Custom Parcelers

[gnawf]

I have an abstract class that I want to write a custom Parceler for per https://developer.android.com/kotlin/parcelize

e.g.

@Parcelize
data class User(val firstName: String, val lastName: String, val age: Int) : Parcelable {
    private companion object : Parceler<User> {
        override fun User.write(parcel: Parcel, flags: Int) {
            // Custom write implementation
        }

        override fun create(parcel: Parcel): User {
            // Custom read implementation
        }
    }
}

Cheers.

[arkivanov]

Hello! I never tried custom parcelers in multipaltform. But I think expect/actual should work fine.

// commonMain
expect data class User(...) : Parcelable

// androidMain
@Parcelize
actual data class User(...) : Parcelable {
    // Custom Parceler here
}

// Other source sets
actual data class User(...) : Parcelable

Please let me know if there are any issues.

[arkivanov]

Closing this for now. Feel free to reopen if there are any questions.

[gnawf]

Oh sorry, yes your suggestion worked 😄. From memory though, it involved a little bit of boilerplate, so a multiplatform option built into Essenty would be nice.

[xxfast]

would be nice if we can support TypeParceler<ExternalClass, ExternalClassParceler> in common code, but totally understand if we cant

[arkivanov]

@xxfast This would require expect/actual the whole Parcel class. Meantime, it's possible to expect/actual custom parcelers in the following way.

// commonMain

expect interface Parceler<T>

@OptIn(ExperimentalMultiplatform::class)
@OptionalExpectation
@Target(AnnotationTarget.TYPE)
expect annotation class WriteWith<P : Parceler<*>>()

// androidMain

actual typealias Parceler<T> = kotlinx.parcelize.Parceler<T>

actual typealias WriteWith<P> = kotlinx.parcelize.WriteWith<P>

// nonAndroidMain - a shared source source for al targets except Android

actual interface Parceler<T>

After that you can expect/actual your custom parcelers as follows.

// commonMain

class ExternalClass(val value: Int)

expect object ExternalClassParceler : Parceler<ExternalClass>

@Parcelize
class MyClass(val external: @WriteWith<ExternalClassParceler> ExternalClass) : Parcelable

// androidMain

actual object ExternalClassParceler : Parceler<ExternalClass> {
    override fun create(parcel: Parcel): ExternalClass = ExternalClass(parcel.readInt())

    override fun ExternalClass.write(parcel: Parcel, flags: Int) {
        parcel.writeInt(value)
    }
}

// nonAndroidMain

actual object ExternalClassParceler : Parceler<ExternalClass>

Yes, there is some boilerplate, but at least it works. It should be also possible to expect/actual Parcel, with only required methods. In this case Parcelerwould be placed fully incommonMainwithout expect/actual. And so custom parcelers could be placed incommonMain` as well.

[arkivanov]

Converted this issue to a discussion for transparency.

[xxfast]

I know this is a couple of months late - but just wanted to say that the above approach works 👍 thanks @arkivanov

Just curious - why was Parceler and WriteWith not included in com.arkivanov.essenty.parcelable?

[arkivanov]

Just curious - why was Parceler and WriteWith not included in com.arkivanov.essenty.parcelable?

There are no specific reasons, we can easily add it! I have filed #51. I would gratefully accept a contribution here, in case someone would like to contribute.

[xxfast]

@arkivanov Done #52

[arkivanov]

Version 0.4.0 is released with Parceler and WriteWith APIs. Thanks everyone for raising this and use cases, and thanks @xxfast for your contribution!