How do I transfer gridview rows to data table and stop the data table contents from being overided by mutator method.

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.NET4.5

C#7.0

I am trying to get the string text out of a data grid view and store it in a data table so i can save the data table to a csv file. I have got 2 unbound columns that I have been able to read data to in the csv file. One is Description. The other is Data. Problem is when I debug I notice the datatable stays null no matter what I do. I've tried everything.

Does anyone know how I can fix it? I have a mutator method called ProcessSettingFileCMD and I realize I am overiding the data table with it so it will never get actual grid view rows or null data. You want to see

mmuSaveAs_Click

and

My Settings form containing the data grid view.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

public partial class frmSettings : Form

    {
        #region Declarations

        protected string FileName;
        protected bool Modified;
        Setting _objSetting = new Setting();
        OpenFileDialog openFD = new OpenFileDialog();
        SaveFileDialog saveFD = new SaveFileDialog();
        DataTable _dt = new DataTable(); 

        #endregion

        #region Initializers
        public frmSettings()
        {            
            InitializeComponent();
            lblMessage.Text = "Please create or open a setting file.";
            gvSettings.DataSource = _dt;
            //Populate_grid_View_with_dummy_data();
        }

        private void Populate_grid_View_with_dummy_data()
        {
            string[] row0 = {"Address", "76 Douglas St Wakecorn"};
            string[] row1 = {"Property name", "Wakecorn University"};
            string[] row2 = {"Building", "C Block"};
            string[] row3 = { "Room", "C2.18"};

            gvSettings.Rows.Add(row0);
            gvSettings.Rows.Add(row1);
            gvSettings.Rows.Add(row2);
            gvSettings.Rows.Add(row3);
        }

        #endregion

        #region Buttons

        private void mnuQuit_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            if (SaveIfModified())
                Close();
        }
        #endregion Buttons

        #region File menu strip actions
        private void mmuSaveAs_Click(object sender, EventArgs e)
        {
            Cursor = Cursors.WaitCursor;
            saveFD.FileName = FileName;

            try
            {                
                saveFD.Title = "Save a CSV File as desired.";
                saveFD.Filter = "CSV|*.csv";
                saveFD.FileName = "default";
                txtFilePath.Text = openFD.FileName;

                if (saveFD.ShowDialog(this) == DialogResult.OK)
                    _dt = _objSetting.ProcessSettingFileCMD(saveFD.FileName);
            }
            catch (Exception ex)
            {
                Debug.WriteLine(String.Format("Error writing to {0}.\r\n\r\n{1}", FileName, ex.Message));
            }

            finally
            {
                Cursor = Cursors.Default;
            }
        }

My Settings class where the data table is passed back and forth through to the CRUD methods.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Data;
using CsvFile;
using System.Diagnostics;

public class Setting
    {
        #region Variables

        private int[] _intArrRow;
        private int _intCsvRow = 4;
        private DataTable _dt;
        DataColumn _dclColumnDescription = new DataColumn("Description", typeof(string));
        DataColumn _dclColumnData = new DataColumn("Data", typeof(string));
        #endregion

        #region Mutator Methods

        public DataTable ProcessSettingFileCMD(string filePath)
        {     
            //READ
            if (_dt == null)
            {
                 populateControlWithCSVData(filePath);
            }            

            //WRITE
            else if (_dt != null)
            {
                if (_dt.Rows.Count > 0)
                {
                    WriteFile(filePath);
                }
            }
            return _dt;
        }
        #endregion
		
        #region CRUD Methods

        private int GetTotalColumnsInTable()
        {
            int maxColumn = 0;
            foreach (DataRow row in _dt.Rows)
            {
                if (_dt.Columns.Contains("{0}") || _dt.Columns.Contains("{1}")) 
                {
                    for(int col = row.ItemArray.Length -1; col >= 0; col--)
                    {
                        if(row.ItemArray.GetValue(col) != null)
                        {
                            if (maxColumn < (col + 1))
                                maxColumn = (col + 1);
                            continue;
                        }
                    }
                }                
            }
            return maxColumn;
        }

        private void WriteFile(string filename)
        { 
                int numColumns = GetTotalColumnsInTable();
                using (var writer = new CsvFileWriter(filename))//I'm using this guy's class. http://www.blackbeltcoder.com/Articles/files/reading-and-writing-csv-files-in-c
                {
                    foreach (DataRow row in _dt.Rows)
                    {
                        if (row != _dt.Rows[0])
                        {
                            List<string> columns = new List<string>();
                            for (int col = 0; col < numColumns; col++)
                                columns.Add((string)row.ItemArray.GetValue(col) ?? String.Empty);
                            writer.WriteRow(columns);
                        }
                    }
                }                    
        }   
		
		private void populateControlWithCSVData(string filePath)
        {
            _dt = new DataTable();
            List<string> columns = new List<string>();

            using (var reader = new CsvFileReader(filePath))//I'm using this guy's class. http://www.blackbeltcoder.com/Articles/files/reading-and-writing-csv-files-in-c
            {
                _dt.Columns.Add(_dclColumnDescription);
                _dt.Columns.Add(_dclColumnData);
                while (reader.ReadRow(columns))
                {
                    _dt.Rows.Add(columns.ToArray());
                }
            }
        }
        #endregion
	}

What I have tried:

I'm using this guy's library and project http://www.blackbeltcoder.com/Articles/files/reading-and-writing-csv-files-in-c#. I'm trying to abstract it and integrate it into mine because I need the data table globally accessible for the application. It was easy with reading data from csv as I am only really refactoring the code but now that I am trying to write to a csv, it's getting messy.