# Acad Fields

> Dynamic text fields — field codes, evaluation, embedding in MText/attributes

- Skill: `hebackus/acad-fields` (Agent Skill)
- Install (CLI): `npx skillmds@latest add hebackus/acad-fields`
- Raw SKILL.md: https://api.skillmd.com/api/skills/hebackus/acad-fields/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: hebackus (https://skillmd.com/u/hebackus)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/hebackus/acad-fields

---


# AutoCAD Fields (Dynamic Text)

Use this skill when creating or managing field objects - dynamic text that updates based on object properties, system variables, dates, formulas, or other data sources.

## Field Class

**Namespace:** `Autodesk.AutoCAD.DatabaseServices`
**Base class:** `DBObject`

### Creating a Field

```csharp
// Create a field that shows the current date
Field dateField = new Field("%<\\AcVar Date \\f \"M/d/yyyy\">%");

// Create a field that shows an object property
Field propField = new Field(
    string.Format("%<\\AcObjProp Object(%<\\_ObjId {0}>%).Area \\f \"%lu2%pr2\">%",
        entityId.Handle));

// Set evaluation options
dateField.EvaluationOption = FieldEvaluationOptions.OnOpen
    | FieldEvaluationOptions.OnSave
    | FieldEvaluationOptions.OnPlot;

// Evaluate the field
dateField.Evaluate();
```

## Common Field Code Patterns

```csharp
// Object property (area of a polyline)
string areaField = string.Format(
    "%<\\AcObjProp Object(%<\\_ObjId {0}>%).Area \\f \"%lu2%pr2\">%",
    entity.Handle);

// System variable
string dateField = "%<\\AcVar Date \\f \"M/d/yyyy\">%";
string fileNameField = "%<\\AcVar FileName>%";
string scaleField = "%<\\AcVar CANNOSCALE \\f \"%sc\">%";

// Formula field
string formulaField = "%<\\AcExpr (1 + 2) * 3>%";

// Sheet set fields
string sheetTitle = "%<\\AcSm SheetSet.Title>%";
string sheetNumber = "%<\\AcSm Sheet.Number>%";

// Diesel expression
string dieselField = "%<\\AcDiesel $(getvar,dwgname)>%";
```

## Embedding Fields in MText

```csharp
MText mtext = new MText();
// Embed a field in MText content using field code syntax
mtext.Contents = "Area: %<\\AcObjProp Object(%<\\_ObjId "
    + entity.Handle + ">%).Area \\f \"%lu2%pr2\">%";
```

## FieldCodeWithChildren

For managing nested/compound fields. **Implements `IDisposable` — always `Dispose()` when done.**

```csharp
using (FieldCodeWithChildren fcc = field.GetFieldCodeWithChildren())
{
    string code = fcc.FieldCode;
    Field[] children = fcc.Children;

    // Modify
    fcc.FieldCode = "new field code";
    fcc.Add(0, childField);  // add child at index

    field.SetFieldCodeWithChildren(fcc);
}  // Dispose() called automatically
```

## Evaluation Status

```csharp
FieldEvaluationStatusResult status = field.EvaluationStatus;
FieldEvaluationStatus evalStatus = status.Status;
int errorCode = status.ErrorCode;
string errorMsg = status.ErrorMessage;

// Construct status manually
var result = new FieldEvaluationStatusResult(
    FieldEvaluationStatus.Success, 0, "");
```

## Enums

**FieldEvaluationOptions** (flags):
Disable=0, OnOpen=1, OnSave=2, OnPlot=4, OnEtransmit=8, OnRegen=16, OnDemand=32, Automatic=63

**FieldEvaluationStatus:**
NotYetEvaluated=1, Success=2, EvaluatorNotFound=4, SyntaxError=8, InvalidCode=16, InvalidContext=32, OtherError=64

**FieldEvaluationContext:**
Open=1, Save=2, Plot=4, Etransmit=8, Regen=16, Demand=32, Preview=64

**FieldState** (flags):
Initialized=1, Compiled=2, Modified=4, Evaluated=8, HasCache=16, HasFormattedString=32

**FieldCodeFlags** (flags):
FieldCode=1, EvaluatedText=2, EvaluatedChildren=4, ObjectReference=8, AddMarkers=16, EscapeBackslash=32, StripOptions=64, PreserveFields=128, TextField=256

**FieldFilingOptions** (flags):
SkipFilingResult=1

## Gotchas

- Field codes use `%<` and `>%` as delimiters - these MUST be present
- Object references in field codes use Handle values (not ObjectId) - handles are persistent across sessions, ObjectIds are not
- `Evaluate()` must be called explicitly for programmatically created fields; automatic evaluation only happens based on `EvaluationOption` triggers
- `ConvertToTextField()` permanently freezes the field - it cannot be converted back to a dynamic field
- Field codes are case-sensitive for evaluator names (`\\AcVar`, `\\AcObjProp`, `\\AcExpr`, etc.)
- Nested fields (fields within field codes) use `%<\\_ObjId>%` syntax for object references
- `GetFieldCode()` without flags returns the raw field code; use `FieldCodeFlags.EvaluatedText` to get the current display value
- The `\\f` format specifier in field codes uses AutoCAD format strings, not .NET format strings

## Related Skills

- `acad-mtext` — embedding fields in MText content
- `acad-tables` — field content in table cells
- `acad-blocks` — embedding fields in attribute definitions