java - 如何从 RecyclerView Adapter 获取传递给 MainActivity 的变量？

Question

我只是在玩一些代码，学习新东西，当我遇到这个问题时......我试图将一个变量从我的 RecylcerViewAdapter 传递到 MainActivity 中的方法，但我似乎无法完成它。

我尝试了很多不同的界面和转换方法，但没有任何效果。由于我对这一切都很陌生，也许我在某个地方犯了一个小错误？

我的界面:

public interface AdapterCallback {
    void onMethodCallback(int id);
} 

这是我的适配器类:

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

    private List<Post> postList;
    private Context context;
    private AdapterCallback listener;

    public PostAdapter() {
    }

    public PostAdapter(List<Post> postList, Context context) {
        this.postList = postList;
        this.context = context;
    }

    public void setListener(AdapterCallback listener) {
        this.listener = listener;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.recycler_layout, viewGroup, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull final ViewHolder viewHolder, final int position) {
        viewHolder.tvTitle.setText(postList.get(position).getTitle());
        viewHolder.tvBody.setText(new StringBuilder(postList.get(position).getBody().substring(0, 20)).append("..."));
        viewHolder.tvId.setText(String.valueOf(postList.get(position).getUserId()));

        viewHolder.parentLayout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int id = postList.get(position).getId();
                if (listener != null) {
                    listener.onMethodCallback(id);
                }
            }
        });
    }

    @Override
    public int getItemCount() {
        return postList.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {

        TextView tvTitle;
        TextView tvBody;
        TextView tvId;
        LinearLayout parentLayout;

        public ViewHolder(View itemView) {
            super(itemView);

            tvTitle = itemView.findViewById(R.id.tvTitle);
            tvBody = itemView.findViewById(R.id.tvBody);
            tvId = itemView.findViewById(R.id.tvId);
            parentLayout = itemView.findViewById(R.id.parentLayout);
        }
    }
}

And my MainActivity:

public class MainActivity extends AppCompatActivity {

    public static final String TAG = "MainActivityLog";
    private CompositeDisposable disposable = new CompositeDisposable();

    @BindView(R.id.rvPosts)
    RecyclerView rvPosts;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ButterKnife.bind(this);

        rvPosts.setHasFixedSize(true);
        rvPosts.setLayoutManager(new LinearLayoutManager(this));

        populateList();
        logItems();
    }

    private void populateList() {
        MainViewModel viewModel = ViewModelProviders.of(MainActivity.this).get(MainViewModel.class);
        viewModel.makeQuery().observe(MainActivity.this, new Observer<List<Post>>() {
            @Override
            public void onChanged(@Nullable List<Post> posts) {
                PostAdapter adapter = new PostAdapter(posts, getApplicationContext());
                rvPosts.setAdapter(adapter);
            }
        });
    }

    public void logItems() {
        PostAdapter adapter = new PostAdapter();
        adapter.setListener(new AdapterCallback() {
            @Override
            public void onMethodCallback(int id) {
                MainViewModel viewModel = ViewModelProviders.of(MainActivity.this).get(MainViewModel.class);
                viewModel.makeSingleQuery(id).observe(MainActivity.this, new Observer<Post>() {
                    @Override
                    public void onChanged(@Nullable final Post post) {
                        Log.d(TAG, "onChanged: data response");
                        Log.d(TAG, "onChanged: " + post);
                    }
                });
            }
        });
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        disposable.clear();
    }
}

populateList() 方法工作正常，但 logItems() 方法有问题。

因此，当我单击 RecyclerView 中的 View 时，我希望日志输出所单击帖子的标题、描述和 ID。但什么也没发生...

因此，任何帮助将不胜感激。

Answer 1

创建适配器全局变量，即字段。使用相同的对象来设置每个属性。

private PostAdapter adapter;

将您的 logItems 方法替换为:

public void logItems() {
    adapter.setListener(new AdapterCallback() {
        @Override
        public void onMethodCallback(int id) {
            MainViewModel viewModel = ViewModelProviders.of(MainActivity.this).get(MainViewModel.class);
            viewModel.makeSingleQuery(id).observe(MainActivity.this, new Observer<Post>() {
                @Override
                public void onChanged(@Nullable final Post post) {
                    Log.d(TAG, "onChanged: data response");
                    Log.d(TAG, "onChanged: " + post);
                }
            });
        }
    });
}

并用以下内容填充列表:

private void populateList() {
    MainViewModel viewModel = ViewModelProviders.of(MainActivity.this).get(MainViewModel.class);
    viewModel.makeQuery().observe(MainActivity.this, new Observer<List<Post>>() {
        @Override
        public void onChanged(@Nullable List<Post> posts) {
            adapter = new PostAdapter(posts, getApplicationContext());
            rvPosts.setAdapter(adapter);
            logItems();
        }
    });
}

并且不要从 onCreate 调用 logItems()