Kotlin：内部类如何访问在外部类中声明为参数的变量？

Question

I have a DetailAdapter class with a parameter categoryId of type String . I need access to this variable in the inner class DetailHolder . I get the following error:

Unresolved reference: categoryId

How can I solve this?

class DetailAdapter(lifecycleOwner: LifecycleOwner, categoryId: String) : FirebaseRecyclerAdapter<Detail, DetailAdapter.DetailHolder>(DetailAdapter.buildOptions(lifecycleOwner, categoryId)) {

companion object {
    private fun buildQuery(categoryId: String) = FirebaseDatabase.getInstance()
            .reference
            .child("").child("details").child(categoryId)
            .limitToLast(50)

    private fun buildOptions(lifecycleOwner: LifecycleOwner, categoryId: String) = FirebaseRecyclerOptions.Builder<Detail>()
            .setQuery(buildQuery(categoryId), Detail::class.java)
            .setLifecycleOwner(lifecycleOwner)
            .build()
}

class DetailHolder(val customView: View, var detail: Detail? = null) : RecyclerView.ViewHolder(customView) {
    private val TAG = DetailHolder::class.java.simpleName

    fun bind(detail: Detail) {
        with(detail) {
            customView.textView_name?.text = detail.detailName
            customView.textView_description?.text = detail.detailDescription

            val detailId = detail.detailId

            customView.setOnClickListener {
                    // do something
            }

            customView.setOnLongClickListener(
                    {
                        showDeleteDetailDialog(it, categoryId, detailId)
                        true
                    }
            )
        }
    }

Answer 1

DetailHolder in your code is a nested class, not an inner one (its equivalent in Java would be a static nested class).

To define an inner class you need to use the inner keyword:

inner class DetailHolder( ...

This way DetailHolder will hold an implicit reference to its enclosing class ( DetailAdapter ) and you'll be able to access its properties as well.

Check out the documentation on Nested and Inner Classes .