nullPointerException with button onclick listener

Question

i'm having nullPointerException issue that i can't resolve. could someone help please?

my code:

package gsb.com;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.widget.TextView;

the main class

public class ActivitePrincipale extends Activity {
    //Variables pour l'authentification
        private TextView tv;
        public static final int RESULT_Main = 1;

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

            //Authentification
            //Appel de la page de Login 
            startActivityForResult(new Intent(ActivitePrincipale.this, Login.class), RESULT_Main);
            //tv = new TextView(this);
            //setContentView(tv);
        }

        //Procédure d'authentification
        private void startup(Intent i) 
        {
            // Récupère l'identifiant        
            int user = i.getIntExtra("userid",-1);

            //Affiche les identifiants de l'utilisateur
            tv.setText("UserID: "+String.valueOf(user)+" logged in");
        }

        protected void onActivityResult(int requestCode, int resultCode, Intent data) 
        { 
            if(requestCode == RESULT_Main && resultCode == RESULT_CANCELED)  
                finish(); 
            else 
                startup(data);
        }


}

the login class

package gsb.com;
import gsb.com.R;


import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.protocol.HTTP;
import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.Bundle;
import android.os.Looper;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class Login extends Activity
{
    // Lien vers votre page php sur le serveur
    private static final String UPDATE_URL  = some ip
    public ProgressDialog progressDialog;
    private EditText UserEditText;
    private EditText PassEditText;
    private android.widget.Button button;

    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        Log.i("Info","Dans Login - onCreate --------------");
        //initialisation d'une progress bar
        progressDialog = new ProgressDialog(this);
        progressDialog.setMessage("Patientez svp...");
        progressDialog.setIndeterminate(true);
        progressDialog.setCancelable(false);

        //recuperation des elements de la vue
        UserEditText = (EditText)findViewById(R.id.username);
        if (UserEditText == null) { Log.w("Info", "UserEditText est null --------------"); }
        PassEditText = (EditText)findViewById(R.id.password);
        if (PassEditText == null) { Log.w("Info", "PassEditText est null --------------"); }
        button = (Button)findViewById(R.id.okbutton);
        if (button == null) { Log.w("Info", "button est null --------------"); }

        //definition du listener du bouton ok
        button.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {

                int userSize = UserEditText.getText().length();
                int passSize = PassEditText.getText().length();

                //si les deux champs sont complétés
                if(userSize > 0 && passSize > 0){
                    progressDialog.show();
                    String user = UserEditText.getText().toString();
                    String pass = PassEditText.getText().toString();
                    //appel de la fonction doLogin qui va appeler le script connect.php
                    doLogin(user,pass);
                }
                else {
                    createDialog("Erreur !!", "SVP Entrez un nom d'utilisateur et un mot de passe.");
                }
            }
        });

        button = (Button)findViewById(R.id.cancelbutton);
        //creation du listener du bouton annuler pour sortir de l'appli
        button.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {

                quit(false, null);
            }
        });
    }

    private void quit(boolean succes, Intent i){
        //envoi d'un resultat qui va permettre de quitter l'appli
        setResult((succes)? Activity.RESULT_OK : Activity.RESULT_CANCELED,i);
        finish();
    }

    private void createDialog(String title, String text){
        //affichage d'un popup
        AlertDialog ad  = new AlertDialog.Builder(this)
                .setPositiveButton("Ok", null).setTitle(title).setMessage(text)
                .create();
        ad.show();
    }

    private void doLogin(final String login, final String pass){
        final String pw = md5(pass);
        //final String pw = pass;

        //creation d'un thread
        Thread t = new Thread(){
            public void run(){
                Looper.prepare();
                //connexion au serveur pour communiquer avec le php
                DefaultHttpClient client = new DefaultHttpClient();
                HttpConnectionParams.setConnectionTimeout(client.getParams(),15000);

                HttpResponse response;
                HttpEntity entity;

                try{
                    //on etablit un lien avec le script connect.php
                    HttpPost post = new HttpPost(UPDATE_URL);
                    List<NameValuePair> nvp = new ArrayList<NameValuePair>();
                    nvp.add(new BasicNameValuePair("username",login));
                    nvp.add(new BasicNameValuePair("password",pw));
                    post.setHeader("Content-Type", "application/x-www-form-urlencoded");

                    //passage des params login et password qui vont etre recup par le script php en Post
                    post.setEntity(new UrlEncodedFormEntity(nvp, HTTP.UTF_8));

                    //recup du resultat du script
                    response = client.execute(post);
                    entity = response.getEntity();
                    InputStream is = entity.getContent();

                    //appel d'une fonction pour traduire la reponse
                    read(is);
                    is.close();

                    if(entity != null){
                        entity.consumeContent();
                    }
                }
                catch(Exception e){
                    progressDialog.dismiss();
                    createDialog("Error", "Impossible d'etablir une connexion");
                }
                Looper.loop();
            }
        };
        t.start();
    }

    private void read(InputStream inpStr){
        //traduction du resultat du flux
        SAXParserFactory spf = SAXParserFactory.newInstance();
        SAXParser sp;

        try{
            sp = spf.newSAXParser();
            XMLReader xr = sp.getXMLReader();

            //classe definie plus bas
            LoginContentHandler lch = new LoginContentHandler();

            xr.setContentHandler(lch);
            xr.parse(new InputSource(inpStr));          
        }
        catch(ParserConfigurationException e){}
        catch(SAXException e){}
        catch(IOException e){}
    }

    private String md5(String in) {

        MessageDigest digest;

        try {

            digest = MessageDigest.getInstance("MD5");

            digest.reset();

            digest.update(in.getBytes());

            byte[] a = digest.digest();

            int len = a.length;

            StringBuilder sb = new StringBuilder(len << 1);

            for (int i = 0; i < len; i++) {
                sb.append(Character.forDigit((a[i] & 0xf0) >> 4, 16));
                sb.append(Character.forDigit(a[i] & 0x0f, 16));
            }

            return sb.toString();

        }
        catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }

        return null;
    }

    private class LoginContentHandler extends DefaultHandler {
        //Traite le retour du script connect.php

        private boolean in_loginTag = false;
        private int userID;
        private boolean error_occured = false;

        public void startElement(String n, String l, String q, Attributes a) throws SAXException {

                if(l=="login"){
                    in_loginTag = true;
                }

                if(l=="error"){
                    progressDialog.dismiss();

                    switch(Integer.parseInt(a.getValue("value"))){
                    case 1:
                        createDialog("Error", "Impossible de se connecter à la base de données");
                        break;
                    case 2:
                        createDialog("Error", "Erreur dans la base de données, Table manquante");
                        break;
                    case 3:
                        createDialog("Error", "Login ou mot de passe invalide !");
                        break;
                    }
                    error_occured = true;
                }

                if(l=="user" && in_loginTag && a.getValue("id")!=""){
                    //si tout est ok on recup l'id de l'utilisateur
                    userID = Integer.parseInt(a.getValue("id"));
                }                           
        }

        public void endElement(String n, String l, String q) throws SAXException {
            //on renvoie l'id si tout est ok
            if(l=="login"){
                in_loginTag = false;

                if(! error_occured){
                    progressDialog.dismiss();
                    Intent i = new Intent();
                    i.putExtra("userid", userID);
                    quit(true, i);
                }
            }
        }

        public void characters(char ch[], int start, int length){}
        public void startDocument() throws SAXException{}
        public void endDocument() throws SAXException{}
    }
}

the xml files

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".ActivitePrincipale" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="14dp"
        android:text="@string/connexion_form_title" />

    <EditText
        android:id="@+id/password"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/username"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="25dp"
        android:ems="10"
        android:inputType="textPassword"
        android:text="@string/password_text_field"/>

    <EditText
        android:id="@+id/username"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView1"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="34dp"
        android:inputType="text"
        android:ems="10" 
        android:text="@string/username_text_field"/>

    <Button
        android:id="@+id/okbutton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/password"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="66dp"
        android:text="@string/connexion_button" />

    <Button
        android:id="@+id/cancelbutton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/okbutton"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="30dp"
        android:text="@string/cancel_button" />

</RelativeLayout>

the manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="gsb.com"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="17" />

<uses-permission android:name="android.permission.INTERNET"></uses-permission>

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="gsb.com.ActivitePrincipale"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name="gsb.com.Login" android:label="Login">

            <intent-filter>

                <action android:name="android.intent.action.VIEW" />

                <category android:name="android.intent.category.DEFAULT" />

            </intent-filter>

        </activity>
    </application>    

</manifest>

and the error logs

    05-30 13:29:37.252: I/Info(712): Dans Login - onCreate --------------
    05-30 13:29:37.272: W/Info(712): UserEditText est null --------------
    05-30 13:29:37.272: W/Info(712): PassEditText est null --------------
    05-30 13:29:37.282: W/Info(712): button est null --------------
    05-30 13:29:37.304: D/AndroidRuntime(712): Shutting down VM
    05-30 13:29:37.304: W/dalvikvm(712): threadid=1: thread exiting with uncaught exception (group=0x40015560)
    05-30 13:29:37.342: E/AndroidRuntime(712): FATAL EXCEPTION: main
    05-30 13:29:37.342: E/AndroidRuntime(712): java.lang.RuntimeException: Unable to start activity ComponentInfo{gsb.com/gsb.com.Login}: java.lang.NullPointerException
    05-30 13:29:37.342: E/AndroidRuntime(712):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at android.os.Handler.dispatchMessage(Handler.java:99)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at android.os.Looper.loop(Looper.java:123)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at android.app.ActivityThread.main(ActivityThread.java:3683)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at java.lang.reflect.Method.invokeNative(Native Method)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at java.lang.reflect.Method.invoke(Method.java:507)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at dalvik.system.NativeStart.main(Native Method)
    05-30 13:29:37.342: E/AndroidRuntime(712): Caused by: java.lang.NullPointerException
    05-30 13:29:37.342: E/AndroidRuntime(712):  at gsb.com.Login.onCreate(Login.java:67)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
    05-30 13:29:37.342: E/AndroidRuntime(712):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
    05-30 13:29:37.342: E/AndroidRuntime(712):  ... 11 more

it seems that some did have issues with the button listener but reading the posts did not give me the solution i expected. thanks for your help.

Could UserEditText or PassEditText be null, perhaps? Just set a breakpoint on the first line of your listener and step through in the debugger. — Phil Haigh
– Phil Haigh, Commented May 30, 2013 at 13:50
Please accept one of the answers that worked for you to show your appreciation and so it may help others with the same question — codeMagic
– codeMagic, Commented May 30, 2013 at 14:18

Sandeep P · Accepted Answer · 2013-05-30 13:52:31Z

5

you have to first use setContentview(R.layout.XXXX) after super, then only you can use resource. other wise you will get the null pointer exception .. set content view is missing in in Login Activity....

edited May 30, 2013 at 13:52

answered May 30, 2013 at 13:47

Sandeep P

4,4212 gold badges28 silver badges46 bronze badges

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Comments

TronicZomB · Accepted Answer · 2013-05-30 17:38:10Z

You are trying to set the same button variable to two different buttons on your layout:

button = (Button)findViewById(R.id.okbutton);
button = (Button)findViewById(R.id.cancelbutton);

You need to create two separate variables for these.

EDIT After much debate, I tried some code again and realized where the issue was.

I had set the Buttons as follows:

button = (Button) findViewById(R.id.ok);
button = (Button) findViewById(R.id.cancel);

button.setOnClickListener(new View.OnClickListener() {
     public void onClick(View v){
         //stuff
     }
});

button.setOnClickListener(new View.OnClickListener() {
     public void onClick(View v){
         // other stuff
     }
});

THIS WILL NOT WORK!!! However after much debate I thought to try something else as follows:

button = (Button) findViewById(R.id.ok);
button.setOnClickListener(new View.OnClickListener() {
     public void onClick(View v){
         //stuff
     }
});

button = (Button) findViewById(R.id.cancel);
button.setOnClickListener(new View.OnClickListener() {
     public void onClick(View v){
         // other stuff
     }
});

This on the other hand DOES work.

Community · Accepted Answer · 2017-05-23 11:46:25Z

2

Your problem here, or at least one is that you don't inflate a layout in Login. So any View you try to use (BUtton, EditText, etc...) will be null

In onCreate() call setContentView(R.layout.yourLayout); BEFORE trying to set Views like

UserEditText = (EditText)findViewById(R.id.username);

The Views exist inside the Layout so they are null until after you have inflated the layout using an inflater or by calling setContentView(...);

Also, just a couple things about the site since you are new

Please read the FAQ
When posting code, please pick out the parts that you think are most relevant and post those along with a relevant logcat and error messages. We will kindly ask for more if needed
If you post multiple classes, please separate them instead of one long section so it is easier for members to read
All of the import statements typically aren't necessary

These aren't really a problem but will help you to get better/quicker answers.

edited May 23, 2017 at 11:46

CommunityBot

11 silver badge

answered May 30, 2013 at 13:47

codeMagic

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5 Comments

fred Over a year ago

OK thanks for your comments. the line 67 is the one in Login class

fred Over a year ago

whith button.setOnclickListener

codeMagic Over a year ago

Because you haven't called setContentView() as in my answer

codeMagic Over a year ago

The Button is null so when you try to set a listener or call a function on it you get NPE

codeMagic Over a year ago

No problem, I saw that so I was just giving you suggestions for next time. Its all about learning. Anyway, you should have an xml file for your login page. Set that before initializing any Views

a_schimpf · Accepted Answer · 2013-05-30 13:54:41Z

1

I notice you have no setContentView in your Login activity. Usually, people get null-pointer errors with findViewById(...), if they call it before calling setContentView. In your case, you don't even have setContentView().

answered May 30, 2013 at 13:54

a_schimpf

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1 Comment

fred Over a year ago

Thanks ! it works now. really helpfull. as I said, I'm really new in java programming. big up!

Phil Haigh · Accepted Answer · 2013-05-30 14:47:24Z

0

If your OK button is not responding to clicks, it is possible that the listener instance is being swept up by the garbage collector.

Create your listeners as class level properties:

private OnClickListener okListener = new View.OnClickListener() { ... };
private OnClickListener cancelListener = new View.OnClickListener() { ... };

Then assign them in onCreate():

((Button)findViewById(R.id.okbutton)).setOnClickListener(okListener);
((Button)findViewById(R.id.cancelbutton)).setOnClickListener(cancelListener );

As the listeners have references inside the activity, they'll not get garbage collected. I had a similar problem starting a media player on a separate thread. The player got killed because I didn't hold on to a reference to the thread, so the garbage collector saw an unreferenced object tree and cleaned it away.

answered May 30, 2013 at 14:47

Phil Haigh

4,5911 gold badge27 silver badges30 bronze badges

2 Comments

TronicZomB Over a year ago

How are single methods garbage collected within the active activity? That doesn't make sense. The reason your thread was garbage collected was because it is separate from the activity and wasn't linked to it. Have you tried this code? Didn't seem to work for me...

fred Over a year ago

this code is not over yet but I wanted to try it first in emulator and have been crashed down on apk start. it's ok now, thanks !

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