Acad Mleaders

AutoCAD Multileaders (MLeader)

Use this skill when creating or modifying multileader objects - leaders with text, block, or tolerance content.

MLeader Structure

MLeader
├── Leader 0
│   ├── LeaderLine 0 (vertices: first → ... → last/arrow)
│   └── LeaderLine 1
├── Leader 1
│   └── LeaderLine 0
└── Content (MText, Block, or Tolerance - shared across all leaders)

An MLeader contains one or more Leaders (collections of leader lines pointing to the same content side). Each Leader contains one or more LeaderLines, each with multiple Vertices. The first vertex is the landing/connection point near content; the last vertex is the arrow tip.

Creating an MLeader with MText Content

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = (BlockTableRecord)tr.GetObject(
        db.CurrentSpaceId, OpenMode.ForWrite);

    MLeader mleader = new MLeader();
    mleader.SetDatabaseDefaults();

    // Set content type
    mleader.ContentType = ContentType.MTextContent;

    // Create MText content
    MText mt = new MText();
    mt.Contents = "Label Text";
    mt.TextHeight = 2.5;
    mleader.MText = mt;

    // Add a leader with one leader line
    int leaderIdx = mleader.AddLeader();
    int lineIdx = mleader.AddLeaderLine(leaderIdx);

    // Add vertices (last = arrow tip, first = near content)
    mleader.AddFirstVertex(lineIdx, new Point3d(200, 200, 0));
    mleader.AddLastVertex(lineIdx, new Point3d(100, 100, 0));

    // Set text location
    mleader.TextLocation = new Point3d(210, 200, 0);

    btr.AppendEntity(mleader);
    tr.AddNewlyCreatedDBObject(mleader, true);
    tr.Commit();
}

Creating an MLeader with Block Content

MLeader mleader = new MLeader();
mleader.SetDatabaseDefaults();
mleader.ContentType = ContentType.BlockContent;
mleader.BlockContentId = blockDefId;  // ObjectId of BlockTableRecord
mleader.BlockPosition = new Point3d(200, 200, 0);
mleader.BlockScale = new Scale3d(1.0);
mleader.BlockRotation = 0.0;
mleader.BlockColor = Color.FromColorIndex(ColorMethod.ByLayer, 256);
mleader.BlockConnectionType = BlockConnectionType.ConnectExtents;
// or BlockConnectionType.ConnectBase

int leaderIdx = mleader.AddLeader();
int lineIdx = mleader.AddLeaderLine(leaderIdx);
mleader.AddFirstVertex(lineIdx, new Point3d(200, 200, 0));
mleader.AddLastVertex(lineIdx, new Point3d(100, 100, 0));

Leader and LeaderLine Management

// Add leaders and lines
int leaderIdx = mleader.AddLeader();
int lineIdx = mleader.AddLeaderLine(leaderIdx);
// or: int lineIdx = mleader.AddLeaderLine(new Point3d(x, y, z)); // adds to default leader

// Get all leader/line indexes
ArrayList leaderIndexes = mleader.GetLeaderIndexes();
ArrayList lineIndexes = mleader.GetLeaderLineIndexes(leaderIdx);

// Get parent leader of a line
int parentLeader = mleader.GetLeaderIndex(lineIdx);

// Remove
mleader.RemoveLeaderLine(lineIdx);
mleader.RemoveLeader(leaderIdx);

Vertex Management

// Add vertices
mleader.AddFirstVertex(lineIdx, connectionPoint);  // near content
mleader.AddLastVertex(lineIdx, arrowPoint);         // arrow tip

// Get/set vertices
Point3d first = mleader.GetFirstVertex(lineIdx);
Point3d last = mleader.GetLastVertex(lineIdx);
mleader.SetFirstVertex(lineIdx, newPoint);
mleader.SetLastVertex(lineIdx, newPoint);

// Middle vertices
int count = mleader.VerticesCount(lineIdx);
Point3d pt = mleader.GetVertex(lineIdx, 1);  // 0-indexed
mleader.SetVertex(lineIdx, 1, newPoint);

// Remove vertices
mleader.RemoveFirstVertex(lineIdx);
mleader.RemoveLastVertex(lineIdx);

Per-Leader and Per-Line Overrides

// Dogleg per leader
mleader.SetDogleg(leaderIdx, new Vector3d(1, 0, 0));
Vector3d dogDir = mleader.GetDogleg(leaderIdx);
mleader.SetDoglegLength(leaderIdx, 5.0);
double dogLen = mleader.GetDoglegLength(leaderIdx);

// Per-line leader appearance overrides
mleader.SetLeaderLineType(lineIdx, LeaderType.SplineLeader);
mleader.SetLeaderLineColor(lineIdx, Color.FromColorIndex(ColorMethod.ByAci, 1));
mleader.SetLeaderLineWeight(lineIdx, LineWeight.LineWeight050);
mleader.SetArrowSymbolId(lineIdx, arrowBlockId);
mleader.SetArrowSize(lineIdx, 3.0);

// Read overrides
LeaderType lt = mleader.GetLeaderLineType(lineIdx);
Color lc = mleader.GetLeaderLineColor(lineIdx);

Text Attachment (per direction)

// Set attachment type for specific leader direction
mleader.SetTextAttachmentType(
    TextAttachmentType.AttachmentMiddle,
    LeaderDirectionType.LeftLeader);

TextAttachmentType att = mleader.GetTextAttachmentType(
    LeaderDirectionType.RightLeader);

Block Attributes

// Read/write attributes on block content
AttributeReference attRef = mleader.GetBlockAttribute(attDefId);
string val = attRef.TextString;

attRef.TextString = "New Value";
mleader.SetBlockAttribute(attDefId, attRef);

Movement

// Move entire MLeader
mleader.MoveMLeader(new Vector3d(50, 50, 0), MoveType.MoveAllPoints);

MoveType enum: MoveAllPoints=0, MoveAllExceptArrowHeaderPoints=1, MoveContentAndDoglegPoints=2

MLeaderStyle

// Create a new style
MLeaderStyle style = new MLeaderStyle();
// or copy: new MLeaderStyle(existingStyle);

style.Name = "My Leader Style";
style.ContentType = ContentType.MTextContent;
style.TextHeight = 2.5;
style.TextStyleId = textStyleId;
style.TextColor = Color.FromColorIndex(ColorMethod.ByLayer, 256);
style.TextAlignmentType = TextAlignmentType.LeftAlignment;
style.TextAlignAlwaysLeft = false;
style.TextAngleType = TextAngleType.HorizontalAngle;
style.EnableFrameText = false;

// Leader line settings
style.LeaderLineType = LeaderType.StraightLeader;
style.LeaderLineColor = Color.FromColorIndex(ColorMethod.ByBlock, 0);
style.ArrowSymbolId = ObjectId.Null;  // default arrow
style.ArrowSize = 3.0;
style.EnableDogleg = true;
style.DoglegLength = 8.0;
style.EnableLanding = true;
style.LandingGap = 2.0;
style.ExtendLeaderToText = true;

// Block content defaults
style.BlockId = blockId;
style.BlockConnectionType = BlockConnectionType.ConnectExtents;
style.BlockScale = new Scale3d(1.0);
style.EnableBlockScale = false;
style.EnableBlockRotation = false;

// Workflow
style.Scale = 1.0;
style.BreakSize = 2.0;
style.MaxLeaderSegmentsPoints = 2;
style.FirstSegmentAngleConstraint = AngleConstraint.DegreesAny;
style.SecondSegmentAngleConstraint = AngleConstraint.DegreesAny;
style.DrawLeaderOrderType = DrawLeaderOrderType.DrawLeaderHeadFirst;
style.DrawMLeaderOrderType = DrawMLeaderOrderType.DrawContentFirst;

// Text attachment per direction
style.SetTextAttachmentType(
    TextAttachmentType.AttachmentMiddleOfTop, LeaderDirectionType.LeftLeader);
style.SetTextAttachmentType(
    TextAttachmentType.AttachmentMiddleOfTop, LeaderDirectionType.RightLeader);
style.TextAttachmentDirection = TextAttachmentDirection.AttachmentHorizontal;

// Post to database
ObjectId styleId = style.PostMLeaderStyleToDb(db, "My Leader Style");
tr.AddNewlyCreatedDBObject(style, true);

Enums

TextAttachmentType: AttachmentTopOfTop=0, AttachmentMiddleOfTop=1, AttachmentMiddle=2, AttachmentMiddleOfBottom=3, AttachmentBottomOfBottom=4, AttachmentBottomLine=5, AttachmentBottomOfTopLine=6, AttachmentBottomOfTop=7, AttachmentAllLine=8, AttachmentCenter=9, AttachmentLinedCenter=10

LeaderDirectionType: UnknownLeader=0, LeftLeader=1, RightLeader=2, TopLeader=3, BottomLeader=4

AngleConstraint: DegreesAny=0, Degrees015=1, Degrees030=2, Degrees045=3, Degrees060=4, Degrees090=6, DegreesHorz=12

DrawLeaderOrderType: DrawLeaderHeadFirst=0, DrawLeaderTailFirst=1

DrawMLeaderOrderType: DrawContentFirst=0, DrawLeaderFirst=1

Legacy Leader Class

The OARX guide documents the older Leader class (not MLeader). Prefer MLeader for new code. Use Leader only when working with legacy drawings that contain it.

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = (BlockTableRecord)tr.GetObject(
        db.CurrentSpaceId, OpenMode.ForWrite);

    Leader leader = new Leader();
    leader.SetDatabaseDefaults();

    // Add vertices (start at arrow tip, end at annotation)
    leader.AppendVertex(new Point3d(100, 100, 0));  // arrow tip
    leader.AppendVertex(new Point3d(200, 150, 0));  // elbow
    leader.AppendVertex(new Point3d(250, 150, 0));  // near annotation

    leader.HasArrowHead = true;
    leader.IsSplined = false;

    btr.AppendEntity(leader);
    tr.AddNewlyCreatedDBObject(leader, true);

    // Attach annotation (must be added to DB first)
    MText mt = new MText();
    mt.Location = new Point3d(252, 150, 0);
    mt.Contents = "Leader Text";
    mt.TextHeight = 2.5;
    btr.AppendEntity(mt);
    tr.AddNewlyCreatedDBObject(mt, true);

    leader.Annotation = mt.ObjectId;  // attach annotation
    leader.EvaluateLeader();          // MUST call to update hook geometry

    tr.Commit();
}

Gotchas

• Leader/line indexes are NOT sequential integers - always use GetLeaderIndexes() and GetLeaderLineIndexes() to get valid indexes
• First vertex = connection point near content; Last vertex = arrow tip (opposite of what you might expect)
• AddLeaderLine(Point3d) adds a line to a default leader; AddLeaderLine(int leaderIndex) adds to a specific leader - different signatures do different things
• Setting MText property replaces the content object entirely; modify the existing MText object for incremental changes
• Per-line overrides (color, weight, arrow) only take effect if they differ from the MLeader's default properties
• MLeaderStyle must be posted to the database with PostMLeaderStyleToDb() before it can be assigned to an MLeader
• MoveType.MoveAllExceptArrowHeaderPoints keeps arrow tips fixed while moving content - useful for repositioning text without changing what the leader points to
• TextAttachmentType and direction interact: horizontal leaders use top/middle/bottom attachment; vertical leaders use center/lined attachment

Related Skills

• acad-mtext — MText as MLeader text content
• acad-blocks — block references as MLeader block content
• acad-geometry — Point3d for leader vertices and attachment points