save to existing excel file without opening new excel file

Question

I have sample code block and you can see below and this code working effectively. But this code not enough for me. So i need improve my code. Firstly, i have datagridview and this datagridview creating my datablock but i could not write new row to under before row. When i add new data block to datagridvew then new data has must write under older data on excel file.

private void buttonExcel_Click(object sender, EventArgs e)
        {
            // creating Excel Application  
            Microsoft.Office.Interop.Excel._Application app = new Microsoft.Office.Interop.Excel.Application();
            // creating new WorkBook within Excel application  
            Microsoft.Office.Interop.Excel._Workbook workbook = app.Workbooks.Add(Type.Missing);
            // creating new Excelsheet in workbook  
            Microsoft.Office.Interop.Excel._Worksheet worksheet = null;
            // see the excel sheet behind the program  
            app.Visible = true;
            // get the reference of first sheet. By default its name is Sheet1.  
            // store its reference to worksheet  
            worksheet = workbook.Sheets["Sheet1"];
            worksheet = workbook.ActiveSheet;
            // changing the name of active sheet  
            worksheet.Name = "Exported from gridview";
            // storing header part in Excel  
            for (int i = 1; i < dataGridView1.Columns.Count + 1; i++)
            {
                worksheet.Cells[1, i] = dataGridView1.Columns[i - 1].HeaderText;
            }
            // storing Each row and column value to excel sheet  
            for (int i = 0; i < dataGridView1.Rows.Count - 1; i++)
            {
                for (int j = 0; j < dataGridView1.Columns.Count; j++)
                {
                    worksheet.Cells[i + 2, j + 1] = dataGridView1.Rows[i].Cells[j].Value.ToString();
                }
            }
            // save the application  

            workbook.SaveAs("c:\\PROJE TEKLİF FİYAT.xlsx", Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Microsoft.Office.Interop.Excel.XlSaveAsAccessMode.xlExclusive, Type.Missing, Type.Missing, Type.Missing, Type.Missing);
            // Exit from the application  
            app.Quit();
        }

Answer 1

I'd used the ClosedXML Library (via NuGet) for this as it makes saving a datatable to excel pretty simple.

First, import your existing spreadsheet as a datatable like so:

    public DataTable GetData(string filename)
    {
        using (XLWorkbook workBook = new XLWorkbook(filename))
        {
            //Read the first Sheet from Excel file.
            IXLWorksheet workSheet = workBook.Worksheet(1);

            //Create a new DataTable.
            DataTable dt = new DataTable();

            //Loop through the Worksheet rows.
            bool firstRow = true;
            foreach (IXLRow row in workSheet.Rows())
            {
                //Use the first row to add columns to DataTable.
                if (firstRow)
                {
                    foreach (IXLCell cell in row.Cells())
                    {
                        dt.Columns.Add(cell.Value.ToString());
                    }
                    firstRow = false;
                }
                else
                {
                    //Add rows to DataTable.
                    dt.Rows.Add();
                    int i = 0;

                    foreach (IXLCell cell in row.Cells(row.FirstCellUsed().Address.ColumnNumber, row.LastCellUsed().Address.ColumnNumber))
                    {
                        dt.Rows[dt.Rows.Count - 1][i] = cell.Value.ToString();
                        i++;
                    }
                }
            }
            return dt;
        }
    }

Then convert datagridview to datatable, then merge the existing data w/ the datagridview data into one datatable, then save as XLSX.

using ClosedXML.Excel;
...
private void saveDGV(DataTable existing)
{
    //Creating DataTable.
    DataTable dt = new DataTable();
 
    //Adding the Columns.
    foreach (DataGridViewColumn column in dataGridView1.Columns)
    {
        dt.Columns.Add(column.HeaderText, column.ValueType);
    }
 
    //Adding the Rows.
    foreach (DataGridViewRow row in dataGridView1.Rows)
    {
        dt.Rows.Add();
        foreach (DataGridViewCell cell in row.Cells)
        {
            dt.Rows[dt.Rows.Count - 1][cell.ColumnIndex] = cell.Value.ToString();
        }
    }
    existing.Merge(dt);
    using (XLWorkbook wb = new XLWorkbook())
    {
        wb.Worksheets.Add(existing, "Exported from gridview");
        //Adjust widths of Columns.
        wb.Worksheet(1).Columns().AdjustToContents();
        wb.SaveAs("c:\\PROJE TEKLİF FİYAT.xlsx")
    }
}

You would use this like so:

using ClosedXML.Excel;
...
private void buttonExcel_Click(object sender, EventArgs e)
        {
            DataTable existing = GetData("c:\\PROJE TEKLİF FİYAT.xlsx");
            saveDGV(existing);
        }