FlexCel Studio for .NET

This skill helps write C# / VB.NET / F# code that uses FlexCel — the TMS Software library for working with Excel .xlsx / .xls files, exporting to PDF / HTML / SVG / images, and generating data-driven reports from templates. Works with .NET Framework 4.6+, .NET Core / .NET 5+, .NET Standard 2.0+, .NET MAUI, Xamarin, and .NET 9 Native AOT (with caveats — see below).

When to use this skill

Activate whenever the user wants to, from .NET code:

• Read an Excel file (.xlsx or .xls) — cell values, formulas, formatting.
• Create or modify an Excel file programmatically.
• Generate reports by merging data into Excel templates.
• Export an Excel file to PDF, HTML, SVG, or images.
• Autofit rows/columns, render sheets, or measure cells.
• Target .NET Framework, .NET Core / .NET 5+, .NET MAUI, Xamarin, Blazor server, ASP.NET Core, or Native AOT.

FlexCel does not require Excel or any Office installation on the target machine. No OLE/COM, no interop. Fully managed — works on Windows, Linux, macOS, iOS, and Android.

Two ways to create Excel files — pick one

Before writing code, decide which API fits the task:

When the user says "generate a report with company logo / nice formatting / many rows from a database", prefer Reports. When they say "read this file and extract values" or "create an Excel file with these calculations", prefer the API.

You can combine both: run a report to produce an in-memory XlsFile, then manipulate it with the API, then export to PDF.

Package and namespace reference

NuGet package: TMS.FlexCel (includes almost all functionality). Install via dotnet add package TMS.FlexCel after configuring the TMS NuGet source — FlexCel is hosted at TMS's own NuGet feed, not on nuget.org. See guides/installation-guide.md in the doc source for feed setup.

Optional companion packages:

• TMS.FlexCel.WinForms — WinForms preview / grid components.
• TMS.FlexCel.WebForms — legacy WebForms viewer (rarely needed).

Namespaces — add per task:

Note: Unlike the VCL edition, .NET has no platform-support unit/assembly to register in the entry point — all platform integration ships with the core package. Just reference TMS.FlexCel and you're done.

Critical gotchas (read this every time)

1. 1-based indexing for rows, columns, and sheets. xls.SetCellValue(1, 1, ...) writes to A1. XF (format) indices are the single exception — they are 0-based.
2. No T prefix on class names. VCL has TXlsFile, TFlexCelReport, TFlexCelPdfExport. .NET has XlsFile, FlexCelReport, FlexCelPdfExport. However value-type structs keep the T — TFormula, TFlxFormat, TCellAddress, TRichString, TExcelFileFormat, TFlxFormulaErrorValue.
3. GetCellValue returns object. There is no TCellValue discriminated union in .NET. Dispatch with is pattern matching:

   if (cell == null)                       { /* empty */ }
   else if (cell is string s)              { /* plain text */ }
   else if (cell is TRichString rs)        { /* rich text */ }
   else if (cell is double d)              { /* number (dates too!) */ }
   else if (cell is bool b)                { /* boolean */ }
   else if (cell is TFlxFormulaErrorValue) { /* #DIV/0 etc. */ }
   else if (cell is TFormula f)            { /* formula */ }
   

4. Never iterate with ColCount — it scans the whole sheet. Use ColCountInRow(row) + GetCellValueIndexed(row, colIdx, ref XF) + ColFromIndex(row, colIdx) — this is sparse-aware and dramatically faster on real files.
5. Dates are double. Excel stores dates as numbers with a date format. Cell returns double. Check the cell's XF number-format to know it's a date (or use TFlxNumberFormat.FormatValue helpers).
6. Memory. XlsFile, FlexCelReport, and the export classes hold the full workbook in memory. They are fully managed — GC handles cleanup. However, the export classes (FlexCelPdfExport, FlexCelHtmlExport, FlexCelImgExport) and FlexCelReport implement IDisposable; wrap them in using. XlsFile does not require using, but don't hold big workbooks as long-lived statics.
7. Use APIMate. For anything Excel-specific ("how do I add a data validation / a conditional format / a chart / a pivot table?"), the canonical answer is: build it in Excel → open the file in APIMate (ships with FlexCel, also available for Linux and macOS) → copy the generated C# or VB.NET code. Tell the user this.
8. Native AOT (.NET 9+): XlsFile and the exporters are fully supported. FlexCelReport uses reflection on your POCO types — annotate them with [DynamicallyAccessedMembers(...)] or reports fail silently after trimming. See references/pitfalls.md.

Quick-start recipes

All examples are C#. For VB.NET, translate syntactically — APIs are identical.

Recipe 1 — Create an Excel file

using System;
using System.IO;
using FlexCel.Core;
using FlexCel.XlsAdapter;

class Program
{
    static void Main()
    {
        // Empty workbook: 1 sheet, Excel-2019 default formatting.
        var xls = new XlsFile(1, TExcelFileFormat.v2019, true);

        xls.SetCellValue(1, 1, "Hello from FlexCel!");       // A1 text
        xls.SetCellValue(2, 1, 7);                           // A2 number (stored as double)
        xls.SetCellValue(3, 1, 11.3);                        // A3 number
        xls.SetCellValue(4, 1, new TFormula("=Sum(A2:A3)")); // A4 formula

        xls.Save(Path.Combine(
            Environment.GetFolderPath(Environment.SpecialFolder.Personal),
            "test.xlsx"));
    }
}

Key points:

• Indices are 1-based: (1, 1) = A1.
• File format is inferred from the extension (.xlsx → OOXML, .xls → BIFF8). Override via xls.Save(stream, TFileFormats.Xlsx) when saving to streams.
• SetCellValue(1, 1, "7") writes a string "7"; SetCellValue(1, 1, 7) writes a number 7. Type dispatch happens through method overloads.

Recipe 2 — Read an Excel file

using System;
using System.IO;
using FlexCel.Core;
using FlexCel.XlsAdapter;

void ReadExcel(string path)
{
    var xls = new XlsFile(path);
    xls.ActiveSheetByName = "Sheet1";   // or: xls.ActiveSheet = 1..xls.SheetCount

    for (int row = 1; row <= xls.RowCount; row++)
    {
        // Use ColCountInRow, NOT ColCount — much faster. See performance guide.
        for (int colIndex = 1; colIndex <= xls.ColCountInRow(row); colIndex++)
        {
            int XF = -1;
            object cell = xls.GetCellValueIndexed(row, colIndex, ref XF);
            var addr = new TCellAddress(row, xls.ColFromIndex(row, colIndex));

            string kind =
                cell == null                    ? "empty"
              : cell is TRichString             ? "rich string"
              : cell is string                  ? "string"
              : cell is double                  ? "number"
              : cell is bool                    ? "bool"
              : cell is