Android : CustomAdapter Overwrites Items in ListView - Android

This code works, but every time the button is clicked, it overwrites the items in List View instead of adding the items to the bottom of the list. Tried a lot but nothing has solved that issue.

 public static final class ChatRoom2 extends Activity {

    Button addButton;
    ListView listView;
    EditText editText;
    TextView values;
    ImageView userimage;
    ChatRow adapter;
    ChatRow adapter2;
    String message;



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

        Intent intent = getIntent();
        String sText = intent.getExtras().getString("textFromList");
        getActionBar().setTitle(sText);
        setContentView(R.layout.chatlayout2);


        this.getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_HIDDEN);

        final int[] images = {R.drawable.image01, R.drawable.image02, R.drawable.image03};


        final int imageId = (int)(Math.random() * images.length);
        userimage = (ImageView) findViewById(R.id.img);
        addButton = (Button) findViewById(R.id.button2);

        editText = (EditText) findViewById(R.id.editText);
        values = (TextView) findViewById(R.id.txt);

        final RowItems weather_data[] = new RowItems[]
                {
                        new RowItems(images[imageId],message)
                };

        adapter = new ChatRow(this,
                R.layout.chatmessage, weather_data);


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


        addButton.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {

                message = editText.getText().toString();
                RowItems messagedata[] = new RowItems[]{ new RowItems(images[imageId],message)
                };


                adapter2 = new ChatRow(ChatRoom2.this, R.layout.chatmessage, messagedata);
                listView.setAdapter(adapter2);


                adapter2.notifyDataSetChanged();

                editText.setText("");

                //minimize keyboard 
                InputMethodManager imm = (InputMethodManager)getSystemService(Context.
                        INPUT_METHOD_SERVICE);
                imm.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(), 0);

            }
        });
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> a, View v, int position,
                                    long id) {


                Toast.makeText(ChatRoom2.this, "clicked", Toast.LENGTH_LONG)
                        .show();




            }
        });

    }


}

Any Ideas?