Android RecyclerView 自定义 OnItemClickListener 崩溃

Question

您好，我正在尝试为我的 RecyclerView 设置一个 onclicklistener，但是当我点击 RecyclerView 中的名称并显示错误代码时它崩溃了：

java.lang.NullPointerException：尝试调用接口方法 '空白 com.motivecodex.githubusers.adapter.RepositoryAdapter$OnItemClickListener.onItemClick(com.motivecodex.githubusers.database.table.Repository)' 在空对象引用上 在 com.motivecodex.githubusers.adapter.RepositoryAdapter$ViewHolder$1.onClick(RepositoryAdapter.java:52)

RepositoryAdapter.java

public class RepositoryAdapter extends RecyclerView.Adapter<RepositoryAdapter.ViewHolder> {

    private static final String LOG_TAG = "RepositoryAdapter";

    public interface OnItemClickListener {
        void onItemClick(Repository repository);
    }

    private List<Repository> repositories;

    private final OnItemClickListener listener;

    public RepositoryAdapter(List<Repository> repositories, OnItemClickListener listener) {
        this.repositories = repositories;
        this.listener = listener;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.listitem_repository, parent, false);

        return new ViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        holder.bind(repositories.get(position), listener);
//        Repository githubRepository = repositories.get(position);
//        holder.name.setText(githubRepository.getName());
//        holder.stars.setText(String.valueOf(githubRepository.getStargazersCount()));
//        holder.forks.setText(String.valueOf(githubRepository.getForksCount()));
    }

    @Override
    public int getItemCount() {
        if (repositories != null) {
            return repositories.size();
        }
        return 0;
    }

    static class ViewHolder extends RecyclerView.ViewHolder {
        private TextView name, stars, forks;

        public ViewHolder(View view) {
            super(view);
            name = (TextView) view.findViewById(R.id.listitem_name);
            stars = (TextView) view.findViewById(R.id.listitem_stars);
            forks = (TextView) view.findViewById(R.id.listitem_forks);
        }

        public void bind(final Repository repository, final OnItemClickListener listener) {
            name.setText(repository.getName());
            stars.setText(String.valueOf(repository.getStargazersCount()));
            forks.setText(String.valueOf(repository.getForksCount()));
            name.setOnClickListener(new View.OnClickListener() {
                @Override public void onClick(View v) {
                    listener.onItemClick(repository);
                    Log.e(LOG_TAG, "Item clicked");
                }
            });
        }
    }
}

MainActivity.java

    mGithubRecyclerView = (RecyclerView) findViewById(R.id.github_repository_recyclerview);
            RecyclerView.LayoutManager mGithubLayoutManager = new LinearLayoutManager(getApplicationContext());
            mGithubRecyclerView.setLayoutManager(mGithubLayoutManager);
            mGithubRecyclerView.setHasFixedSize(true);

....

public void loadRepository(String username) {
        mGithubApi.listRepository(username).enqueue(new Callback<List<Repository>>() {
            @Override
            public void onResponse(Call<List<Repository>> call, Response<List<Repository>> response) {
                mGithubAdapter = new RepositoryAdapter(response.body(), MainActivity.java);
                mGithubRecyclerView.setAdapter(mGithubAdapter);
            }

            @Override
            public void onFailure(Call<List<Repository>> call, Throwable t) {
                Log.e("MainActivity", "error loading from API");
            }
        });
    }

@Override
    public void onItemClick(Repository repository) {
        Log.e(LOG_TAG, "Item clicked");
    }

Answer 1

listener.onItemClick(repository); 是错误的。您传递给 Adapter 的侦听器为 null。

您是否从具有 RecyclerView 的 Activity/Fragment 正确初始化它？

所以，如果你有一个 Activity，它应该是这样的：

public class MyActivity extends AppCompatActivity implements RepositoryAdapter.OnItemClickListener {


     // lots of activity methods


     // called from adapter
     public void onItemClick () {

     }
}

然后，像这样将它传递给您的适配器，

// 'this' is your listener
RepositoryAdapter adapter = new RepoitoryAdapter(context, this);

Answer 2

我会在onBindViewHolder 中使用setOnClickListner。对于onClickListner，您真的不需要RecyclerView 中的接口。 您可以传递一个 Intent 来处理 onClickListner 事件，例如：

@Override
        public void onBindViewHolder(PosterViewHolder holder, final int position) {
// Here pass whatever value you need on the current screen
            final Movies movies = movieItems.get(position);
            String posterUrlPath = movies.getPosterPath();

            Picasso.with(context)
                    .load(Constants.MOVIE_POSTER_URL + posterUrlPath)
                    .placeholder(R.drawable.ic_movies_poster_placeholder)
                    .error(R.drawable.ic_picasso_error)
                    .into(holder.poster);
    // Here is where you get the intent for every properties you need
            holder.itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    Intent intent = new Intent(context, MovieDetailsActivity.class);
                    intent.putExtra(Constants.MOVIE_POSTER, movies.getPosterPath());
                    intent.putExtra(Constants.MOVIE_BACKDROP, movies.getBackdropPath());
                    intent.putExtra(Constants.MOVIE_TITLE, movies.getTitle());
                    intent.putExtra(Constants.MOVIE_OVERVIEW, movies.getOverview());
                    intent.putExtra(Constants.MOVIE_RELEASE_DATE, movies.getReleaseDate());
                    intent.putExtra(Constants.MOVIE_RATINGS, movies.getVoteAverage());
                    context.startActivity(intent);
                }
            });
        }

最后，不要忘记通知任何已注册的观察者数据集已更改。

public void setRepositories(List<Repository> repo) {
    repositories.clear();
    movieItems = repo;
    notifyDataSetChanged();
}

在一个activity或fragment中，你可以如下调用set movies：

adapter.setMovies(movieItems);

在ViewHolder类中分配对象：

public class ViewHolder extends RecyclerView.ViewHolder {

        ImageView poster;

        public PosterViewHolder(View itemView) {
            super(itemView);
            poster = (ImageView) itemView.findViewById(R.id.popular_movies_poster_iv);
        }

    }

希望这会有所帮助！