java - fragment 中的回收器 View 为空

Question

我正在尝试解析 JSON 数据并使用 RecyclerView 将其显示在 fragment 中。但是，当我运行该应用程序时，我得到一个空白屏幕。我第一次使用 Activity 完成了这段代码，效果非常好。然后我将其转换为 Fragment。在 Fragment 中，它显示一个空白屏幕。

这是我的 fragment 的代码

public class Tab1 extends Fragment {
    private RecyclerView mRecyclerView;
    private ExampleAdapter mExampleAdapter;
    private ArrayList<ExampleItem> mExampleList;
    private RequestQueue mRequestQueue;
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.tab1, container, false);
        mRecyclerView = rootView.findViewById(R.id.recycler_view);
        mRecyclerView.setHasFixedSize(true);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false));
        mExampleList = new ArrayList<>();
        mRequestQueue = Volley.newRequestQueue(requireActivity());
        parseJson();
        return rootView;
    }

    private void parseJson(){
        String url ="http://maranamassapp.cf/json_getdata.php";
        JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null,
                new Response.Listener<JSONObject>() {
                    @Override
                    public void onResponse(JSONObject response) {
                        try {
                            JSONArray jsonArray = response.getJSONArray("server_response");
                            for(int i = 0; i < jsonArray.length(); i++){
                                JSONObject ser =jsonArray.getJSONObject(i);
                                String creatorname =  ser.getString("filmname");
                                String imageUrl = ser.getString("filmimage");
                                String cat = ser.getString("filmcat");

                                mExampleList.add(new ExampleItem(imageUrl,creatorname,cat));
                            }

                            mExampleAdapter = new ExampleAdapter(getContext(),mExampleList);
                            mRecyclerView.setAdapter(mExampleAdapter);
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                error.printStackTrace();
            }
        });

        mRequestQueue.add(request);
    }
}

和适配器代码

public class ExampleAdapter extends RecyclerView.Adapter <ExampleAdapter.ExampleViewHolder>{
    private Context mContext;
    private ArrayList<ExampleItem> mExampleList;
    public ExampleAdapter(Context context, ArrayList<ExampleItem> examplelist){
        mContext =context;
        mExampleList = examplelist;
    }

    @NonNull
    @Override
    public ExampleViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(mContext).inflate(R.layout.example_item,parent,false);
        return new ExampleViewHolder(v);
    }

    @Override
    public void onBindViewHolder(@NonNull ExampleViewHolder holder, int position) {
        ExampleItem currentItem = mExampleList.get(position);
        String imageUrl = currentItem.getmImageUrl();
        String creatorName = currentItem.getmCreator();
        String cat =currentItem.getmCat();

        holder.mTextViewCreator.setText(creatorName);
        holder.mTextViewCat.setText(cat);
        Glide.with(mContext)
                .load(imageUrl)
                .into(holder.mImageView);
    }

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

    public class ExampleViewHolder extends RecyclerView.ViewHolder{
        public ImageView mImageView;
        public TextView mTextViewCreator;
        public TextView mTextViewCat;
        public ExampleViewHolder(View itemView) {
            super(itemView);
            mImageView = itemView.findViewById(R.id.image_view);
            mTextViewCreator = itemView.findViewById(R.id.text_view_creator);
            mTextViewCat = itemView.findViewById(R.id.text_view_cat);
        }
    }
}

有人可以帮忙吗？

Answer 1

我建议您实现如下所示的RecyclerView。

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.tab1, container, false);
    mRecyclerView = rootView.findViewById(R.id.recycler_view);
    mRecyclerView.setHasFixedSize(true);
    mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false));
    mExampleList = new ArrayList<>();
    mRequestQueue = Volley.newRequestQueue(requireActivity());

    // Set the adapter here. 
    // Use getActivity() instead of getContext()
    mExampleAdapter = new ExampleAdapter(getContext(),mExampleList);

    parseJson();
    return rootView;
}

private void parseJson(){
    String url ="http://maranamassapp.cf/json_getdata.php";
    JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    try {
                        JSONArray jsonArray = response.getJSONArray("server_response");
                        for(int i = 0; i < jsonArray.length(); i++){
                            JSONObject ser =jsonArray.getJSONObject(i);
                            String creatorname =  ser.getString("filmname");
                            String imageUrl = ser.getString("filmimage");
                            String cat = ser.getString("filmcat");

                            mExampleList.add(new ExampleItem(imageUrl,creatorname,cat));
                        }

                        // Just call notifyDataSetChanged here 
                        mExampleAdapter.notifyDataSetChanged();

                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            error.printStackTrace();
        }
    });

    mRequestQueue.add(request);
}

请注意，我在 onCreateView 中设置适配器，传递 getActivity() 作为上下文而不是 getContext。在 parseJson 函数中，当使用新添加的数据更新 mExampleList 时，我只是调用 notifyDataSetChanged。

此外，检查您是否正确地从服务器获取响应，并且在解析响应时没有遇到任何异常。

希望这有效!