ParcelableArgs and ParcelableState

ParcelableArgs.kt

/*
 * Copyright (c) 2020 Hai Zhang <dreaming.in.code.zh@gmail.com>
 * All Rights Reserved.
 */

package com.example.yourapplication

import android.app.Activity
import android.content.Intent
import android.os.Bundle
import android.os.Parcelable
import androidx.annotation.MainThread
import androidx.fragment.app.Fragment
import kotlin.reflect.KClass

interface ParcelableArgs : Parcelable

fun <Args : ParcelableArgs> Bundle.putArgs(args: Args, argsClass: KClass<Args>): Bundle {
    putParcelable(argsClass.java.name, args)
    return this
}

inline fun <reified Args : ParcelableArgs> Bundle.putArgs(args: Args) = putArgs(args, Args::class)

fun <Args : ParcelableArgs> Args.toBundle(argsClass: KClass<Args>): Bundle =
    Bundle().apply { putArgs(this@toBundle, argsClass) }

inline fun <reified Args : ParcelableArgs> Args.toBundle(): Bundle = toBundle(Args::class)

fun <F: Fragment, Args: ParcelableArgs> F.putArgs(args: Args, argsClass: KClass<Args>): F {
    val arguments = arguments
    if (arguments != null) {
        arguments.putArgs(args, argsClass)
    } else {
        this.arguments = args.toBundle(argsClass)
    }
    return this
}

inline fun <F: Fragment, reified Args: ParcelableArgs> F.putArgs(args: Args): F =
    putArgs(args, Args::class)

fun <Args: ParcelableArgs> Intent.putArgs(args: Args, argsClass: KClass<Args>): Intent =
    putExtra(argsClass.java.name, args)

inline fun <reified Args: ParcelableArgs> Intent.putArgs(args: Args) = putArgs(args, Args::class)

fun <Args : ParcelableArgs> Bundle.getArgs(argsClass: KClass<Args>): Args {
    classLoader = argsClass.java.classLoader
    return getParcelable(argsClass.java.name, argsClass)!!
}

inline fun <reified Args : ParcelableArgs> Bundle.getArgs() = getArgs(Args::class)

@MainThread
inline fun <reified Args : ParcelableArgs> Activity.args() = BundleArgsLazy(Args::class) {
    intent.extras ?: throw IllegalStateException("Activity $this has null intent extras")
}

@MainThread
inline fun <reified Args : ParcelableArgs> Fragment.args() = BundleArgsLazy(Args::class) {
    arguments ?: throw IllegalStateException("Fragment $this has null arguments")
}

class BundleArgsLazy<Args : ParcelableArgs>(
    private val argsClass: KClass<Args>,
    private val argumentsProducer: () -> Bundle
) : Lazy<Args> {
    private var cached: Args? = null

    override val value: Args
        get() {
            var args = cached
            if (args == null) {
                args = argumentsProducer().getArgs(argsClass)
                cached = args
            }
            return args
        }

    override fun isInitialized() = cached != null
}

ParcelableState.kt

/*
 * Copyright (c) 2020 Hai Zhang <dreaming.in.code.zh@gmail.com>
 * All Rights Reserved.
 */

package com.example.yourapplication

import android.os.Bundle
import android.os.Parcelable
import kotlin.reflect.KClass

interface ParcelableState : Parcelable

fun <State : ParcelableState> Bundle.putState(state: State) =
    putParcelable(state.javaClass.name, state)

fun <State : ParcelableState> Bundle.getState(stateClass: KClass<State>): State {
    classLoader = stateClass.java.classLoader
    return getParcelable(stateClass.java.name, stateClass)!!
}

inline fun <reified State : ParcelableState> Bundle.getState() = getState(State::class)

SampleUsages.kt

/*
 * Copyright (c) 2020 Hai Zhang <dreaming.in.code.zh@gmail.com>
 * All Rights Reserved.
 */

package com.example.yourapplication

import android.content.Intent
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.fragment.app.Fragment
import androidx.fragment.app.add
import androidx.fragment.app.commit
import kotlinx.android.parcel.Parcelize

class SampleActivity : AppCompatActivity() {
    private val args by args<Args>()

    fun addSampleFragment() {
        supportFragmentManager.commit {
            add<SampleFragment>(android.R.id.content, null, SampleFragment.Args(0, null, Bundle()).toBundle())
        }
    }

    @Parcelize
    data class Args(
        val intArgument: Int,
        val nullableStringArgument: String?,
        val parcelableArgument: Bundle
    ) : ParcelableArgs
}

class SampleFragment : Fragment() {
    private val args by args<Args>()

    fun startSampleActivity() {
        startActivity(
            Intent(requireContext(), SampleActivity::class.java).putArgs(SampleActivity.Args(0, null, Bundle()))
        )
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        val state = savedInstanceState?.getState<State>()
        val intValue = state?.intState ?: args.intArgument
    }

    override fun onSaveInstanceState(outState: Bundle) {
        super.onSaveInstanceState(outState)

        outState.putState(State(false))
    }

    @Parcelize
    data class Args(
        val intArgument: Int,
        val nullableStringArgument: String?,
        val parcelableArgument: Bundle
    ) : ParcelableArgs

    @Parcelize
    private data class State(
        val intState: Int
    ) : ParcelableState
}