我希望有人能帮我解决我的问题。我有一个有 3 个选项卡的 android 应用程序，我使用 fragment ，第一个选项卡是 recyclerView 列表，第二个选项卡是 map 。问题出在选项卡 1 中，我需要使用 volley 获取数据到选项卡 1 上的 recyclerView，如果运行正常但我无法在第一个应用程序启动时看到数据，但是当我更改选项卡并再次返回选项卡 1 时，它将刷新数据并在 recyclerView 上显示数据。

适配器.java

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

    private Context context;
    private List<Warkop> mWarkop;
    private LayoutInflater inflater;


    public CustomListAdapterWarkop(Context context, List<Warkop> mWarkop) {
        this.context=context;
        inflater= LayoutInflater.from(context);
        this.mWarkop = mWarkop;
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = inflater.inflate(R.layout.list_warkop_row, parent, false);
        ItemViewHolder holder = new ItemViewHolder(view);

        return holder;
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        ItemViewHolder viewHolder = (ItemViewHolder) holder;
        Warkop current = mWarkop.get(position);

        viewHolder.tvNamaWarkop.setText(current.getNamaWarkop());


        ImageLoader imageLoader = ImageLoader.getInstance();
        DisplayImageOptions options = new DisplayImageOptions.Builder().cacheInMemory(true)
                .cacheOnDisc(true).resetViewBeforeLoading(true)
                .showImageForEmptyUri(R.drawable.noimage)
                .showImageOnFail(R.drawable.noimage)
                .showImageOnLoading(R.drawable.noimage).build();
        imageLoader.displayImage(current.getFotoWarkop(), viewHolder.ivFotoWarkop, options);

    }

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

}

ItemHolder.java

package com.andylah.warkopedia;

import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;

/**
 * Created by andylah on 11/3/2017.
 */

public class ItemViewHolder extends RecyclerView.ViewHolder {

    public ImageView ivFotoWarkop;
    public TextView tvNamaWarkop;

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

        tvNamaWarkop = itemView.findViewById(R.id.nama_warkop);
        ivFotoWarkop = itemView.findViewById(R.id.image_warkop);

    }
}

标签1.java

public class tabSatu extends Fragment {

    private static final String TAG = tabDua.class.getSimpleName();
    public static final int CONNECTION_TIMEOUT = 10000;
    public static final int READ_TIMEOUT = 15000;
    private boolean isFragmentLoaded = false;
    View vTabSatu;
    private RecyclerView recyclerView;
    public static List<Warkop> warkopList = new ArrayList<Warkop>();
    private CustomListAdapterWarkop warkopAdapter;

    public tabSatu(){

    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    }

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

        new AsyncFetch().execute();

        vTabSatu = inflater.inflate(R.layout.tabsatu_view, container, false);

        recyclerView = vTabSatu.findViewById(R.id.warkop_container);

        LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());

        recyclerView.setLayoutManager(layoutManager);

        Log.d("LOG : ", "onCreatedView Run");

        // Inflate the layout for this fragment
        return vTabSatu;
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        warkopAdapter = new CustomListAdapterWarkop(getActivity(), warkopList);

        warkopAdapter.notifyDataSetChanged();

        recyclerView.setAdapter(warkopAdapter);

        Log.d("LOG : ", "onViewCreated Run");
    }

    @Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
        if (isVisibleToUser && !isFragmentLoaded ) {
            // Load your data here or do network operations here
            isFragmentLoaded = true;
            //new AsyncFetch().execute();
        }else{
            isFragmentLoaded = false;


            Log.d("LOG : ", "isFragmentLoaded = false");
        }
    }

    private class AsyncFetch extends AsyncTask<String, String, String> {

        ProgressDialog pDialog = new ProgressDialog(getActivity());

        HttpURLConnection conn;
        URL url = null;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();

            pDialog.setMessage("Loading list warkop ...");
            pDialog.setCancelable(false);
            pDialog.show();
        }

        @Override
        protected String doInBackground(String... strings) {
            try {

                // Enter URL address where your json file resides
                // Even you can make call to php file which returns json data
                url = new URL(AppConfig.LOAD_WARKOP);

            } catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
                return e.toString();
            }
            try {

                // Setup HttpURLConnection class to send and receive data from php and mysql
                conn = (HttpURLConnection) url.openConnection();
                conn.setReadTimeout(READ_TIMEOUT);
                conn.setConnectTimeout(CONNECTION_TIMEOUT);
                conn.setRequestMethod("POST");

                // setDoOutput to true as we recieve data from json file
                conn.setDoOutput(true);

            } catch (IOException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
                return e1.toString();
            }
            try {

                int response_code = conn.getResponseCode();

                // Check if successful connection made
                if (response_code == HttpURLConnection.HTTP_OK) {

                    // Read data sent from server
                    InputStream input = conn.getInputStream();
                    BufferedReader reader = new BufferedReader(new InputStreamReader(input));
                    StringBuilder result = new StringBuilder();
                    String line;

                    while ((line = reader.readLine()) != null) {
                        result.append(line);
                    }

                    // Pass data to onPostExecute method
                    return (result.toString());

                } else {

                    return ("unsuccessful");
                }

            } catch (IOException e) {
                e.printStackTrace();
                return e.toString();
            } finally {
                conn.disconnect();
            }
        }

        @Override
        protected void onPostExecute(String result) {
            pDialog.dismiss();

            try{
                JSONObject object = new JSONObject(result);
                String getObject = object.getString("warkop");
                JSONArray jsonArray = new JSONArray(getObject);
                boolean error = object.getBoolean("error");

                if(!error){
                    for (int i = 0; i < jsonArray.length(); i++) {
                        JSONObject jsonObject = jsonArray.getJSONObject(i);

                        Warkop warkop = new Warkop();

                        warkop.setNamaWarkop(jsonObject.getString("nama_warkop"));
                        warkop.setAlamatWrkop(jsonObject.getString("alamat_warkop"));
                        warkop.setKotaWarkop(jsonObject.getString("kota_warkop"));
                        warkop.setLatWarkop(Double.parseDouble(jsonObject.getString("lat_warkop")));
                        warkop.setLangWarkop(Double.parseDouble(jsonObject.getString("long_warkop")));
                        warkop.setIsWifi(Integer.parseInt(jsonObject.getString("is_wifi")));
                        warkop.setIsToilet(Integer.parseInt(jsonObject.getString("is_toilet")));
                        warkop.setIsTv(Integer.parseInt(jsonObject.getString("is_tv")));
                        warkop.setIsColokan(Integer.parseInt(jsonObject.getString("is_colokan")));
                        warkop.setIsParkir(Integer.parseInt(jsonObject.getString("is_parkir")));
                        warkop.setFotoWarkop(jsonObject.getString("foto_warkop"));

                        warkopList.add(warkop);
                    }
                }else{
                    String errorMsg = object.getString("error_msg");
                    Toast.makeText(getContext(),
                            errorMsg, Toast.LENGTH_LONG).show();
                }

            }catch (JSONException e) {

                e.printStackTrace();
                Toast.makeText(getActivity(), "Json error: " + e.getMessage(), Toast.LENGTH_LONG).show();
            }

        }
    }

}

最佳答案

问题:即使您调用 notifyDataSetChanged()，但 Adapter 中没有数据。

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    warkopAdapter = new CustomListAdapterWarkop(getActivity(), warkopList);
    warkopAdapter.notifyDataSetChanged();
    recyclerView.setAdapter(warkopAdapter);
}

因此需要在API调用后设置warkopList并通知给Adapter。它会帮助你。

标签状态:

    @Override
    protected void onPostExecute(String result) {
        pDialog.dismiss();

        try {
          JSONObject object = new JSONObject(result);
          String getObject = object.getString("warkop");
          JSONArray jsonArray = new JSONArray(getObject);
          boolean error = object.getBoolean("error");

          if (!error) {
            for (int i = 0; i < jsonArray.length(); i++) {
              JSONObject jsonObject = jsonArray.getJSONObject(i);

              Warkop warkop = new Warkop();

              ...

              warkopList.add(warkop);
              adapter.setItems(warkopList);
            }
          }
          ...
        }

CustomListAdapterWarkop: 添加setItem()方法到适配器

public class CustomListAdapterWarkop extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
    ...
    public void setItems(List<WarkopList> warkopList) {
      mWarkop = warkopList;
      notifyDataSetChanged();
    }
    ...
  }

关于android - Fragment、Volley 和 RecyclerView，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/47128561/