Function in Kotlin data class as argument leads to

问题:

I have a data class in Kotlin hat is using the @Parcelize annotation for easy parcelization. Thing is I now want to pass a function to this class and I do not really know how to make the function not be considered during parceling.

This is my data class:

@Parcelize
data class GearCategoryViewModel(
        val title: String,
        val imageUrl: String,
        val categoryId: Int,
        val comingSoon: Boolean,
        @IgnoredOnParcel val onClick: (gearCategoryViewModel: GearCategoryViewModel) -> Unit
) : DataBindingAdapter.LayoutViewModel(R.layout.gear_category_item), Parcelable

I tried using @IgnoredOnParcel and @Transient without success.

This is the compile error I get:

Error:(20, 39) Type is not directly supported by 'Parcelize'. Annotate the parameter type with '@RawValue' if you want it to be serialized using 'writeValue()'

And this @RawValue annotation does not work either.

回答1:

Just cast lambda to serializable, and then create object from

@Parcelize
data class GearCategoryViewModel(
        val title: String,
        val imageUrl: String,
        val categoryId: Int,
        val comingSoon: Boolean,
        @IgnoredOnParcel val onClick: Serializable
) : DataBindingAdapter.LayoutViewModel(R.layout.gear_category_item), Parcelable {

    fun onClicked() = onClick as (gearCategoryViewModel: GearCategoryViewModel) -> Unit

    companion object {
        fun create(
                title: String,
                imageUrl: String,
                categoryId: Int,
                comingSoon: Boolean,
                onClick: (gearCategoryViewModel: GearCategoryViewModel) -> Unit
        ): GearCategoryViewModel = GearCategoryViewModel(
                title,
                imageUrl,
                categoryId,
                comingSoon,
                onClick as Serializable
        )
    }
}

回答2:

I know this isn't exactly a real answer but I would do it like this. Replace your function with class like this:

open class OnClick() : Parcelable {

    companion object {
        @JvmStatic
        fun fromLambda(func: (GearCategoryViewModel) -> Unit) = object : OnClick() {
            override fun invoke(param: GearCategoryViewModel) = func(param)
        }

        @JvmField
        val CREATOR = object : Parcelable.Creator<OnClick> {
            override fun createFromParcel(parcel: Parcel) = OnClick(parcel)

            override fun newArray(size: Int) = arrayOfNulls<OnClick>(size)
        }
    }

    constructor(parcel: Parcel) : this()

    open operator fun invoke(param: GearCategoryViewModel) {
        throw UnsupportedOperationException("This method needs to be implemented")
    }

    override fun writeToParcel(parcel: Parcel, flags: Int) = Unit

    override fun describeContents() = 0
}

And use it like this:

val onClick = OnClick.fromLambda { vm -> /* do something*/ }
onClick(viewModel);

回答3:

The premise of the question doesn't really make sense.

You can't deserialise this object if you don't serialise all of its properties.

You seem to want onClick to be null if this is deserialised, but even if that was possible, it'd throw a NPE because this property is not marked nullable.

Consider changing your architecture so you only serialise simple objects (POJOs or data classes) and not Functions.