java - onBindViewHolder(RecyclerView.ViewHolderholder, intposition) - 无法访问holder的 'fun' - Kotlin到Java

Question

我有 2 个 RecyclerView 类 - Adapter 和 ViewHolder。 在用 Kotlin 编写的 Adapter 类中，我正在实现 onBindViewHolder(RecyclerView.ViewHolderholder, intposition) 方法，并且我能够访问 holder.bind() - fun - 很容易，但是当我尝试将这个 Kotlin 文件重新制作为 Java 文件并访问 holder.bind() 时，这是不可能的。如何从 Java 文件访问 holder.bind()？

class RepoViewHolder(view: View) : RecyclerView.ViewHolder(view) {
private val name: TextView = view.findViewById(R.id.repo_name)
private val description: TextView = view.findViewById(R.id.repo_description)
private val stars: TextView = view.findViewById(R.id.repo_stars)
private val language: TextView = view.findViewById(R.id.repo_language)
private val forks: TextView = view.findViewById(R.id.repo_forks)

private var repo: Repo? = null

init {
    view.setOnClickListener {
        repo?.url?.let { url ->
            val intent = Intent(Intent.ACTION_VIEW, Uri.parse(url))
            view.context.startActivity(intent)
        }
    }
}

fun bind(repo: Repo?) {
    if (repo == null) {
        val resources = itemView.resources
        name.text = resources.getString(R.string.loading)
        description.visibility = View.GONE
        language.visibility = View.GONE
        stars.text = resources.getString(R.string.unknown)
        forks.text = resources.getString(R.string.unknown)
    } else {
        showRepoData(repo)
    }
}

private fun showRepoData(repo: Repo) {
    this.repo = repo
    name.text = repo.fullName

    // if the description is missing, hide the TextView
    var descriptionVisibility = View.GONE
    if (repo.description != null) {
        description.text = repo.description
        descriptionVisibility = View.VISIBLE
    }
    description.visibility = descriptionVisibility

    stars.text = repo.stars.toString()
    forks.text = repo.forks.toString()

    // if the language is missing, hide the label and the value
    var languageVisibility = View.GONE
    if (!repo.language.isNullOrEmpty()) {
        val resources = this.itemView.context.resources
        language.text = resources.getString(R.string.language, repo.language)
        languageVisibility = View.VISIBLE
    }
    language.visibility = languageVisibility
}

companion object {
    fun create(parent: ViewGroup): RepoViewHolder {
        val view = LayoutInflater.from(parent.context)
                .inflate(R.layout.repo_view_item, parent, false)
        return RepoViewHolder(view)
    }
}}

Kotlin 适配器文件:

class ReposAdapter : ListAdapter<Repo, RecyclerView.ViewHolder>(REPO_COMPARATOR) {

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
    return RepoViewHolder.create(parent)
}

override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
    val repoItem = getItem(position)
    if (repoItem != null) {
        (holder as RepoViewHolder).bind(repoItem)
    }
}

companion object {
    private val REPO_COMPARATOR = object : DiffUtil.ItemCallback<Repo>() {
        override fun areItemsTheSame(oldItem: Repo, newItem: Repo): Boolean =
                oldItem.fullName == newItem.fullName

        override fun areContentsTheSame(oldItem: Repo, newItem: Repo): Boolean =
                oldItem == newItem
    }
}}

这是我的 Java 文件，我正在尝试将 Kotlin 的适配器转换为 Java:

public class ReposAdapterJava extends ListAdapter<Repo, RecyclerView.ViewHolder> {

private static DiffUtil.ItemCallback<Repo> callback = new DiffUtil.ItemCallback<Repo>() {
    @Override
    public boolean areItemsTheSame(Repo oldItem, Repo newItem) {
        return oldItem.getFullName().equals(newItem.getFullName());
    }

    @Override
    public boolean areContentsTheSame(Repo oldItem, Repo newItem) {
        return oldItem == newItem;
    }
};

protected ReposAdapterJava() {
    super(callback);
}

@NonNull
@Override
public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    return RepoViewHolder.Companion.create(parent);
}

@Override
public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
    Repo itemRepo = getItem(position);
    if(itemRepo != null){
        holder.bind(itemRepo) // not possible
    }
}}

这些代码 fragment 来自 Android Paging Codelab。

Answer 1

替换

if(itemRepo != null){
   holder.bind(itemRepo) // not possible
}

与

if (itemRepo != null && holder instanceof RepoViewHolder) {
   ((RepoViewHolder) holder).bind(itemRepo)
}

使用当前代码，它无法访问，因为在 onBindViewHolder 处，您引用了 RecyclerView.ViewHolder(Base Calss)，它无法访问子类的属性。