从片段中的json获取值
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【中文标题】从片段中的json获取值【英文标题】：Get values from json in fragment 【发布时间】：2021-07-06 21:35:36 【问题描述】：我正在尝试从 JSON 获取信息到卡片视图中，我已经在一个单独的项目中制作了这个应用程序并且它可以工作，但现在我正在尝试将它与实际应用程序集成。我正在为实际应用程序使用片段。
package com.example.loginfirebase.news;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonArrayRequest;
import com.android.volley.toolbox.Volley;
import com.example.loginfirebase.R;
import com.google.android.gms.common.api.Response;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;
public class NewsFragment extends Fragment
RecyclerView recyclerView;
List<Anunturi> anunturiLi;
private static String JSON_URL = "";
Adapter adapter;
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
public NewsFragment()
// Required empty public constructor
public static NewsFragment newInstance(String param1, String param2)
NewsFragment fragment = new NewsFragment();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
@Override
public void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
if(container==null)
Log.v("Container",": Containerul este null");
// Inflate the layout for this fragment
Context aplicationcontext = getActivity().getApplicationContext();
//Context thiscontext = container.getContext();
RecyclerView recyclerView=container.findViewById(R.id.anunturiList);
if (recyclerView==null)
Log.v("recycler view value","is null");
Context fragmentcontext=container.getContext();
anunturiLi = new ArrayList<>();
extractAnunturi(aplicationcontext,fragmentcontext);
Log.v("Aplication context", String.valueOf(aplicationcontext));
return inflater.inflate(R.layout.fragment_news, container, false);
// public void onViewCreated(View view, Bundle savedInstanceState)
// super.onCreate(savedInstanceState);
// RecyclerView recyclerView=view.findViewById(R.id.anunturiList);
//
//
//
private void extractAnunturi(Context aplicationcontext,Context fragmentcontext)
//TODO: FIX
Context mContext;
mContext = fragmentcontext;
Log.v("Activity non null","activity:"+getActivity());
RequestQueue queue = Volley.newRequestQueue(getActivity());
JsonArrayRequest jsonArrayRequest = new JsonArrayRequest(Request.Method.GET, JSON_URL, null, new com.android.volley.Response.Listener<JSONArray>()
@Override
public void onResponse(JSONArray response)
for (int i = 0; i < response.length(); i++)
try
JSONObject anunturiObject = response.getJSONObject(i);
Anunturi anunturi = new Anunturi();
anunturi.setTitle(anunturiObject.getString("titlu_anunt"));
Log.v("Tag anunturi title:",anunturi.getTitle());
anunturi.setAutor(anunturiObject.getString("autor_anunt".toString()));
Log.v("Tag anunturi title:",anunturi.getAutor());
anunturi.setCoverImage(anunturiObject.getString("cover_image"));
Log.v("Tag anunturi title:",anunturi.getCoverImage());
anunturi.setAnuntURL(anunturiObject.getString("url"));
Log.v("Tag anunturi title:",anunturi.getAnuntURL());
anunturi.setText_anunt(anunturiObject.getString("text_anunt"));
Log.v("Tag anunturi title:",anunturi.getText_anunt());
anunturiLi.add(anunturi);
catch (JSONException e)
e.printStackTrace();
//TODO FIX
recyclerView.setLayoutManager(new LinearLayoutManager(getApplicationContext()));
adapter = new Adapter(getApplicationContext(), anunturiLi);
recyclerView.setAdapter(adapter);
, new com.android.volley.Response.ErrorListener()
@Override
public void onErrorResponse(VolleyError error)
//nimic
);
queue.add(jsonArrayRequest);
我得到了这个错误
F:\LoginFirebase\app\src\main\java\com\example\loginfirebase\news\NewsFragment.java:127: error: cannot find symbol
recyclerView.setLayoutManager(new LinearLayoutManager(getApplicationContext()));
^
symbol: method getApplicationContext()
我尝试将上下文作为参数传递并更改为：
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity().getApplicationContext()));
adapter = new Adapter(getActivity().getApplicationContext(), anunturiLi);
recyclerView.setAdapter(adapter);
但我得到了这个错误
2021-04-11 19:37:42.632 26960-26960/com.example.loginfirebase D/AndroidRuntime: Shutting down VM
2021-04-11 19:37:42.633 26960-26960/com.example.loginfirebase E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.loginfirebase, PID: 26960
java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager)' on a null object reference
at com.example.loginfirebase.news.NewsFragment$1.onResponse(NewsFragment.java:127)
at com.example.loginfirebase.news.NewsFragment$1.onResponse(NewsFragment.java:103)
at com.android.volley.toolbox.JsonRequest.deliverResponse(JsonRequest.java:90)
at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:102)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
适配器代码：
package com.example.loginfirebase.news;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.example.loginfirebase.R;
import com.squareup.picasso.Picasso;
import java.util.List;
public class Adapter extends RecyclerView.Adapter<Adapter.ViewHolder>
LayoutInflater inflater;
List<Anunturi> anunturi;
public Adapter(Context ctx, List<Anunturi> anunturi)
this.inflater= LayoutInflater.from(ctx);
this.anunturi=anunturi;
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType)
View view=inflater.inflate(R.layout.custom_list_layout,parent,false);
return new ViewHolder(view);
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position)
//bind the data
holder.titlu_anunt.setText(anunturi.get(position).getTitle());
holder.autor_anunt.setText(anunturi.get(position).getAutor());
Picasso.get().load(anunturi.get(position).getCoverImage()).into(holder.img_anunt);
holder.text_anunt.setText(anunturi.get(position).getText_anunt());
@Override
public int getItemCount()
return anunturi.size();
public class ViewHolder extends RecyclerView.ViewHolder
TextView titlu_anunt,autor_anunt,text_anunt;
ImageView img_anunt;
public ViewHolder(@NonNull View itemView)
super(itemView);
titlu_anunt=itemView.findViewById(R.id.anunt_title);
autor_anunt=itemView.findViewById(R.id.anunt_autor);
text_anunt=itemView.findViewById(R.id.txt_anunt);
img_anunt=itemView.findViewById(R.id.anunt_image);
解决方案
必须将代码放在 onViewCreated 中
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState)
super.onViewCreated(view, savedInstanceState);
RecyclerView recyclerView=view.findViewById(R.id.anunturiList);
//View view = inflater.inflate(R.layout.fragment_news, container, false);
anunturiLi = new ArrayList<>();
extractAnunturi();
【问题讨论】：
尝试在 Fragment 的onAttach() 方法中初始化变量 aplicationcontext。
【参考方案1】：
当你这样做时：
RecyclerView recyclerView=container.findViewById(R.id.anunturiList);
您将 Recycler View 分配给一个局部变量，因此您的 recyclerView 字段仍然为空。当你在下面使用它时，它会导致 NPE。
您必须将其分配给recyclerView 字段：
recyclerView=container.findViewById(R.id.anunturiList);
【讨论】：
将分配更改为您建议的内容，我仍然收到相同的错误，在我 setLayoutmanager 的行中可以使用 getActivity().getApplicationContext() 吗？以上是关于从片段中的json获取值的主要内容，如果未能解决你的问题，请参考以下文章
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