Question

I would like my screen to have a listview with a header.

In my XML file, I have a listview and just above it there is an imageview, which is being used as the header.

When I run this I get an error. I have gone through dozens of tutorials and I can’t see what I am doing wrong. I have searched Stackoverflow and all tried the solutions but had no joy. Can anybody help me please?

Note: I am using Actionbarsherlock, so my class extends SherlockListActivity. I have tried this with ListActivity and get the same problem. I have also tried running without instantiating the image to see if the listview loads itself, and still I get the same error.

Please see my XML and code below:

My XML

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<ImageView
    android:id="@+id/headerimage"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:src="@drawable/header" >
</ImageView>

<ListView
    android:id="@+id/mylist"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >
</ListView>

My code:

public class MainActivity extends SherlockListActivity {

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    ImageView header = (ImageView) findViewById(R.id.headerimage);
    ListView listView = (ListView) findViewById(R.id.mylist);
    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
    "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
    "Linux", "OS/2" };

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

        listView.addHeaderView(header);
    listView.setAdapter(adapter);




}

Error log

E/AndroidRuntime(10642): FATAL EXCEPTION: main
E/AndroidRuntime(10642): java.lang.RuntimeException: Unable to start activity ComponentInfo{ttj.android.t3w/ttj.android.t3w.MainActivity}: java.lang.NullPointerException
E/AndroidRuntime(10642):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1968)
E/AndroidRuntime(10642):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1993)
E/AndroidRuntime(10642):    at android.app.ActivityThread.access$600(ActivityThread.java:127)
E/AndroidRuntime(10642):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1159)
E/AndroidRuntime(10642):    at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(10642):    at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(10642):    at android.app.ActivityThread.main(ActivityThread.java:4507)
E/AndroidRuntime(10642):    at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(10642):    at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime(10642):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
E/AndroidRuntime(10642):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
E/AndroidRuntime(10642):    at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(10642): Caused by: java.lang.NullPointerException
E/AndroidRuntime(10642):    at ttj.android.t3w.MainActivity.onCreate(MainActivity.java:40)
E/AndroidRuntime(10642):    at android.app.Activity.performCreate(Activity.java:4465)
E/AndroidRuntime(10642):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1052)
E/AndroidRuntime(10642):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1932)
E/AndroidRuntime(10642):    ... 11 more

Answer 1

FIXED.

The activity should NOT extend ListActivity. I changed it to Activity and the problem has gone.