I am trying to display JSON data, in a ListView, that I have parsed but I get the following error when I try to run the app.
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
Here is the stack trace.
05-14 22:06:30.169 14034-14034/com.example.jsonparsing_v2 E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.jsonparsing_v2, PID: 14034
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:337)
at android.widget.ListView.setAdapter(ListView.java:491)
at com.example.jsonparsing_v2.MainActivity$JSONTask.onPostExecute(MainActivity.java:131)
at com.example.jsonparsing_v2.MainActivity$JSONTask.onPostExecute(MainActivity.java:49)
at android.os.AsyncTask.finish(AsyncTask.java:651)
at android.os.AsyncTask.-wrap1(AsyncTask.java)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
My code.
package com.example.jsonparsing_v2;
import android.content.Context;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import com.example.jsonparsing_v2.models.ArticleModel;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private ListView lvArticles;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
lvArticles = (ListView)findViewById(R.id.lvArticles);
}
public class JSONTask extends AsyncTask<String,String,List<ArticleModel>>{
@Override
protected List<ArticleModel> doInBackground(String... params) {
HttpURLConnection connection = null;
BufferedReader reader = null;
try {
URL url = new URL(params[0]);
connection =(HttpURLConnection) url.openConnection();
connection.connect();
InputStream stream = connection.getInputStream();
reader = new BufferedReader(new InputStreamReader(stream));
StringBuffer buffer = new StringBuffer();
String line = "";
while ((line = reader.readLine())!= null){
buffer.append(line);
}
String finalJson = buffer.toString();
JSONObject parentObject = new JSONObject(finalJson);
JSONArray parentArray = parentObject.getJSONArray("");
List<ArticleModel> articleModelList = new ArrayList<>();
for (int i=0;i<parentArray.length(); i++) {
JSONObject finalObject = parentArray.getJSONObject(i);
ArticleModel articleModel = new ArticleModel();
articleModel.setId(finalObject.getString("id"));
articleModel.setSectionId(finalObject.getString("sectionId"));
articleModel.setWebPublicationDate(finalObject.getInt("webPublicationDate"));
articleModel.setWebTitle(finalObject.getString("webTitle"));
articleModel.setWebUrl(finalObject.getString("webUrl"));
articleModel.setApiUrl(finalObject.getString("apiUrl"));
articleModel.setSectionName(finalObject.getString("sectionName"));
articleModel.setHeadline(finalObject.getString("headline"));
articleModel.setThumbnail(finalObject.getString("thumbnail"));
// adding the final object in the list
articleModelList.add(articleModel);
}
return articleModelList;
}
catch(MalformedURLException e) {
e.printStackTrace();
}
catch (IOException e){
e.printStackTrace();
} catch (JSONException e) {
e.printStackTrace();
} finally{
if (connection != null){
connection.disconnect();
}
try {
if (reader != null){
reader.close();
}
}
catch (IOException e){
e.printStackTrace();
}
}
return null;
}
@Override
protected void onPostExecute(List<ArticleModel> result) {
super.onPostExecute(result);
ArticleAdapter adapter = new ArticleAdapter(getApplicationContext(), R.layout.row, result);
lvArticles.setAdapter(adapter);
}
}
public class ArticleAdapter extends ArrayAdapter{
private List<ArticleModel> articleModelList;
private int resource;
private LayoutInflater inflater;
public ArticleAdapter(Context context, int resource, List<ArticleModel> objects) {
super(context, resource, objects);
articleModelList = objects;
this.resource = resource;
inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if(convertView == null){
convertView = inflater.inflate(resource, null);
}
ImageView ivArticleIcon;
TextView tvDate;
TextView tvSummary;
ivArticleIcon = (ImageView) convertView.findViewById(R.id.ivIcon);
tvDate = (TextView) convertView.findViewById(R.id.tvDate);
tvSummary = (TextView) convertView.findViewById(R.id.tvSummary);
tvDate.setText(articleModelList.get(position).getWebPublicationDate()+":");
tvSummary.setText(articleModelList.get(position).getHeadline());
return convertView;
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_refresh) {
new JSONTask().execute("http://public.ocito.com/m/test/guardian.html");
return true;
}
return super.onOptionsItemSelected(item);
}
}
