Skills

flexcel-net

Installation
SKILL.md

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:

If the user wants to… Use Why
Read existing files, or build files cell-by-cell in code XlsFile API (FlexCel.XlsAdapter) Full programmatic control; no designer required; Native-AOT-safe.
Produce the same report repeatedly from changing data, with a styled layout FlexCelReport + Excel template (FlexCel.Report) Non-programmers can edit the template in Excel; code only provides data.

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:

Task using
Any FlexCel code using FlexCel.Core;
Read / write xls/xlsx using FlexCel.XlsAdapter;
PDF / HTML / image export, autofitting using FlexCel.Render;
Low-level PDF access (sign, PDF/A, standalone PDF) using FlexCel.Pdf;
Template-based reports using FlexCel.Report;
WinForms components using FlexCel.Winforms;
ASP.NET helpers using FlexCel.AspNet;

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 TFlxFormulaErrorValue   ? "error"
              : cell is TFormula                ? "formula"
              :                                   "unknown";

            Console.WriteLine($"Cell {addr.CellRef} {kind}: {cell}");
        }
    }
}

Key points:

  • Iterate with ColCountInRow + GetCellValueIndexed + ColFromIndex. The three together skip empty cells and give you the real column number of each non-empty cell.
  • GetCellValueIndexed takes XF by ref and writes the cell's format index into it.
  • cell == null means the cell is empty (never allocated). A cell containing an empty string is a different thing.

Recipe 3 — Export Excel to PDF

using FlexCel.Core;
using FlexCel.XlsAdapter;
using FlexCel.Render;

void XlsxToPdf(string src, string dst)
{
    var xls = new XlsFile(src);
    using var pdf = new FlexCelPdfExport(xls, true);  // true = allow overwrite
    pdf.Export(dst);                                  // all visible sheets, honoring Excel page setup
}

For PDF/A, font subsetting, digital signatures, multi-workbook PDFs, or tuning fonts on Linux/Docker see references/pdf-html-export.md.

Recipe 4 — Run a report from a template

Assume an Excel template invoice-template.xlsx already exists, with tags like <#Customers.Name> inside a named range __Customers__ spanning the repeating row(s).

using System;
using System.Data;
using FlexCel.Core;
using FlexCel.XlsAdapter;
using FlexCel.Report;

void RunReport(DataTable customers)
{
    using var report = new FlexCelReport(true);   // true = allow overwrite

    // Supply data sources
    report.AddTable("Customers", customers);      // DataTable / DataSet / IEnumerable<T>

    // Scalar values
    report.SetValue("ReportDate", DateTime.Now);
    report.SetValue("CompanyName", "Acme Corp");

    report.Run("invoice-template.xlsx", "invoice-output.xlsx");
}

AddTable overloads (the most common):

report.AddTable("Customers", customerList);          // IEnumerable<T> / List<T> / IQueryable<T>
report.AddTable("Customers", customerDataTable);     // DataTable
report.AddTable(customerDataSet);                    // DataSet — each contained DataTable by name
report.AddTable(myCustomerList);                     // single-arg: band name inferred from type name

To output directly to PDF — run the report into a fresh XlsFile, then pipe that through FlexCelPdfExport:

var outXls = new XlsFile();
report.Run("template.xlsx", outXls);
using var pdf = new FlexCelPdfExport(outXls, true);
pdf.Export("report.pdf");

For the full tag language and template-design conventions see references/reports-cheatsheet.md.

When to consult the references

Load a reference file only when the task actually needs it — keeps context lean for simple tasks.

  • references/api-cheatsheet.md — deeper XlsFile / ExcelFile usage: formatting, fonts, colors, merging, row/column sizing, comments, images, charts, data validation, protection, named ranges, InsertAndCopyRange / DeleteRange / MoveRange, sheet management, streams, recalc, virtual mode.
  • references/reports-cheatsheet.md — full tag reference, named-range conventions for bands, master-detail, config sheets, user functions, events.
  • references/pdf-html-export.md — FlexCelPdfExport, FlexCelHtmlExport, FlexCelImgExport options: PDF/A, font embedding, digital signing, HTML5, image embedding, multi-workbook PDFs.
  • references/pitfalls.md — extended gotchas, Native AOT specifics, Docker/Linux fonts, locale, barcodes, conditional formats, strict xlsx.

When you need authoritative detail

The cheatsheets cover the common path. For anything deeper, fetch from the public documentation source:

  • Markdown source (raw): https://raw.githubusercontent.com/tmssoftware/TMS-FlexCel.NET-doc-src/main/<path>.md
    • Guides: guides/api-developer-guide.md, guides/reports-developer-guide.md, guides/reports-tag-reference.md, guides/pdf-exporting-guide.md, guides/html-exporting-guide.md, guides/performance-guide.md, guides/multiplatform-guide.md
    • Tips: tips/<topic>.md (one file per tip — includes native-aot.md)
    • API reference: api/FlexCel.XlsAdapter/XlsFile/<MemberName>.md, api/FlexCel.Report/FlexCelReport/<MemberName>.md, etc.
  • Rendered docs: https://doc.tmssoftware.com/flexcel/net/index.html
  • Official sample repository (C# + VB.NET, desktop + mobile): https://github.com/tmssoftware/TMS-FlexCel.NET-demos

Use WebFetch on the raw markdown URL when you need to confirm a signature or pull an official example. Prefer the raw markdown over the rendered HTML.

Style expectations for generated code

  • Use using declarations / blocks for FlexCelReport, FlexCelPdfExport, FlexCelHtmlExport, FlexCelImgExport. They're IDisposable.
  • XlsFile does not implement IDisposable; don't wrap it in using. Let it go out of scope and GC will collect it.
  • Use 1-based literals explicitly (SetCellValue(1, 1, ...)) — never pretend indices are 0-based.
  • Use is pattern matching (or switch expressions on type) for GetCellValue results — don't cast blindly.
  • When providing PDF font folders, fall back gracefully: on Linux/macOS/Docker the fonts used by the workbook may not exist on the target. Use FlexCelPdfExport.GetFontFolder or GetFontData events.
  • For Native AOT: always annotate POCOs passed to FlexCelReport.AddTable with [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.PublicMethods)]. Without it, trimming will silently strip property accessors.
  • Don't invent method names. If unsure, check the API markdown under api/<namespace>/<class>/<member>.md in the doc source, or tell the user to verify with APIMate.
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Apr 19, 2026