to "==> stack1", "Int" to 1)
      )
      // End Point : BetweenStack2Fragment
      setFragmentResult(
        ResultConstract.keyStep2, bundleOf("key_string" to "==> stack2", "Int" to 2)
      )
      // End Point : BetweenStackLastFragment
      setFragmentResult(
        "current", bundleOf("key_string" to "==> current", "Int" to 3)
      )
    }

    setFragmentResultListener("current") { _, result ->
      /** action to do something */ 
    }
  }
}