1

I have to develop an app for an internship and I'm using AndroidStudio.

For now I'm just trying things and I'm developping a Spank counters app (yeah yeah I know).

I know that there is already a response there : What is a NullPointerException, and how do I fix it? and many other questions similar to mine. The fact is I understant the error but I can't find it in my code.

(I havn't put the xml file because I don't think it's usefull bet let me konw if you want to see it.)

Sorry if it's hard to read this post. It's the first time I ask something on a forum. Thanks in advance for those who will be brave enough to read it and help me.

So here is errors :

                                                                          --------- beginning of crash
06-02 18:05:31.515 2680-2680/com.example.florian.fessee E/AndroidRuntime: FATAL EXCEPTION: main
                                                                          Process: com.example.florian.fessee, PID: 2680
                                                                          java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.florian.fessee/com.example.florian.fessee.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2236)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
                                                                              at android.app.ActivityThread.access$800(ActivityThread.java:151)
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                              at android.os.Looper.loop(Looper.java:135)
                                                                              at android.app.ActivityThread.main(ActivityThread.java:5254)
                                                                              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:903)
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
                                                                           Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
                                                                              at android.content.ContextWrapper.getPackageName(ContextWrapper.java:132)
                                                                              at android.preference.PreferenceManager.getDefaultSharedPreferencesName(PreferenceManager.java:374)
                                                                              at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:369)
                                                                              at com.example.florian.fessee.MainActivity.<init>(MainActivity.java:23)
                                                                              at java.lang.reflect.Constructor.newInstance(Native Method)
                                                                              at java.lang.Class.newInstance(Class.java:1606)
                                                                              at android.app.Instrumentation.newActivity(Instrumentation.java:1066)
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2226)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
                                                                              at android.app.ActivityThread.access$800(ActivityThread.java:151) 
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                              at android.os.Looper.loop(Looper.java:135) 
                                                                              at android.app.ActivityThread.main(ActivityThread.java:5254) 
                                                                              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:903) 
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
06-02 18:11:28.569 3101-3101/com.example.florian.fessee D/AndroidRuntime: Shutting down VM
06-02 18:11:28.570 3101-3101/com.example.florian.fessee E/AndroidRuntime: FATAL EXCEPTION: main
                                                                          Process: com.example.florian.fessee, PID: 3101
                                                                          java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.florian.fessee/com.example.florian.fessee.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2236)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
                                                                              at android.app.ActivityThread.access$800(ActivityThread.java:151)
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                              at android.os.Looper.loop(Looper.java:135)
                                                                              at android.app.ActivityThread.main(ActivityThread.java:5254)
                                                                              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:903)
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
                                                                           Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
                                                                              at android.content.ContextWrapper.getPackageName(ContextWrapper.java:132)
                                                                              at android.preference.PreferenceManager.getDefaultSharedPreferencesName(PreferenceManager.java:374)
                                                                              at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:369)
                                                                              at com.example.florian.fessee.MainActivity.<init>(MainActivity.java:23)
                                                                              at java.lang.reflect.Constructor.newInstance(Native Method)
                                                                              at java.lang.Class.newInstance(Class.java:1606)
                                                                              at android.app.Instrumentation.newActivity(Instrumentation.java:1066)
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2226)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
                                                                              at android.app.ActivityThread.access$800(ActivityThread.java:151) 
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                              at android.os.Looper.loop(Looper.java:135) 
                                                                              at android.app.ActivityThread.main(ActivityThread.java:5254) 
                                                                              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:903) 
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
06-02 18:16:53.409 3339-3339/com.example.florian.fessee D/AndroidRuntime: Shutting down VM
06-02 18:16:53.435 3339-3339/com.example.florian.fessee E/AndroidRuntime: FATAL EXCEPTION: main
                                                                          Process: com.example.florian.fessee, PID: 3339
                                                                          java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.florian.fessee/com.example.florian.fessee.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2236)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
                                                                              at android.app.ActivityThread.access$800(ActivityThread.java:151)
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                              at android.os.Looper.loop(Looper.java:135)
                                                                              at android.app.ActivityThread.main(ActivityThread.java:5254)
                                                                              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:903)
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
                                                                           Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
                                                                              at android.content.ContextWrapper.getPackageName(ContextWrapper.java:132)
                                                                              at android.preference.PreferenceManager.getDefaultSharedPreferencesName(PreferenceManager.java:374)
                                                                              at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:369)
                                                                              at com.example.florian.fessee.MainActivity.<init>(MainActivity.java:23)
                                                                              at java.lang.reflect.Constructor.newInstance(Native Method)
                                                                              at java.lang.Class.newInstance(Class.java:1606)
                                                                              at android.app.Instrumentation.newActivity(Instrumentation.java:1066)
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2226)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
                                                                              at android.app.ActivityThread.access$800(ActivityThread.java:151) 
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                              at android.os.Looper.loop(Looper.java:135) 
                                                                              at android.app.ActivityThread.main(ActivityThread.java:5254) 
                                                                              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:903) 
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
06-02 18:19:42.932 3515-3515/com.example.florian.fessee D/AndroidRuntime: Shutting down VM
06-02 18:19:42.935 3515-3515/com.example.florian.fessee E/AndroidRuntime: FATAL EXCEPTION: main
                                                                          Process: com.example.florian.fessee, PID: 3515
                                                                          java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.florian.fessee/com.example.florian.fessee.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2236)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
                                                                              at android.app.ActivityThread.access$800(ActivityThread.java:151)
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                              at android.os.Looper.loop(Looper.java:135)
                                                                              at android.app.ActivityThread.main(ActivityThread.java:5254)
                                                                              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:903)
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
                                                                           Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
                                                                              at android.content.ContextWrapper.getPackageName(ContextWrapper.java:132)
                                                                              at android.preference.PreferenceManager.getDefaultSharedPreferencesName(PreferenceManager.java:374)
                                                                              at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:369)
                                                                              at com.example.florian.fessee.MainActivity.<init>(MainActivity.java:23)
                                                                              at java.lang.reflect.Constructor.newInstance(Native Method)
                                                                              at java.lang.Class.newInstance(Class.java:1606)
                                                                              at android.app.Instrumentation.newActivity(Instrumentation.java:1066)
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2226)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
                                                                              at android.app.ActivityThread.access$800(ActivityThread.java:151) 
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                              at android.os.Looper.loop(Looper.java:135) 
                                                                              at android.app.ActivityThread.main(ActivityThread.java:5254) 
                                                                              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:903) 
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 

And here is my code :

package com.example.florian.fessee;

import android.content.SharedPreferences;
import android.preference.PreferenceManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    private int compt = 0;
    private Button b1 = null;
    private Button b5 = null;
    private Button b01 = null;
    private Button b05 = null;
    private Button braz = null;
    private TextView t = null;
    private String COMPT = "comptfess";

    SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
    SharedPreferences.Editor editor = preferences.edit();

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

        b1 = (Button) findViewById(R.id.button1);
        b5 = (Button) findViewById(R.id.button5);
        b01 = (Button) findViewById(R.id.button01);
        b05 = (Button) findViewById(R.id.button05);
        braz = (Button) findViewById(R.id.buttonraz);

        t = (TextView) findViewById(R.id.textView);

        compt = preferences.getInt(COMPT, 0);

        b1.setOnClickListener(b1Listener);
        b5.setOnClickListener(b5Listener);
        b01.setOnClickListener(b01Listener);
        b05.setOnClickListener(b05Listener);
        braz.setOnClickListener(brazListener);

        if (compt == 1) {
            t.setText("Je dois 1 fessée à Sophie.");
        }
        else if (compt!=0){
            t.setText("Je dois " + compt + "fessées à Sophie.");
        }

    }

    private View.OnClickListener b1Listener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            compt +=1;

            editor.putInt(COMPT,compt);
            editor.commit();

            if (compt == 1) {
                t.setText("Je dois 1 fessée à Sophie.");
            }
            else if (compt!=0){
                t.setText("Je dois " + compt + "fessées à Sophie.");
            }
        }
    };

    private View.OnClickListener b5Listener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            compt +=5;

            editor.putInt(COMPT,compt);
            editor.commit();

            if (compt == 1) {
                t.setText("Je dois 1 fessée à Sophie.");
            }
            else if (compt!=0){
                t.setText("Je dois " + compt + "fessées à Sophie.");
            }
        }
    };

    private View.OnClickListener b01Listener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(compt!=0){
                compt -=1;

                editor.putInt(COMPT,compt);
                editor.commit();

                if (compt==0){
                    t.setText("Je ne dois plus de fessées å Sophie");
                }

                else if (compt == 1) {
                    t.setText("Je dois 1 fessée à Sophie.");
                }
                else{
                    t.setText("Je dois " + compt + "fessées à Sophie.");
                }

            }
            else {
                Toast.makeText(MainActivity.this, "Un nombre de fessées doit être positif.", Toast.LENGTH_SHORT).show();
            }
        }
    };

    private View.OnClickListener b05Listener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(compt>4){
                compt -=5;

                editor.putInt(COMPT,compt);
                editor.commit();

                if (compt==0){
                    t.setText("Je ne dois plus de fessées å Sophie.");
                }

                else if (compt == 1) {
                    t.setText("Je dois 1 fessée à Sophie.");
                }
                else{
                    t.setText("Je dois " + compt + "fessées à Sophie.");
                }

            }
            else {
                Toast.makeText(MainActivity.this, "Un nombre de fessées doit être positif.", Toast.LENGTH_SHORT).show();
            }
        }
    };

    private View.OnClickListener brazListener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            compt = 0;
            editor.putInt(COMPT,compt);
            editor.commit();
            t.setText("Je ne dois plus de fessées à Sophie.");
        }
    };
}
Community
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Beuhbounnet
  • 13
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  • In order to find the errors easier, a suggested read is this post. http://stackoverflow.com/questions/3988788/what-is-a-stack-trace-and-how-can-i-use-it-to-debug-my-application-errors – OneCricketeer Jun 02 '16 at 17:50
  • Follow up to that comment, your stacktrace has `at com.example.florian.fessee.MainActivity.(MainActivity.java:23)` which points you to the problematic code – OneCricketeer Jun 02 '16 at 17:51
  • For anyone tempted to complain about the error message formatting, somehow the SO editor is really choking on some aspect of it - multiple attempts at cleanup have not worked. – Chris Stratton Jun 02 '16 at 17:55

2 Answers2

2

It seems your argument boils down to the idea that passing an Activity Context to getDefaultSharedPreferences() should be valid.

And normally it should - but only after the Activity's Context is fully initialized. I believe that is only true during or after the call to onCreate().

You can declare your preferences related variables where you are, but don't attempt to initialize them until during or after onCreate().

Chris Stratton
  • 39,853
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  • 117
2

This is your problem:

    SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
    SharedPreferences.Editor editor = preferences.edit();

You can't initialize SharedPreferences before the Activity has been created. Separate your declaration and instantiation like this:

...

SharedPreferences preferences;
SharedPreferences.Editor editor;

...

@Override
public void onCreate(Bundle savedInstanceState){

    ...

    preferences = PreferenceManager.getDefaultSharedPreferences(this);
    editor = preferences.edit();

    ...

}
RScottCarson
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