如何使用kotlin创建在构造函数中传递方法引用的泛型类的实例

Question

Now that I'm using kotlin as my main programing language I'm trying to simplify Android's Recyclerview implementation logic and I'm stuck at following point:

Let's say I have defined the following ViewHolder class, where a click position event is propagated via a method reference in the constructor.

class CustomViewHolder(itemView: View, val onClick: (Int) -> Unit)) : RecyclerView.ViewHolder(itemView){
    itemView.setOnClickListener {
        onClick.invoke(adapterPosition)
    } 
}

How could I build an instance of a generic class that has a method reference in the constructor?

My recyclerview implementation has a generic class in the constructor and also an entity reference to be able to create an instance of my CustomViewHolder class by reflection at onCreateViewHolder:

class CustomAdapter<HolderClassGeneric>(val entityClass: Class<HolderClassGeneric>) : RecyclerView.Adapter<HolderClassGeneric>() {

    /*
    Usual recyclerview stuff
    */ 

    //Method that I want to be called when a list item is clicked
    fun onListItemClicked(position: Int) {
       //do stuff
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): HolderClassGeneric {
        val view = LayoutInflater.from(parent.context).inflate(listItemLayoutResourceId, parent, false)

        val constructor: Constructor<HolderClassGeneric>
        val instance: HolderClassGeneric
                                                            //I'M STUCK HERE
        constructor = entityClass.getConstructor(View::class.java, ?¿?¿?¿?¿)
        instance = constructor.newInstance(view, this::onListItemClicked)

        return instance

}

If what I want to achieve is not possible, would it be possible to pass the method reference using a setter by reflection?

Answer 1

Kotlin lambda通常被翻译为FunctionX对象，X是它所拥有的参数的数量，所以如果你正在寻找像(Int) -> Unit这样的lambda函数的表示，那么它将是Function1<Int, Unit> so你可以这样做：

entityClass.getConstructor(View::class.java, Function1::class.java)

Answer 2

You can use a parameter function like a factory .

class CustomAdapter<HolderClassGeneric>(val entityFactory: (View,  (Int) -> Unit) -> HolderClassGeneric) : RecyclerView.Adapter<HolderClassGeneric>() {

    /*
    Usual recyclerview stuff
    */ 

    //Method that I want to be called when a list item is clicked
    fun onListItemClicked(position: Int) {
       //do stuff
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): HolderClassGeneric {
        val view = LayoutInflater.from(parent.context).inflate(listItemLayoutResourceId, parent, false)

        val instance = entityFactory(view, this::onListItemClicked)

        return instance

}