notifySetDataChanged() throws NullPointer Exception in custom adapter for list view

Question

I've made a custom array adapter which changes the strings of two textViews in my list layout. The problem is that when I call the notifySetDataChanged() function, it throws a null pointer exception. Even after referring to various online forums, I'm unable to determine the source of this error.

Here's my code:

MessageAdapetr.java

import java.util.ArrayList;
import java.util.List;
import android.annotation.SuppressLint;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

@SuppressLint("ViewHolder") public class MessageAdapter extends ArrayAdapter<TextMessage> {


 private Context context;
 public List<TextMessage> message;

    public MessageAdapter(Context context, List<TextMessage> message)
    {
        super(context, R.layout.message_layout);
        this.context = context;
        this.message = new ArrayList<TextMessage>();
        this.message = message;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) 
    {
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        View rowView = inflater.inflate(R.layout.message_layout, parent, false);

        TextView your_first_text_view = (TextView) rowView.findViewById(R.id.textView1);
        TextView your_second_text_view = (TextView) rowView.findViewById(R.id.textView2);

        your_first_text_view.setText(message.get(position).getContent());
        your_second_text_view.setText(message.get(position).getSender());

        return rowView;
    }
}

EditTextMessage.java

public class EditTextMessage extends ListActivity {

private TextMessage mTextMessage;
private EditText contentEditText;
private String content;
private Button sendButton;
private List<TextMessage> posts;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
    getActionBar().setDisplayHomeAsUpEnabled(true);
    setContentView(R.layout.activity_edit_text_message);

            posts = new ArrayList<TextMessage>();

        //
            ListView my_list_view = (ListView) findViewById(android.R.id.list);
            MessageAdapter my_adapter = new MessageAdapter(this, posts);
            my_list_view.setAdapter(my_adapter);
        //

    contentEditText = (EditText) findViewById(R.id.TypeMessage);

    sendButton = (Button)findViewById(R.id.SendButton);
    sendButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            saveNote();

        }
    });

    //Refreshes posts
            refreshPostList();
}

private void saveNote() {

    Intent intent = this.getIntent();

    content = contentEditText.getText().toString(); //contents of the edit text are stored in a string variable

    content = content.trim();


        if (!content.isEmpty()) {

            final ParseObject post = new ParseObject("Message");

            post.put("msg", content);
            post.put("sent", intent.getStringExtra("memberId"));
            post.put("sender", ParseUser.getCurrentUser());
            post.put("msg_sender", ParseUser.getCurrentUser().getString("username").toString());
            setProgressBarIndeterminateVisibility(true);
            post.saveInBackground(new SaveCallback() {
                public void done(ParseException e) {
                    setProgressBarIndeterminateVisibility(false);
                    if (e == null) {
                        // Saved successfully.
                        mTextMessage = new TextMessage(post.getObjectId(), content, post.getString("msg_sender"));
                        Toast.makeText(getApplicationContext(), "Sent", Toast.LENGTH_SHORT).show();
                        refreshPostList();

                    } else {
                        // The save failed.
                        Toast.makeText(getApplicationContext(), "Failed to send", Toast.LENGTH_SHORT).show();
                        Log.d(getClass().getSimpleName(), "User update error: " + e);
                    }
                }
            });
    } 
    else if (content.isEmpty()) {
        AlertDialog.Builder builder = new AlertDialog.Builder(EditTextMessage.this);
        builder.setMessage(R.string.edit_error_message)
            .setTitle(R.string.edit_error_title)
            .setPositiveButton(android.R.string.ok, null);
        AlertDialog dialog = builder.create();
        dialog.show();
    }
}

private void refreshPostList() {

    final Intent intent = this.getIntent();

    ParseQuery<ParseObject> query = ParseQuery.getQuery("Message");

    setProgressBarIndeterminateVisibility(true);

    query.findInBackground(new FindCallback<ParseObject>() {

        @Override
        public void done(List<ParseObject> postList, ParseException e) {
            setProgressBarIndeterminateVisibility(false);
            if (e == null) {
                // If there are results, update the list of posts
                // and notify the adapter
                posts.clear();
                for (ParseObject post : postList) {

                    if(
                            (post.getString("sent").toString().equals(ParseUser.getCurrentUser().getObjectId().toString())
                            &&(post.get("msg_sender").toString().equals(intent.getStringExtra("memberName"))))
                        ||
                            (post.get("msg_sender").toString().equals(ParseUser.getCurrentUser().getUsername().toString())
                            &&
                              (post.getString("sent").toString().equals(intent.getStringExtra("memberId"))))
                      )
                    {
                        TextMessage note = new TextMessage(post.getObjectId(), post.getString("msg"), 
                                post.getString("msg_sender"));
                        posts.add(note);

                    }
                }

               //
                ((MessageAdapter) getListAdapter())
                .notifyDataSetChanged();
               //

            } else {

                Log.d(getClass().getSimpleName(), "Error: Some error" + e.getMessage());

            }
        }
    });
}

}

Logcat:

09-25 00:54:01.900: E/AndroidRuntime(12896): FATAL EXCEPTION: main
09-25 00:54:01.900: E/AndroidRuntime(12896): java.lang.NullPointerException
09-25 00:54:01.900: E/AndroidRuntime(12896):    at ish.message.EditTextMessage$5.done(EditTextMessage.java:280)
09-25 00:54:01.900: E/AndroidRuntime(12896):    at com.parse.FindCallback.internalDone(FindCallback.java:45)
09-25 00:54:01.900: E/AndroidRuntime(12896):    at com.parse.FindCallback.internalDone(FindCallback.java:31)
09-25 00:54:01.900: E/AndroidRuntime(12896):    at com.parse.Parse$5$1.run(Parse.java:891)
09-25 00:54:01.900: E/AndroidRuntime(12896):    at android.os.Handler.handleCallback(Handler.java:615)
09-25 00:54:01.900: E/AndroidRuntime(12896):    at android.os.Handler.dispatchMessage(Handler.java:92)
09-25 00:54:01.900: E/AndroidRuntime(12896):    at android.os.Looper.loop(Looper.java:137)
09-25 00:54:01.900: E/AndroidRuntime(12896):    at android.app.ActivityThread.main(ActivityThread.java:4960)
09-25 00:54:01.900: E/AndroidRuntime(12896):    at java.lang.reflect.Method.invokeNative(Native Method)
09-25 00:54:01.900: E/AndroidRuntime(12896):    at java.lang.reflect.Method.invoke(Method.java:511)
09-25 00:54:01.900: E/AndroidRuntime(12896):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
09-25 00:54:01.900: E/AndroidRuntime(12896):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
09-25 00:54:01.900: E/AndroidRuntime(12896):    at dalvik.system.NativeStart.main(Native Method)

Feel free to ask for any more info. required. Thanks in advance.

Answer 1

change these lines:

public MessageAdapter(Context context, List<TextMessage> message)

super(context, R.layout.message_layout);

MessageAdapter my_adapter = new MessageAdapter(this, posts);

to

public MessageAdapter(Context context, int resource, List<TextMessage> message)

super(context, resource ,message);

MessageAdapter my_adapter = new MessageAdapter(this, R.layout.message_layout , posts);

you have not passed any objects to your adapter super constructor so when calling notifyDataSetChanged he changes nothing because he dose not have your list items to apply.

after that make sure you are changing the message object that you passed to your adapter, you must change one object reference not creating another and change that.

hope it helps you!