I loop source files, open the file and the only worksheet, get the source range as worksheet use range, setup subsequent destination range, and add it to destination workbook and save it.

After some files can’t determine exactly the number when number of rows became high, I get exception

System.ArgumentOutOfRangeException:

at line

IRange destinationRange = destinationWorksheet.Range[currentDestFirstRow,currentDestFirstCol, currentDestLastRow, currentDestLastCol];

with the following value

destination range=[1037502,1,1047586,6]

If I stop loop after some files everything goes well, and destination file is generated correctly.

Beware that range parameters are int I don’t find any reason to be out of range.

Thanks for any suggestion

public Test()
{
    Syncfusion.Licensing.SyncfusionLicenseProvider.RegisterLicense("my_key");
    destinationFile = outputDataPath + "__merged.xlsx";

    // get list of file to merge
    filesToMerge = Directory.GetFiles(this.inputDatapath, "*.xlsx");

    using (ExcelEngine excelEngine = new ExcelEngine())
    {
        IApplication application = excelEngine.Excel;
        application.DefaultVersion = ExcelVersion.Excel2013;
        /* set destination  workbook and worksheet
         * initialize destination Range
         */ 
        IWorkbook destinationWorkbook = application.Workbooks.Create(1);
        IWorksheet destinationWorksheet = destinationWorkbook.Worksheets[0];

        int currentDestFirstRow = 1;
        int currentDestFirstCol = 1;
        int currentDestLastRow = 1;
        int currentDestLastCol;

        string currentFile;

        for (int i = 0; i < filesToMerge.Length - 1; i++)
        {
            /* get used range from worksheet of each input file
             * and copy to destination*/
            currentFile = filesToMerge[i];

            FileStream currentStream = new FileStream(currentFile, FileMode.Open, FileAccess.Read);
            IWorkbook currentWorkbook = application.Workbooks.Open(currentStream, ExcelOpenType.Automatic);
            IWorksheet currentWorksheet = currentWorkbook.Worksheets[0];
            IRange currentSourceRange = currentWorksheet.UsedRange;

            if (i == 0)
            {
                currentDestFirstRow = 1;
                currentDestFirstCol = 1;
                currentDestLastRow = currentSourceRange.LastRow;
                currentDestLastCol = currentSourceRange.LastColumn;
            }
            else
            {
                currentDestFirstRow = currentDestLastRow + 1;
                currentDestFirstCol = 1;
                currentDestLastRow = currentDestFirstRow + currentSourceRange.LastRow;
                currentDestLastCol = currentSourceRange.LastColumn;
            }

            IRange destinationRange = destinationWorksheet.Range[currentDestFirstRow, currentDestFirstCol, currentDestLastRow, currentDestLastCol];
            currentSourceRange.CopyTo(destinationRange);
            string line = (i.ToString()).PadLeft(3, '0')+Environment.NewLine;
            line += $"file={currentFile}" + Environment.NewLine;
            line += $"destination range=[{currentDestFirstRow},{currentDestFirstCol},{currentDestLastRow},{currentDestLastCol}]";
            Console.WriteLine(line);
        }

        FileStream stream = new FileStream(destinationFile, FileMode.OpenOrCreate, FileAccess.ReadWrite);
        destinationWorkbook.SaveAs(stream);
        destinationWorkbook.Close();
        stream.Close();
        excelEngine.Dispose();
    }
}