ListView android and null pointer exception

Question

I'm trying to show a simple ListView ,but I have some problems .It seems that I had a NullPointerException . Here's the XML :

 <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=".MainActivity">

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

and my main class :

 public class MainActivity extends Activity {

private List<String> exemple;
private ListView liste=(ListView) findViewById(R.id.listView);


protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

   exemple=new ArrayList<String>();

    exemple.add("Item 1");
    exemple.add("Item 2");
    exemple.add("Item 3");

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, exemple);
    liste.setAdapter(adapter);
}
}

I got this error :

07-07 11:59:27.024    2758-2758/tunisia_sat.com.essai E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: tunisia_sat.com.essai, PID: 2758
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{tunisia_sat.com.essai/tunisia_sat.com.essai.MainActivity}: java.lang.NullPointerException

move your private ListView liste=(ListView) findViewById(R.id.listView); in onCreate() after setContentView() — N J
– N J, Commented Jul 7, 2015 at 16:19

Green goblin · Accepted Answer · 2015-07-07 16:26:22Z

4

Move liste initialization after setContentView:

setContentView(R.layout.activity_main);
liste = (ListView) findViewById(R.id.listView);

Why NullPointerException?
You are calling ssetAdapter on null reference liste in the following line:

liste.setAdapter(adapter);

liste is null because it is being initialized before view is up(binding activity with view). So, findViewById returns Null.

edited Jul 7, 2015 at 16:26

answered Jul 7, 2015 at 16:19

Green goblin

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Comments

N J · Accepted Answer · 2015-07-07 16:20:55Z

2

Do not initialize ListView in declaration. Just do this:

public class MainActivity extends Activity {

private List<String> exemple;
private ListView liste;

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    liste = (ListView) findViewById(R.id.listView);

    exemple=new ArrayList<String>();
    exemple.add("Item 1");
    exemple.add("Item 2");
    exemple.add("Item 3");

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, exemple);
    liste.setAdapter(adapter);
}
}

edited Jul 7, 2015 at 16:20

N J

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answered Jul 7, 2015 at 16:20

diesersamat

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Comments

Max Pinto · Accepted Answer · 2015-07-07 16:26:39Z

0

You should Cast your listview after setting contentView int your onCreate method:

so you should do this:

outside your method, declare your ListView.

ListView listView;

So then cast in onCreate method:

listView=(ListView) findViewById(R.id.listView);

Regards.

answered Jul 7, 2015 at 16:26

Max Pinto

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2 Comments

N J Over a year ago

why to repeat answer ?

Max Pinto Over a year ago

well, maybe because when i write mi answer i didnt see the first one... perhaps was not intencionally.

Sanjeev · Accepted Answer · 2015-07-07 16:28:16Z

0

Write the following statement 

ListView liste=(ListView) findViewById(R.id.listView);

in Oncreate() method after 

setContentView(R.layout.activity_main);

Example:

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

ListView liste=(ListView) findViewById(R.id.listView); 

   exemple=new ArrayList<String>(); 
    exemple.add("Item 1");
    exemple.add("Item 2");
    exemple.add("Item 3");

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, exemple);
    liste.setAdapter(adapter);
}

answered Jul 7, 2015 at 16:28

Sanjeev

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1 Comment

N J Over a year ago

why to repeat answer ?

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