Getting a nullpointerexception here for things I don't understand

Question

EDIT: I moved everything to OnCreateView as you guys said but now I get the errors that "my listView is non-static field cannot be referenced to static (same for getApplication()" and that "ArrayAdapter cant be resolved as constructor"

So I want to make a listView in my activity with fragment and I implemented the following code from a tutorial. It doesn't show me where the error is and I don't know exactly which object or thing is null.

package com.example.aland.intrigueme;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;


public class listActivity extends ActionBarActivity {


    ListView listView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list);
        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment())
                    .commit();
        }

        //haal listView van XML
        listView = (ListView) findViewById(R.id.list);

        //waarden in Array definiëren om lijst te tonen

        String[] values = new String[] {"Park","Café","Nachtclub","Straat","School/Opleiding"};

        // Definieert nieuwe Adapter
        // Eerste paramater = context
        // Tweede parameter = layout voor rijen
        // Derde parameter = ID voor de textView
        // Vierde = data array

        ArrayAdapter <String> adapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1,android.R.id.text1, values);

        //Adapter instellen aan lijst
        listView.setAdapter(adapter);

        //onClick event voor lijst
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                //listview clicked item index
                int itemPosition = position;

                //listview clicked item value
                String itemValue = (String) listView.getItemAtPosition(position);

                //show alert
                Toast.makeText(getApplicationContext(),
                        "Position: "+itemPosition+" Listitem: " +itemValue, Toast.LENGTH_LONG).show();


            }
        });


    }


    @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_list, 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_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_list, container, false);
            return rootView;
        }
    }
}

This is my XML file

<LinearLayout 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:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context="com.example.aland.intrigueme.listActivity$PlaceholderFragment">

    <ListView android:layout_width="match_parent"
        android:layout_height="fill_parent"
        android:id="@+id/list" />


</LinearLayout>

and this is the error I get

01-17 19:02:43.080    2830-2830/com.example.aland.intrigueme E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.aland.intrigueme, PID: 2830
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.aland.intrigueme/com.example.aland.intrigueme.listActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            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)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
            at com.example.aland.intrigueme.listActivity.onCreate(listActivity.java:49)
            at android.app.Activity.performCreate(Activity.java:5933)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            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)
01-17 19:03:50.460    2830-2830/com.example.aland.intrigueme I/Process﹕ Sending signal. PID: 2830 SIG: 9
01-17 19:04:16.630    2870-2870/com.example.aland.intrigueme D/AndroidRuntime﹕ Shutting down VM
01-17 19:04:16.630    2870-2870/com.example.aland.intrigueme E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.aland.intrigueme, PID: 2870
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.aland.intrigueme/com.example.aland.intrigueme.listActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            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)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
            at com.example.aland.intrigueme.listActivity.onCreate(listActivity.java:49)
            at android.app.Activity.performCreate(Activity.java:5933)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            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)
01-17 19:04:19.400    2870-2870/com.example.aland.intrigueme I/Process﹕ Sending signal. PID: 2870 SIG: 9

Likely the listview is in the fragment and not activity layout. http://stackoverflow.com/questions/23653778/nullpointerexception-accessing-views-in-oncreate — laalto, Jan 17 '15 at 19:27
It is certainly a duplicate of the general problem. The `ListView` does not exist yet, as `commit()` is asynchronous, and so the fragment has not yet been called with `onCreateView()`. Move everything from your activity's `onCreate()` into `onViewCreated()` of your fragment. — CommonsWare, Jan 17 '15 at 20:17
FYI: Unless you describe concisely and convincingly how and why that's not a duplicate, you stating it won't have any (positive) effect at all. — Deduplicator, Jan 17 '15 at 22:40

score 1 · Answer 1 · answered Jan 17 '15 at 19:28

Well, a null pointer indicates that you're trying to access an object (probably) that hasn't been initialized. I'm having the same problem, my recommendation is to use the Log.i(String a, String b) method on essentially every line of your code and see when your objects are being initialized and when they're being queried.

String a is the "tag" in your log file, keep it the same to find your breadcrumbs more easily. String b should be used for your own description of what's going on at that specific line of code.

Good luck.

Getting a nullpointerexception here for things I don't understand

1 Answers1