Showing Error :Attempt to invoke interface method 'int java.util.List.size()' on a null object reference

Question

I'm creating an app that display contact list in a listview.The problem is I'm getting the following error when I run my app and I'm struggling to fix it:

04-05 13:41:48.868 2488-2488/? E/AndroidRuntime: FATAL EXCEPTION: main
                                             Process: com.kksworld.jsonparsing, PID: 2488
                                             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.kksworld.jsonparsing.MainActivity$JSONTask.onPostExecute(MainActivity.java:120)
                                                 at com.kksworld.jsonparsing.MainActivity$JSONTask.onPostExecute(MainActivity.java:48)
                                                 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)

Here is my code :

MainActivity.java

package com.kksworld.jsonparsing;
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.ListView;
import android.widget.TextView;
import com.kksworld.jsonparsing.models.ContactModel;
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 listView;

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

    listView = (ListView)findViewById(R.id.lvContacts)
    }


public class JSONTask extends AsyncTask<String,String,List<ContactModel>>{

    @Override
    protected List<ContactModel> doInBackground(String... params) {

        HttpURLConnection httpURLConnection = null;
        BufferedReader bufferedReader = null;

        try {
            URL url = new URL(params[0]);
            httpURLConnection = (HttpURLConnection) url.openConnection();
            httpURLConnection.connect();
            InputStream inputStream = httpURLConnection.getInputStream();
            // Through this we can read the data line by line
            bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            StringBuffer stringBuffer = new StringBuffer();
            String line = "";
            while ((line = bufferedReader.readLine()) != null) {
                stringBuffer.append(line);
            }

            String finalJSON = stringBuffer.toString();
            JSONArray mainArray = new JSONArray(finalJSON);
            JSONObject parentObject = mainArray.getJSONObject(0);
            JSONArray parentArray = parentObject.getJSONArray("contacts");

            List<ContactModel> contactModelList = new ArrayList<>();

            // For parsing a list of items you have to use for loop
            for(int i=0;i<11;i++) {
                JSONObject finalObject = parentArray.getJSONObject(i);
                ContactModel contactModel = new ContactModel();
                contactModel.setName(finalObject.getString("name"));
                contactModel.setPhone(finalObject.getString("phone"));
                contactModel.setEmail(finalObject.getString(("email")));
                contactModel.setOfficePhone(finalObject.getString(("officePhone")));
                contactModel.setLatitude((float) finalObject.getDouble("latitude"));
                contactModel.setLongitude((float) finalObject.getDouble("longitude"));
                // Adding the finalObject in the List
                contactModelList.add(contactModel);

            }
            return contactModelList;

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        } finally {
            if (httpURLConnection != null) {
                httpURLConnection.disconnect();
                try {
                    if (bufferedReader != null) {
                        bufferedReader.close();
                    }
                }catch(IOException e){
                    e.printStackTrace();
                }
            }
        }
        return null;
    }

    // Value returned by doInBackGround will be passed here...

    @Override
    protected void onPostExecute(List<ContactModel> result) {
        super.onPostExecute(result);

        ContactAdapter contactAdapter = new ContactAdapter(getApplicationContext(),R.layout.row,result);
        listView.setAdapter(contactAdapter);
    }
}

public class ContactAdapter extends ArrayAdapter{

    private List<ContactModel> contactModelList;
    private int resource;
    private LayoutInflater inflater;

    public ContactAdapter(Context context, int resource, List<ContactModel> objects) {
        super(context, resource, objects);
        contactModelList=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);
        }
        TextView textViewName;
        TextView textViewEmail;
        TextView textViewPhone;
        TextView textViewOfficePhone;

        textViewName = (TextView)convertView.findViewById(R.id.textViewInsertName);
        textViewEmail= (TextView)convertView.findViewById(R.id.textViewInsertEmail);
        textViewPhone= (TextView)convertView.findViewById(R.id.textViewInsertPhone);
        textViewOfficePhone = (TextView)convertView.findViewById(R.id.textViewInsertOfficeNumber);

        textViewName.setText(contactModelList.get(position).getName());
        textViewEmail.setText(contactModelList.get(position).getEmail());
        textViewPhone.setText(contactModelList.get(position).getPhone());
        textViewOfficePhone.setText(contactModelList.get(position).getOfficePhone());

        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("some_url");
        return true;
    }

    return super.onOptionsItemSelected(item);
}

}

Could someone please help.

My guess is the response from your HTTP call is not parsing as JSON, probably hitting a JSONException in your AsyncTask, which causes your task to return null...which you then feed to your ContactAdapter and triggers the NullPointerException. — Robert Nekic
– Robert Nekic, Commented Apr 5, 2016 at 18:24
any chance contactModelList being passed from doInBackground() to onPostExecute() is null? — ben_joseph
– ben_joseph, Commented Apr 5, 2016 at 18:25
The exact explanation of how you are getting NullPointerException at ArrayAdapter.getCount() can be found here. stackoverflow.com/questions/36212453/… — Shadab Ansari
– Shadab Ansari, Commented Apr 5, 2016 at 18:37

Dmitri Timofti · Accepted Answer · 2016-04-05 18:27:27Z

25

Extract this line

List<ContactModel> contactModelList = new ArrayList<>();

before the try block and instead of return null; use return contactModelList;

Looks like your parsing fails and you pass a null object to onPostExecute().

answered Apr 5, 2016 at 18:27

Dmitri Timofti

2,4181 gold badge24 silver badges25 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Robin Davies · Accepted Answer · 2016-04-05 18:24:18Z

2

The List object which you passed into the adapter is null. So when the adapter calls list.Size(), a null pointer exception is thrown.

Use a debugger, set a breakpoint somewhere around com.kksworld.jsonparsing.MainActivity$JSONTask.onPostExecute(MainActivity.java:48), and work your way backward from there if you can't figure it out.

One assumes that your json parse failed somehow or another.

answered Apr 5, 2016 at 18:24

Robin Davies

7,9551 gold badge43 silver badges56 bronze badges

Comments

Kottur · Accepted Answer · 2023-02-13 12:52:52Z

1

Perhaps someone else will look for an answer. This method also works as error prevention

public int getItemCount() {
        if(list==null) return 0;
        return list.size();
    }

edited Feb 13, 2023 at 12:52

answered Feb 13, 2023 at 12:52

Kottur

112 bronze badges

Comments

Vit · Accepted Answer · 2018-11-02 19:57:08Z

0

I was building similar app from youtube video and I've got same error, but I saw also error "Cleartext HTTP traffic not allowed to site.com", so I found solution android:usesCleartextTraffic="true" here Android 8: Cleartext HTTP traffic not permitted and it solved all problems without modifying MainActivity. Btw, on API 16 it wasn't showing errors.

answered Nov 2, 2018 at 19:57

Vit

4882 gold badges9 silver badges20 bronze badges

Collectives™ on Stack Overflow

Showing Error :Attempt to invoke interface method 'int java.util.List.size()' on a null object reference

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related