Null pointer exception: invoking virtual method
Question
i am trying to design a basic chat app. The app is build without any errors but as soon as i click any button on the emulator the app crashes and the log shows the following error:
07-01 22:50:39.367 30016-30032/com.example.ibm_admin.chat E/Buffer Error﹕ Error converting result java.lang.NullPointerException: lock == null
07-01 22:50:39.367 30016-30032/com.example.ibm_admin.chat E/JSON Parser﹕ Error parsing data org.json.JSONException: End of input at character 0 of
07-01 22:50:39.370 30016-30016/com.example.ibm_admin.chat D/AndroidRuntime﹕ Shutting down VM
07-01 22:50:39.370 30016-30016/com.example.ibm_admin.chat E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.ibm_admin.chat, PID: 30016
java.lang.NullPointerException: Attempt to invoke virtual method 'int org.json.JSONArray.length()' on a null object reference
at com.example.ibm_admin.chat.UserFragment$Load.onPostExecute(UserFragment.java:84)
at com.example.ibm_admin.chat.UserFragment$Load.onPostExecute(UserFragment.java:71)
at android.os.AsyncTask.finish(AsyncTask.java:632)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
07-01 22:50:40.975 30016-30023/com.example.ibm_admin.chat W/art﹕ Suspending all threads took: 15.530ms
07-01 22:51:02.766 30016-30023/com.example.ibm_admin.chat W/art﹕ Suspending all threads took: 6.893ms
MainActivity.java
import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentTransaction;
import android.content.Context;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.Toast;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.gcm.GoogleCloudMessaging;
import java.io.IOException;
public class MainActivity extends Activity {
private final static int PLAY_SERVICES_RESOLUTION_REQUEST = 9000;
String SENDER_ID = "Your Project Number";
static final String TAG = "L2C";
GoogleCloudMessaging gcm;
SharedPreferences prefs;
Context context;
String regid;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
prefs = getSharedPreferences("Chat", 0);
context = getApplicationContext();
if(!prefs.getString("REG_FROM","").isEmpty()){
Fragment user = new UserFragment();
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, user);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack(null);
ft.commit();
}else if(!prefs.getString("REG_ID", "").isEmpty()){
Fragment reg = new LoginFragment();
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, reg);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack(null);
ft.commit();
}else if(checkPlayServices()){
new Register().execute();
}else{
Toast.makeText(getApplicationContext(),"This device is not supported",Toast.LENGTH_SHORT).show();
}
}
private boolean checkPlayServices() {
int resultCode = GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);
if (resultCode != ConnectionResult.SUCCESS) {
if (GooglePlayServicesUtil.isUserRecoverableError(resultCode)) {
GooglePlayServicesUtil.getErrorDialog(resultCode, this,
PLAY_SERVICES_RESOLUTION_REQUEST).show();
} else {
Log.i(TAG, "This device is not supported.");
finish();
}
return false;
}
return true;
}
private class Register extends AsyncTask<String, String, String> {
@Override
protected String doInBackground(String... args) {
try {
if (gcm == null) {
gcm = GoogleCloudMessaging.getInstance(context);
regid = gcm.register(SENDER_ID);
Log.e("RegId",regid);
SharedPreferences.Editor edit = prefs.edit();
edit.putString("REG_ID", regid);
edit.commit();
}
return regid;
} catch (IOException ex) {
Log.e("Error", ex.getMessage());
return "Fails";
}
}
@Override
protected void onPostExecute(String json) {
Fragment reg = new LoginFragment();
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, reg);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack(null);
ft.commit();
}
}
}
JSONParser.java
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.util.Log;
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static JSONArray jAry = null;
static String json = "";
// constructor
public JSONParser() {
}
public JSONObject getJSONFromUrl(String url,List<NameValuePair> params) {
// Making HTTP request
try {
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
if(params != null){
httpPost.setEntity(new UrlEncodedFormEntity(params));
}
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "n");
}
is.close();
json = sb.toString();
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
}
// try parse the string to a JSON object
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jObj;
}
public JSONArray getJSONArray(String url,List<NameValuePair> params) {
// Making HTTP request
try {
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "n");
}
is.close();
json = sb.toString();
Log.e("JSS",json);
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
}
// try parse the string to a JSON object
try {
jAry = new JSONArray(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jAry;
}
}
LoginFragment.java
import android.app.Fragment;
import android.app.FragmentTransaction;
import android.app.ProgressDialog;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;
public class LoginFragment extends Fragment {
SharedPreferences prefs;
EditText name, mobno;
Button login;
List<NameValuePair> params;
ProgressDialog progress;
@Override
public View onCreateView(LayoutInflater inflater,ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.login_fragment, container, false);
prefs = getActivity().getSharedPreferences("Chat", 0);
name = (EditText)view.findViewById(R.id.name);
mobno = (EditText)view.findViewById(R.id.mobno);
login = (Button)view.findViewById(R.id.log_btn);
progress = new ProgressDialog(getActivity());
progress.setMessage("Registering ...");
progress.setProgressStyle(ProgressDialog.STYLE_SPINNER);
progress.setIndeterminate(true);
login.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
progress.show();
SharedPreferences.Editor edit = prefs.edit();
edit.putString("REG_FROM", mobno.getText().toString());
edit.putString("FROM_NAME", name.getText().toString());
edit.commit();
new Login().execute();
}
});
return view;
}
private class Login extends AsyncTask<String, String, JSONObject> {
@Override
protected JSONObject doInBackground(String... args) {
JSONParser json = new JSONParser();
params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("name", name.getText().toString()));
params.add(new BasicNameValuePair("mobno", mobno.getText().toString()));
params.add((new BasicNameValuePair("reg_id",prefs.getString("REG_ID",""))));
JSONObject jObj = json.getJSONFromUrl("http://10.0.2.2:8080/login",params);
return jObj;
}
@Override
protected void onPostExecute(JSONObject json) {
progress.dismiss();
try {
String res = json.getString("response");
if(res.equals("Sucessfully Registered")) {
Fragment reg = new UserFragment();
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, reg);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack(null);
ft.commit();
}else{
Toast.makeText(getActivity(),res,Toast.LENGTH_SHORT).show();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}
}
UserFragment.java
import android.app.Fragment;
import android.app.FragmentTransaction;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
public class UserFragment extends Fragment {
ListView list;
ArrayList<HashMap<String, String>> users = new ArrayList<HashMap<String, String>>();
Button refresh,logout;
List<NameValuePair> params;
SharedPreferences prefs;
@Override
public View onCreateView(LayoutInflater inflater,ViewGroup container, Bundle savedInstanceState) {
View view =inflater.inflate(R.layout.user_fragment, container, false);
prefs = getActivity().getSharedPreferences("Chat", 0);
list = (ListView)view.findViewById(R.id.listView);
refresh = (Button)view.findViewById(R.id.refresh);
logout = (Button)view.findViewById(R.id.logout);
logout.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
new Logout().execute();
}
});
refresh.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
getFragmentManager().beginTransaction().remove(getFragmentManager().findFragmentById(R.id.content_frame)).commit();
Fragment reg = new UserFragment();
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, reg);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack(null);
ft.commit();
}
});
new Load().execute();
return view;
}
private class Load extends AsyncTask<String, String, JSONArray> {
@Override
protected JSONArray doInBackground(String... args) {
JSONParser json = new JSONParser();
params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("mobno", prefs.getString("REG_FROM","")));
JSONArray jAry = json.getJSONArray("http://10.0.2.2:8080/getuser",params);
return jAry;
}
@Override
protected void onPostExecute(JSONArray json) {
for(int i = 0; i < json.length(); i++){
JSONObject c = null;
try {
c = json.getJSONObject(i);
String name = c.getString("name");
String mobno = c.getString("mobno");
HashMap<String, String> map = new HashMap<String, String>();
map.put("name", name);
map.put("mobno", mobno);
users.add(map);
} catch (JSONException e) {
e.printStackTrace();
}
}
ListAdapter adapter = new SimpleAdapter(getActivity(), users,
R.layout.user_list_single,
new String[] { "name","mobno" }, new int[] {
R.id.name, R.id.mobno});
list.setAdapter(adapter);
list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
Bundle args = new Bundle();
args.putString("mobno", users.get(position).get("mobno"));
Intent chat = new Intent(getActivity(), ChatActivity.class);
chat.putExtra("INFO", args);
startActivity(chat);
}
});
}
}
private class Logout extends AsyncTask<String, String, JSONObject> {
@Override
protected JSONObject doInBackground(String... args) {
JSONParser json = new JSONParser();
params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("mobno", prefs.getString("REG_FROM","")));
JSONObject jObj = json.getJSONFromUrl("http://10.0.2.2:8080/logout",params);
return jObj;
}
@Override
protected void onPostExecute(JSONObject json) {
String res = null;
try {
res = json.getString("response");
Toast.makeText(getActivity(),res,Toast.LENGTH_SHORT).show();
if(res.equals("Removed Sucessfully")) {
Fragment reg = new LoginFragment();
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, reg);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack(null);
ft.commit();
SharedPreferences.Editor edit = prefs.edit();
edit.putString("REG_FROM", "");
edit.commit();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}
}
ChatActivity.java
import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.SharedPreferences;
import android.graphics.Color;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.content.LocalBroadcastManager;
import android.text.Html;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TableLayout;
import android.widget.TableRow;
import android.widget.TextView;
import android.widget.Toast;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;
public class ChatActivity extends Activity {
SharedPreferences prefs;
List<NameValuePair> params;
EditText chat_msg;
Button send_btn;
Bundle bundle;
TableLayout tab;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_chat);
tab = (TableLayout)findViewById(R.id.tab);
prefs = getSharedPreferences("Chat", 0);
bundle = getIntent().getBundleExtra("INFO");
SharedPreferences.Editor edit = prefs.edit();
edit.putString("CURRENT_ACTIVE", bundle.getString("mobno"));
edit.commit();
LocalBroadcastManager.getInstance(this).registerReceiver(onNotice, new IntentFilter("Msg"));
if(bundle.getString("name") != null){
TableRow tr1 = new TableRow(getApplicationContext());
tr1.setLayoutParams(new TableRow.LayoutParams( TableRow.LayoutParams.WRAP_CONTENT, TableRow.LayoutParams.WRAP_CONTENT));
TextView textview = new TextView(getApplicationContext());
textview.setTextSize(20);
textview.setTextColor(Color.parseColor("#0B0719"));
textview.setText(Html.fromHtml("<b>"+bundle.getString("name")+" : </b>"+bundle.getString("msg")));
tr1.addView(textview);
tab.addView(tr1);
}
chat_msg = (EditText)findViewById(R.id.chat_msg);
send_btn = (Button)findViewById(R.id.sendbtn);
send_btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
TableRow tr2 = new TableRow(getApplicationContext());
tr2.setLayoutParams(new TableRow.LayoutParams( TableRow.LayoutParams.WRAP_CONTENT, TableRow.LayoutParams.WRAP_CONTENT));
TextView textview = new TextView(getApplicationContext());
textview.setTextSize(20);
textview.setTextColor(Color.parseColor("#A901DB"));
textview.setText(Html.fromHtml("<b>You : </b>" + chat_msg.getText().toString()));
tr2.addView(textview);
tab.addView(tr2);
new Send().execute();
}
});
}
private BroadcastReceiver onNotice= new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
String str = intent.getStringExtra("msg");
String str1 = intent.getStringExtra("fromname");
String str2 = intent.getStringExtra("fromu");
if(str2.equals(bundle.getString("mobno"))){
TableRow tr1 = new TableRow(getApplicationContext());
tr1.setLayoutParams(new TableRow.LayoutParams( TableRow.LayoutParams.WRAP_CONTENT, TableRow.LayoutParams.WRAP_CONTENT));
TextView textview = new TextView(getApplicationContext());
textview.setTextSize(20);
textview.setTextColor(Color.parseColor("#0B0719"));
textview.setText(Html.fromHtml("<b>"+str1+" : </b>"+str));
tr1.addView(textview);
tab.addView(tr1);
}
}
};
private class Send extends AsyncTask<String, String, JSONObject> {
@Override
protected JSONObject doInBackground(String... args) {
JSONParser json = new JSONParser();
params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("from", prefs.getString("REG_FROM","")));
params.add(new BasicNameValuePair("fromn", prefs.getString("FROM_NAME","")));
params.add(new BasicNameValuePair("to", bundle.getString("mobno")));
params.add((new BasicNameValuePair("msg",chat_msg.getText().toString())));
JSONObject jObj = json.getJSONFromUrl("http://10.0.2.2:8080/send",params);
return jObj;
}
@Override
protected void onPostExecute(JSONObject json) {
chat_msg.setText("");
String res = null;
try {
res = json.getString("response");
if(res.equals("Failure")){
Toast.makeText(getApplicationContext(),"The user has logged out. You cant send message anymore !",Toast.LENGTH_SHORT).show();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}
}
Please can someone help me?
3 answers
solution1
1 ACCPTED 2015-07-01 18:49:13
This:
java.lang.NullPointerException: Attempt to invoke virtual method 'int org.json.JSONArray.length()' on a null object reference
at com.example.ibm_admin.chat.UserFragment$Load.onPostExecute(UserFragment.java:84)
means, that in file UserFragment.java at line 84 in inner class Load of class com.example.ibm_admin.chat.UserFragment there is method length was called on some object, which is null.
I suppose, that is this line:
for(int i = 0; i < json.length(); i++){
in this method parameter json equals null .
Probably, in your doInBackroung method, jObj.getJSONArray returns null .
It is hard to know what exactly happened, because your JSONParser.getJSONArray suppresses all the exceptions and returns null, if any.
Look at next two lines of logcat:
07-01 22:50:39.367 30016-30032/com.example.ibm_admin.chat E/Buffer Error﹕ Error converting result java.lang.NullPointerException: lock == null
07-01 22:50:39.367 30016-30032/com.example.ibm_admin.chat E/JSON Parser﹕ Error parsing data org.json.JSONException: End of input at character 0 of
That's means somewhere inside that block in getJSONArray you have a null reference, that probably comes from topmost part of getJSONArray where other exceptions was suppressed, and is variable become null .
You have to carefully debug through all the code.
solution2
0 2015-07-02 07:38:20
This is the exception you are getting mainly
java.lang.NullPointerException: Attempt to invoke virtual method 'int org.json.JSONArray.length()' on a null object reference
at com.example.ibm_admin.chat.UserFragment$Load.onPostExecute(UserFragment.java:84)
To check the array is empty or not this is better before parsing.Like this
JSONArray dataArray = new JSONArray(data);
if(!(dataArray.length() == 0)){
for(int i = 0 ;i < dataArray.length();i++){
JSONObject chainObj = dataArray.getJSONObject(i);
String chain_name = chainObj.getString("chain_name");
String chain_id = chainObj.getString("retailerid");
String chain_location = chainObj.getString("area");
}
}
solution3
-1 2015-07-01 18:51:08
this is retrun null JSONArray jAry = json.getJSONArray(" http://10.0.2.2:8080/getuser ",params); in userFragment due to server response is not valid json and when you are call json.length(). json object is null UserFragment$Load.onPostExecute(Jsonarray json).
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