Kotlin：内部类如何访问在外部类中声明为参数的变量？

Question

我有一个DetailAdapter参数categoryId类型为 的类String。我需要在内部类中访问这个变量DetailHolder。我收到以下错误：

未解决的参考：categoryId

我该如何解决这个问题？

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在您的代码中是一个嵌套类，而不是一个内部类（它在 Java 中的等价物是一个static嵌套类）。

要定义内部类，您需要使用inner关键字：

inner class DetailHolder( ...

这种方式DetailHolder将持有对其封闭类 ( DetailAdapter)的隐式引用，您也将能够访问其属性。

查看有关嵌套和内部类的文档。