C#

private void MyOtherButton_Click(object sender, EventArgs e)
    {
    DataTable dataTable = new DataTable();

    foreach (DataGridViewColumn col in myDataGridView.Columns)
        {
        dataTable.Columns.Add(col.Name);
        }

    foreach (DataGridViewRow row in myDataGridView.Rows)
        {
        DataRow drow = dataTable.NewRow();
        foreach (DataGridViewCell cell in row.Cells)
            {
            drow[cell.OwningColumn.Name] = cell.Value;
            }
        // The drow (DataRow) has all the Data in its ItemArray property but it does not get saved into the datatable row.
        dataTable.Rows.Add(drow);
        dataTable.AcceptChanges();
        //The columns load but the data rows do not add or import

        }
    MyOtherDataGridView.DataSource = dataTable;
    }

if (myDGV.DataSource is BindingSource bs)
   {
   if (bs.DataSource is DataTable dt)
      {
      ... use the Datatable in dt here ...
      }
   }

private void saveToolStripMenuItem_Click(object sender, EventArgs e)
   {
       //      var dia = new System.Windows.Forms.SaveFileDialog();
       saveFileDialog1.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
       saveFileDialog1.Filter = "Excel Worksheets (*.xlsx)|*.xlsx|xls file (*.xls)|*.xls|All files (*.*)|*.*";
       saveFileDialog1.FileName = "";



       if (dataGridView1.DataSource is BindingSource SBind)   //bs)
       {
           if (SBind.DataSource is DataTable dataTable)
           {
               using (ExcelPackage package = new ExcelPackage())
               {
                   if (saveFileDialog1.ShowDialog() != DialogResult.Cancel)
                   {
                       try
                       {
                           ExcelWorksheet ws = package.Workbook.Worksheets.Add("Countries");
                           ws.Cells["A1"].LoadFromDataTable(dataTable, true);
                           package.SaveAs(new FileInfo(saveFileDialog1.FileName));
                       }
                       catch (Exception)
                       {
                           DialogResult reminder = MessageBox.Show("Cannot save file, file opened in another program.\nClose it first! ", "Save Failed", MessageBoxButtons.OK);
                       }
                   }
               }
           }
       }

   }

if (sender is TextBox tb)
   {
   ...

TextBox tb = null;
if (sender is TextBox)
   {
   tb = (TextBox) sender;
   ...

TextBox tb = sender as TextBox;
if (tb != null)
   {
   ...

// Export DataGridView Selected Row Contents to File

TextWriter writer = new StreamWriter(FilePathName);
            
if (dataGridView1.SelectedRows.Count != 0)
{
    try
    {
        foreach (DataGridViewRow row in dataGridView1.SelectedRows.Cast<DataGridViewRow>().Reverse())
        {
                {
                for (int j = 0; j < dataGridView1.Columns.Count; j++)
                {
                    if (j == dataGridView1.Columns.Count - 1)
                    {
                        writer.Write("\t" + row.Cells[j].Value.ToString());
                    }
                    else
                        writer.Write("\t" + row.Cells[j].Value.ToString() + "\t" + "|");
                }

                writer.WriteLine("");
            }
        }
        writer.Close();
    }
    catch
    { }
}