Leader Class

Overview

The Leader class represents a leader annotation entity in AutoCAD. A leader is a line or spline with an arrowhead that connects annotation text or blocks to specific features in a drawing. Leaders are commonly used for callouts, notes, and dimensional annotations.

Namespace

Autodesk.AutoCAD.DatabaseServices

Inheritance Hierarchy

System.Object
  └─ RXObject
      └─ DBObject
          └─ Entity
              └─ Curve
                  └─ Leader

Key Properties

Property	Type	Description
`HasArrowHead`	`bool`	Gets/sets whether the leader has an arrowhead
`HasHookLine`	`bool`	Gets/sets whether the leader has a hook line
`IsSplined`	`bool`	Gets/sets whether the leader is splined
`Annotation`	`ObjectId`	Gets/sets the annotation object (text, block, etc.)
`DimStyle`	`ObjectId`	Gets/sets the dimension style
`DimScale`	`double`	Gets/sets the dimension scale
`ColorIndex`	`short`	Gets/sets the color index
`NumVertices`	`int`	Gets the number of vertices

Key Methods

Method	Return Type	Description
`AppendVertex(Point3d)`	`void`	Adds a vertex to the leader
`GetVertexAt(int)`	`Point3d`	Gets the vertex at the specified index
`SetVertexAt(int, Point3d)`	`void`	Sets the vertex at the specified index
`RemoveLastVertex()`	`void`	Removes the last vertex
`EvaluateLeader()`	`void`	Recalculates the leader geometry
`AttachAnnotation(ObjectId)`	`void`	Attaches an annotation to the leader

Code Examples

Example 1: Creating a Simple Leader

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
    
    // Create leader
    Leader leader = new Leader();
    leader.SetDatabaseDefaults();
    
    // Add vertices (from annotation point to feature)
    leader.AppendVertex(new Point3d(10, 10, 0)); // Annotation point
    leader.AppendVertex(new Point3d(5, 5, 0));   // Elbow point
    leader.AppendVertex(new Point3d(0, 0, 0));   // Feature point (arrowhead)
    
    // Set properties
    leader.HasArrowHead = true;
    leader.ColorIndex = 1; // Red
    
    // Add to drawing
    btr.AppendEntity(leader);
    tr.AddNewlyCreatedDBObject(leader, true);
    
    // Evaluate to update geometry
    leader.EvaluateLeader();
    
    tr.Commit();
}

Example 2: Creating Leader with Text Annotation

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
    
    // Create text annotation
    MText mtext = new MText();
    mtext.SetDatabaseDefaults();
    mtext.Location = new Point3d(10, 10, 0);
    mtext.Contents = "This is a note";
    mtext.TextHeight = 2.5;
    
    ObjectId mtextId = btr.AppendEntity(mtext);
    tr.AddNewlyCreatedDBObject(mtext, true);
    
    // Create leader
    Leader leader = new Leader();
    leader.SetDatabaseDefaults();
    leader.AppendVertex(new Point3d(10, 10, 0));
    leader.AppendVertex(new Point3d(5, 5, 0));
    leader.AppendVertex(new Point3d(0, 0, 0));
    leader.HasArrowHead = true;
    
    // Attach annotation
    leader.Annotation = mtextId;
    
    btr.AppendEntity(leader);
    tr.AddNewlyCreatedDBObject(leader, true);
    leader.EvaluateLeader();
    
    tr.Commit();
}

Example 3: Creating Splined Leader

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
    
    Leader leader = new Leader();
    leader.SetDatabaseDefaults();
    
    // Add multiple vertices for smooth curve
    leader.AppendVertex(new Point3d(15, 15, 0));
    leader.AppendVertex(new Point3d(12, 10, 0));
    leader.AppendVertex(new Point3d(8, 8, 0));
    leader.AppendVertex(new Point3d(5, 5, 0));
    leader.AppendVertex(new Point3d(0, 0, 0));
    
    // Make it splined
    leader.IsSplined = true;
    leader.HasArrowHead = true;
    leader.ColorIndex = 3; // Green
    
    btr.AppendEntity(leader);
    tr.AddNewlyCreatedDBObject(leader, true);
    leader.EvaluateLeader();
    
    tr.Commit();
}

Example 4: Reading Leader Properties

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Leader leader = tr.GetObject(leaderId, OpenMode.ForRead) as Leader;
    
    ed.WriteMessage("\n=== Leader Information ===");
    ed.WriteMessage($"\nHas Arrowhead: {leader.HasArrowHead}");
    ed.WriteMessage($"\nHas Hook Line: {leader.HasHookLine}");
    ed.WriteMessage($"\nIs Splined: {leader.IsSplined}");
    ed.WriteMessage($"\nNumber of Vertices: {leader.NumVertices}");
    ed.WriteMessage($"\nAnnotation: {leader.Annotation}");
    
    ed.WriteMessage("\n\nVertices:");
    for (int i = 0; i < leader.NumVertices; i++)
    {
        Point3d vertex = leader.GetVertexAt(i);
        ed.WriteMessage($"\n  Vertex {i}: ({vertex.X:F2}, {vertex.Y:F2}, {vertex.Z:F2})");
    }
    
    tr.Commit();
}

Example 5: Modifying Leader Vertices

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Leader leader = tr.GetObject(leaderId, OpenMode.ForWrite) as Leader;
    
    // Move the middle vertex
    if (leader.NumVertices >= 3)
    {
        Point3d middleVertex = leader.GetVertexAt(1);
        Point3d newVertex = new Point3d(middleVertex.X + 5, middleVertex.Y + 5, middleVertex.Z);
        leader.SetVertexAt(1, newVertex);
        
        leader.EvaluateLeader();
    }
    
    tr.Commit();
}

Example 6: Leader with Block Annotation

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTable bt = tr.GetObject(db.BlockTableId, OpenMode.ForRead) as BlockTable;
    BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
    
    // Create block reference (assuming "DetailCallout" block exists)
    if (bt.Has("DetailCallout"))
    {
        BlockReference blockRef = new BlockReference(new Point3d(10, 10, 0), bt["DetailCallout"]);
        blockRef.SetDatabaseDefaults();
        
        ObjectId blockRefId = btr.AppendEntity(blockRef);
        tr.AddNewlyCreatedDBObject(blockRef, true);
        
        // Create leader
        Leader leader = new Leader();
        leader.SetDatabaseDefaults();
        leader.AppendVertex(new Point3d(10, 10, 0));
        leader.AppendVertex(new Point3d(5, 5, 0));
        leader.AppendVertex(new Point3d(0, 0, 0));
        leader.HasArrowHead = true;
        leader.Annotation = blockRefId;
        
        btr.AppendEntity(leader);
        tr.AddNewlyCreatedDBObject(leader, true);
        leader.EvaluateLeader();
    }
    
    tr.Commit();
}

Example 7: Setting Leader Dimension Style

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Leader leader = tr.GetObject(leaderId, OpenMode.ForWrite) as Leader;
    
    // Get dimension style table
    DimStyleTable dst = tr.GetObject(db.DimStyleTableId, OpenMode.ForRead) as DimStyleTable;
    
    if (dst.Has("Annotative"))
    {
        leader.DimStyle = dst["Annotative"];
        leader.EvaluateLeader();
        
        ed.WriteMessage("\nApplied 'Annotative' dimension style");
    }
    
    tr.Commit();
}

Example 8: Creating Multiple Leaders

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
    
    Point3d centerPoint = new Point3d(0, 0, 0);
    int numLeaders = 8;
    double radius = 10.0;
    
    for (int i = 0; i < numLeaders; i++)
    {
        double angle = (i * 2 * Math.PI) / numLeaders;
        Point3d endPoint = new Point3d(
            centerPoint.X + radius * Math.Cos(angle),
            centerPoint.Y + radius * Math.Sin(angle),
            0
        );
        
        Leader leader = new Leader();
        leader.SetDatabaseDefaults();
        leader.AppendVertex(endPoint);
        leader.AppendVertex(new Point3d(
            centerPoint.X + (radius * 0.5) * Math.Cos(angle),
            centerPoint.Y + (radius * 0.5) * Math.Sin(angle),
            0
        ));
        leader.AppendVertex(centerPoint);
        leader.HasArrowHead = true;
        leader.ColorIndex = (short)(i % 7 + 1);
        
        btr.AppendEntity(leader);
        tr.AddNewlyCreatedDBObject(leader, true);
        leader.EvaluateLeader();
    }
    
    ed.WriteMessage($"\nCreated {numLeaders} leaders");
    
    tr.Commit();
}

Best Practices

Call EvaluateLeader(): Always call after creating or modifying leader
Vertex Order: First vertex is annotation point, last is arrowhead point
Minimum Vertices: Need at least 2 vertices for a valid leader
Annotation Attachment: Attach annotation for automatic positioning
Dimension Styles: Use dimension styles for consistent appearance
Splined Leaders: Use for curved, organic-looking leaders
Hook Lines: Enable for horizontal landing line at annotation
Color and Linetype: Set explicitly for visibility

Leader vs MLeader

Feature	Leader	MLeader
Introduction	Legacy (R13+)	Modern (2008+)
Flexibility	Basic	Advanced
Multiple Leaders	No	Yes
Content Types	Limited	Text, Block, None
Styles	Dimension Style	MLeader Style
Recommended	Legacy compatibility	New drawings

Common Use Cases

Callouts: Identifying features in drawings
Notes: Adding explanatory text
Detail References: Pointing to detail views
Dimension Annotations: Supplemental dimensional information
Part Labels: Identifying components

Related Objects

MLeader - Modern multi-leader annotation
Dimension - Dimension annotation base class
Curve - Base class for Leader
Entity - Base class for all entities
MText - Text annotation for leaders
BlockReference - Block annotation for leaders

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Leader Class

Overview

Namespace

Inheritance Hierarchy

Key Properties

Key Methods

Code Examples

Example 1: Creating a Simple Leader

Example 2: Creating Leader with Text Annotation

Example 3: Creating Splined Leader

Example 4: Reading Leader Properties

Example 5: Modifying Leader Vertices

Example 6: Leader with Block Annotation

Example 7: Setting Leader Dimension Style

Example 8: Creating Multiple Leaders

Best Practices

Leader vs MLeader

Common Use Cases

Related Objects

References

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Leader.md

Latest commit

History

Leader.md

File metadata and controls

Leader Class

Overview

Namespace

Inheritance Hierarchy

Key Properties

Key Methods

Code Examples

Example 1: Creating a Simple Leader

Example 2: Creating Leader with Text Annotation

Example 3: Creating Splined Leader

Example 4: Reading Leader Properties

Example 5: Modifying Leader Vertices

Example 6: Leader with Block Annotation

Example 7: Setting Leader Dimension Style

Example 8: Creating Multiple Leaders

Best Practices

Leader vs MLeader

Common Use Cases

Related Objects

References