NPE in Custom list

Question

I am trying to make a custom list which is getting data from database and has two text views but its giving NPE and I am not getting why is it so and banged too much head.Please help Here is my code:

public class NotesList extends ListActivity{
    private DataSource datasource;
     ArrayAdapter<Message> adapter;
     CustomList adap;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.list);

       //  List<Message> values = datasource.getAllMessages();
     //  adapter = new ArrayAdapter<Message>(this, android.R.layout.simple_list_item_1, values);
    //  setListAdapter(adapter);
      adap = new CustomList();

      setListAdapter(adap);



    }
    @Override
    public void onResume() {
        datasource.open();

        super.onResume();
      }


      @Override
    public void onPause() {
        datasource.close();

        super.onPause();

      }
      public class CustomList extends BaseAdapter {

            List<Message> DataList = datasource.getAllMessages();
            @Override
            public int getCount() {
                // TODO Auto-generated method stub
                return DataList.size();
            }

            @Override
            public Message getItem(int arg0) {
                // TODO Auto-generated method stub
                return DataList.get(arg0);
            }

            @Override
            public long getItemId(int arg0) {
                // TODO Auto-generated method stub
                return arg0;
            }

            @Override
            public View getView(int arg0, View arg1, ViewGroup arg2) {

                if(arg1==null)
                {
                    LayoutInflater inflater = (LayoutInflater) NotesList.this.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                    arg1 = inflater.inflate(R.layout.listitem, arg2,false);
                }

                TextView heading = (TextView)arg1.findViewById(R.id.textView1);
                TextView notes = (TextView)arg1.findViewById(R.id.textView2);

                Message MessageObj = DataList.get(arg0);

                heading.setText(MessageObj.getmessage());
                notes.setText(MessageObj.getmessage());

                return arg1;
            }

            public Message getCodeLearnChapter(int position)
            {
                return DataList.get(position);
            }

        }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            // Inflate the menu; this adds items to the action bar if it is present.
         //   getMenuInflater().inflate(R.menu.list_view_with_simple_adapter, menu);
            return true;
        }

}

Logcat is:

03-19 07:24:00.936: E/AndroidRuntime(28816): FATAL EXCEPTION: main
03-19 07:24:00.936: E/AndroidRuntime(28816): java.lang.RuntimeException: Unable to start activity ComponentInfo{soft.b.notes/soft.b.notes.NotesList}: java.lang.NullPointerException
03-19 07:24:00.936: E/AndroidRuntime(28816):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
03-19 07:24:00.936: E/AndroidRuntime(28816):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
03-19 07:24:00.936: E/AndroidRuntime(28816):    at android.app.ActivityThread.access$600(ActivityThread.java:122)
03-19 07:24:00.936: E/AndroidRuntime(28816):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
03-19 07:24:00.936: E/AndroidRuntime(28816):    at android.os.Handler.dispatchMessage(Handler.java:99)
03-19 07:24:00.936: E/AndroidRuntime(28816):    at android.os.Looper.loop(Looper.java:137)
03-19 07:24:00.936: E/AndroidRuntime(28816):    at android.app.ActivityThread.main(ActivityThread.java:4340)
03-19 07:24:00.936: E/AndroidRuntime(28816):    at java.lang.reflect.Method.invokeNative(Native Method)
03-19 07:24:00.936: E/AndroidRuntime(28816):    at java.lang.reflect.Method.invoke(Method.java:511)
03-19 07:24:00.936: E/AndroidRuntime(28816):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-19 07:24:00.936: E/AndroidRuntime(28816):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)

Regards !

Answer 1

you never initialize datasource and invoking datasource.getAllMessages() cause the NPE

Answer 2

The NPE can be found below in your logcat, with helpful stacktrace to diagnose it.

One way to explain the NPE is that

List<Message> DataList = datasource.getAllMessages();

calls a method on datasource which is not initialized when you call new CustomList().