android listview doesn't update

I am having a problem with using date range with a listView populated from a sqlite database, The code works perfectly however the issue i'm having is that the listView doesn't be updated (refreshed) when i choose another date range (when i touch the 'search' button again) , although the data adapter indeed gets the data from the database (made sure of that by using logcat)but doesn't print it in the listView. I can't use function notifyDataSetChanged(), it is not working, and whenever i use it after add() the app crashes.

Here is the code :-

public class ProductionCommentsActivity extends Activity implements View.OnClickListener {
private DBHandler dbHandler;
private ListView listView;
private Context context;
private ArrayList<String> results = new ArrayList<String>();
private ArrayAdapter adapter;
private static String newline = System.getProperty("line.separator");//a variable for line break
private EditText editTextFrom, editTextTo;
private DatePickerDialog datePickerDialogFrom, datePickerDialogTo;
private SimpleDateFormat simpleDateFormat;
private String fromDate,toDate ; // variables to store the chosen dates

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_production_comments);

    dbHandler = new DBHandler(this, dbHandler.DATABASE_NAME_PRODUCTION, null, 1);
    try {
        dbHandler.copyDataBase();
        Log.d("copydb", dbHandler.getDatabaseName());
    } catch (IOException e) {
        e.printStackTrace();
        Log.d("copydb",e.getMessage());
    }

    //defining list view
    listView = (ListView) findViewById(R.id.listView);

    //defining edit texts properties
    editTextFrom = (EditText) findViewById(R.id.editTextFrom);
    editTextFrom.setInputType(InputType.TYPE_NULL);
    editTextFrom.requestFocus();

    editTextTo = (EditText) findViewById(R.id.editTextTo);
    editTextTo.setInputType(InputType.TYPE_NULL);

    //setting up the date format
    simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd", Locale.US);
    setDateTimeField();
    context = this;
}

//method to handle the date pickers properties
private void setDateTimeField() {
    editTextFrom.setOnClickListener((View.OnClickListener) ProductionCommentsActivity.this);
    editTextTo.setOnClickListener((View.OnClickListener) ProductionCommentsActivity.this);

    //creating a new instance of the calendar
    Calendar newCalendar = Calendar.getInstance();

    //creating a pop up date picker
    datePickerDialogFrom = new DatePickerDialog(this, new DatePickerDialog.OnDateSetListener() {

        //getting the chosen date and setting its format
        //and writing the chosen date in the edit text
        public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
            Calendar newDate = Calendar.getInstance();
            newDate.set(year, monthOfYear, dayOfMonth);
            editTextFrom.setText(simpleDateFormat.format(newDate.getTime()));
            fromDate = editTextFrom.getText().toString();
        }

    },newCalendar.get(Calendar.YEAR), newCalendar.get(Calendar.MONTH),
            newCalendar.get(Calendar.DAY_OF_MONTH));

    datePickerDialogTo = new DatePickerDialog(this, new DatePickerDialog.OnDateSetListener() {

        public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
            Calendar newDate = Calendar.getInstance();
            newDate.set(year, monthOfYear, dayOfMonth);
            editTextTo.setText(simpleDateFormat.format(newDate.getTime()));
            toDate = editTextTo.getText().toString();
        }

    },newCalendar.get(Calendar.YEAR), newCalendar.get(Calendar.MONTH),
            newCalendar.get(Calendar.DAY_OF_MONTH));
}

// on click method to handle which edit text was touched
// and show the appropriate pop up calendar
@Override
public void onClick(View view) {
    if(view == editTextFrom) {
        datePickerDialogFrom.show();
    } else if(view == editTextTo) {
        datePickerDialogTo.show();
    }
}

//method to set format of date and attach the array adapter to the list view
public void searchDates(View view){
    if(!editTextFrom.getText().toString().matches("From:")
            && !editTextTo.getText().toString().matches("To:")) {
            setDateTimeField();
            getProductionComments(fromDate, toDate);
            adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, results);
            listView.setAdapter(adapter);
        Log.d("fire",adapter.toString());
    }else{
        Toast.makeText(this,"Please enter valid dates", Toast.LENGTH_LONG).show();
    }
}

//get production comments data
public void getProductionComments(String from, String to) {
    try {
        SQLiteDatabase db = dbHandler.getReadableDatabase();

        String query = "SELECT Date,Item,Comments FROM ProductionCommentData WHERE Date " +
                "BETWEEN ? AND ? ORDER BY Date DESC";
        Cursor cursor = db.rawQuery(query,new String[]{from,to});

        if (cursor != null) {
            if (cursor.moveToFirst()) {
                do {
                    String date = cursor.getString(cursor.getColumnIndex("Date"));
                    String item = cursor.getString(cursor.getColumnIndex("Item"));
                    String comments = cursor.getString(cursor.getColumnIndex("Comments"));
                    results.add("Date: " + date.substring(0, 10) + newline + newline +
                            "Item: " + item + newline + newline + comments);
                } while (cursor.moveToNext());
            }else{
                Toast.makeText(this,"No Data was found for the chosen dates",Toast.LENGTH_LONG).show();
            }
        }
    } catch (SQLiteException se){
        Log.e(getClass().getSimpleName(), se.getMessage());
    }
}

Here is the layout code:-

<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
xmlns:tools="http://ift.tt/LrGmb4" 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="com.qarun.qpcbeta.ProductionCommentsActivity"
android:id="@+id/relativeLayout">


<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="Production Comments"
    android:id="@+id/textView6"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true" />

<EditText
    android:layout_width="100dp"
    android:layout_height="wrap_content"
    android:inputType="date"
    android:ems="10"
    android:id="@+id/editTextFrom"
    android:layout_below="@+id/textView6"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_marginTop="29dp"
    android:editable="false"
    android:textSize="13sp"
    android:text="From:"
    android:focusable="false"/>

<EditText
    android:layout_width="100dp"
    android:layout_height="wrap_content"
    android:inputType="date"
    android:ems="10"
    android:id="@+id/editTextTo"
    android:layout_alignTop="@+id/editTextFrom"
    android:layout_toLeftOf="@+id/btnSearch"
    android:layout_toStartOf="@+id/btnSearch"
    android:textSize="13sp"
    android:textIsSelectable="false"
    android:text="To:"
    android:focusable="false"/>

<ListView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/listView"
    android:layout_below="@+id/editTextTo"
    android:layout_alignParentRight="true"
    android:layout_alignParentEnd="true"/>

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Search"
    android:id="@+id/btnSearch"
    android:onClick="searchDates"
    android:layout_above="@+id/listView"
    android:layout_alignRight="@+id/listView"
    android:layout_alignEnd="@+id/listView"/>

thanks in advance