Kotlin One type argument expected for class for ab

问题:

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!

回答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:BaseSettingViewHolder<*>>:RecyclerView.Adapter<T>

5- Define out for abstract class type parameter.

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

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

回答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.