How to implement ViewHolder using sealed class in Kotlin

问题

I saw an interesting viewholder implementation in this tweet https://twitter.com/AndroidDev/status/972502799496790018

override fun onBindViewHolder(holder: SealedAdapterViewHolder, position: Int) {
  return when (holder) {
    is HeaderHolder -> holder.displayHeader(items[position])
    is DetailsHolder -> holder.displayDetails(items[position])
  }
}

Unfortunately i can't figure out how to implement thouse holders. And I didn't find any examples of this trick.

In my viewholders I have to extend RecyclerView.ViewHolder and I have to extend sealed class so i can use it in "when clauses". Multiple inharitance is not allowed.

So is it possible and if it is then how?

P.S.

original authors write this:

You can also use sealed classes in a RecyclerView adapter. They’re a perfect fit for ViewHolders - with a clean set of types to dispatch explicitly to each holder. Used as an expression, the compiler will error if all types aren’t matched.

回答1:

Something like this:

sealed class SealedAdapterViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

    class HeaderHolder(view: View) : SealedAdapterViewHolder(view)

    class DetailsHolder(view: View) : SealedAdapterViewHolder(view)
}

回答2:

it's in the first post of the thread.

fun foo(holder : SealedAdapterViewHolder){
    when (holder) {
       is HeaderHolder -> holder.displayHeader(items[position])
       is DetailsHolder -> holder.displayDetails(items[position])
    }
}

sealed class SealedAdapterViewHolder(view: View) : RecyclerView.ViewHolder(view)
data class HeaderHolder(val view: View): SealedAdapterViewHolder(view){
    fun displayHeader(...){}
}
data class DetailsHolder(val view: View): SealedAdapterViewHolder(view){
    fun displayDetails(...){}
}

来源：https://stackoverflow.com/questions/49234841/how-to-implement-viewholder-using-sealed-class-in-kotlin

标签

android

android-recyclerview

kotlin

sealed