opening an existing empty spreadsheet and writing data into it - asp.net

Question

I have a spreadsheet with multiple pages in it.When I click on a button I need to open this spreadsheet and write all the data(dataset/datatable) returned from the database into one of the pages in the spreadsheet.I saw so many articles for exporting dataset to a new excel sheet.how do i open an existing spreadsheet and write a dataset into it using asp.net/C#?
Please help..
Thanks.
UPDATE:
Basically I have the following code to export a dataset to a new excel sheet.
private void createDataInExcel(DataSet ds)
{
Application oXL;
_Workbook oWB;
_Worksheet oSheet;
Range oRng;
string strCurrentDir = Server.MapPath(".") + "\\excelreports\\";
try
{
oXL = new Application();
oXL.Visible = false;
//Get a new workbook.
oWB = (_Workbook)(oXL.Workbooks.Add(Missing.Value));
oSheet = (_Worksheet)oWB.ActiveSheet;
//System.Data.DataTable dtGridData=ds.Tables[0];
int iRow = 2;
if (ds.Tables[0].Rows.Count > 0)
{
for (int j = 0; j < ds.Tables[0].Columns.Count; j++)
{
oSheet.Cells[1, j + 1] = ds.Tables[0].Columns[j].ColumnName;
}
// For each row, print the values of each column.
for (int rowNo = 0; rowNo < ds.Tables[0].Rows.Count; rowNo++)
{
for (int colNo = 0; colNo < ds.Tables[0].Columns.Count; colNo++)
{
oSheet.Cells[iRow, colNo + 1] = ds.Tables[0].Rows[rowNo][colNo].ToString();
}
iRow++;
}
}
oRng = oSheet.get_Range("A1", "IV1");
oRng.EntireColumn.AutoFit();
oXL.Visible = false;
oXL.UserControl = false;
string strFile = "excelreport" + DateTime.Now.Ticks.ToString() + ".xls";//+
oWB.SaveAs(strCurrentDir +strFile, XlFileFormat.xlWorkbookNormal, null, null, false, false, XlSaveAsAccessMode.xlShared, false, false, null,null, null);
// Need all following code to clean up and remove all references!!!
oWB.Close(null, null, null);
oXL.Workbooks.Close();
oXL.Quit();
Marshal.ReleaseComObject(oRng);
Marshal.ReleaseComObject(oXL);
Marshal.ReleaseComObject(oSheet);
Marshal.ReleaseComObject(oWB);
}
catch (Exception theException)
{
Response.Write(theException.Message);
}
Response.Write("data exported");
}
Is it possible to improve the above code to write the dataset to an existing sheet?Also with the above code its taking about a minute to write the data into excel sheet..I do not understand why is it taking that long.

Answer 1

not 100% sure where you are with your code, however using the excel com object referenced in your project you can open a workbook using the Workbooks._Open method, then you can get the sheet by name using the sheets collection of the workbook and the get_Item.
if you need to add a sheet to the workbook you can use the add on the sheets collect.
Maybe if you post the code you have we can suggest where to improve it.
this line
oWB = (_Workbook)(oXL.Workbooks.Add(Missing.Value));
is creating a new workbook. use
string workbookPath = "c:/SomeWorkBook.xls";
oWB = Workbooks.Open(workbookPath,
0, false, 5, "", "", false, Excel.XlPlatform.xlWindows, "",
true, false, 0, true, false, false);
now it depends on what you want to do add a new sheet, use an existing sheet etc.
this is a codeproject link that shows more in depth here