Example of type-safe Fragment result contract extensions

TypedFragmentResults.kt

import android.os.Bundle
import androidx.core.os.bundleOf
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentManager
import androidx.fragment.app.FragmentResultListener
import androidx.lifecycle.LifecycleOwner


interface FragmentResultContract<T> {
    fun toBundle(result: T): Bundle
    fun fromBundle(bundle: Bundle): T
}

/**
 * Works with any value you can put in a Bundle: String?, Parcelable, Integer, Boolean, ...
 */
abstract class SingleValueFragmentResultContract<T> : FragmentResultContract<T> {
    override fun toBundle(result: T) = bundleOf(RESULT_KEY to result)

    @Suppress("UNCHECKED_CAST")
    override fun fromBundle(bundle: Bundle): T = bundle.get(RESULT_KEY) as T

    companion object {
        private const val RESULT_KEY = "result"
    }
}

fun <T> FragmentManager.setFragmentResult(contract: FragmentResultContract<T>, result: T) {
    setFragmentResult(contract::class.java.name, contract.toBundle(result))
}

inline fun <T> FragmentManager.setFragmentResultListener(contract: FragmentResultContract<T>,
                                                         lifecycleOwner: LifecycleOwner,
                                                         crossinline resultListener: (T) -> Unit) {
    setFragmentResultListener(contract::class.java.name, lifecycleOwner, FragmentResultListener { _, result ->
        resultListener(contract.fromBundle(result))
    })
}


class ConsumerFragment : Fragment() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        parentFragmentManager.setFragmentResultListener(ProducerFragment.ResultContract, this) { result ->
            println(result)
        }
    }
}

class ProducerFragment : Fragment() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        parentFragmentManager.setFragmentResult(ResultContract, "Hello World")
    }

    object ResultContract : SingleValueFragmentResultContract<String?>()
}