Kotlin One type argument expected for class for abstract generic view holder

Question

I'm trying to create a RecyclerView.Adapter with the following:

---

View holders - Provided the abstract parent and one son

abstract class BaseSettingsViewHolder<T>(var viewDataBinding :  ViewDataBinding) : RecyclerView.ViewHolder(viewDataBinding.root) {     abstract fun onBind(data: T, presenter: ISettingsPresenter, position: Int) } 

---

class SettingsTitleViewHolder(viewDataBinding: ViewDataBinding) : BaseSettingsViewHolder<TitleData>(viewDataBinding) {      override fun onBind(data: TitleData, presenter: ISettingsPresenter, position: Int) {         viewDataBinding.setVariable(BR.titleData, data)         viewDataBinding.setVariable(BR.itemPosition, position)         viewDataBinding.setVariable(BR.settingsPresenter, presenter)         viewDataBinding.executePendingBindings()     }  } 

And when trying to declare the adapter:

class SettingsAdapter(var context: Context, var presenter: ISettingsPresenter) : RecyclerView.Adapter<BaseSettingsViewHolder>() { 

I'm getting "One type argument expected for class" compile error on the:

RecyclerView.Adapter<BaseSettingsViewHolder> 

Appreciate the help!

Answer 1

1- If you use always SettingTitleViewHolder;

RecyclerView.Adapter<SettingTitleViewHolder> 

2- If you want to use any class which extended BaseSettingViewHolder;

RecyclerView.Adapter<BaseSettingsViewHolder<*>> 

3- Use Any Object Type

RecyclerView.Adapter<BaseSettingsViewHolder<Any>> 

4- Use extended type parameter for adapter class

class SettingsMenuAdapter<T>:RecyclerView.Adapter<T> where : BaseSettingViewHolder<*> 

5- Define out for abstract class type parameter.

abstract class BaseSettingsViewHolder<out T> RecyclerView.Adapter<BaseSettingsViewHolder<Any>> 

7- Read that article => "Generics in Kotlin" ;)

Answer 2

You should specify the type argument for the BaseSettingsViewHolder in the RecyclerView.Adapter<BaseSettingsViewHolder> type.

Kotlin, unlike Java, does not have the raw types, so you cannot simply omit the type arguments.

The closest concept to raw types is star-projected types: use BaseSettingsViewHolder<*> in RecyclerView.Adapter<BaseSettingsViewHolder<*>>, this will mean that the type argument for BaseSettingsViewHolder is unknown.