android - 如何在类中创建泛型类型的对象

Question

我有以下课程

open abstract class NexusAdapter<TData: NexusIdProvider, TViewHolder: NexusViewHolder<TData>>
                (protected val ctx: Context, private val _layoutId: Int, protected val items: List<TData>):
                BaseAdapter() {

    override fun getView(position: Int, view: View?, parent: ViewGroup?): View {
        val itemView = if (view == null)
            LayoutInflater.from(ctx).inflate(_layoutId, parent, false)
                else view!!

        // How do I create the object of type TViewHolder at runtime????
        var viewHolder: TViewHolder = TViewHolder::class.java.newInstance()

        viewHolder.bind(itemView , getItem(position))
        return itemView
    }

    //...
}

如何TViewHolder在我的类中创建类型的对象。

Answer 1

你不能做这个。您必须为其提供工厂方法。

要么在类中使用抽象函数

abstract fun createViewHolder(): TViewHolder

或将其作为参数提供给构造函数

abstract class NexusAdapter<TData: NexusIdProvider, TViewHolder: NexusViewHolder<TData>>(
        protected val ctx: Context,
        private val _layoutId: Int,
        protected val items: List<TData>,
        private val createViewHolder: () -> TViewHolder
) : BaseAdapter()