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Group.md

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Group

Namespace: Autodesk.AutoCAD.DatabaseServices
Assembly: AcDbMgd.dll

Overview

The Group class represents a named collection of entities that can be selected and manipulated as a single unit. Groups provide a way to organize related objects without creating a block.

Key Concept: Groups are like selection sets that persist in the drawing. Unlike blocks, grouped entities maintain their individual properties and can be edited independently.

Class Hierarchy

Object
  └─ RXObject
      └─ DBObject
          └─ Group

Key Properties

Property Type Description
Name string Gets/sets the group name
Description string Gets/sets the group description
Selectable bool Gets/sets whether group can be selected as unit
IsAnonymous bool Checks if group is anonymous (unnamed)
NumEntities int Gets the number of entities in group

Key Methods

Method Return Type Description
Append(ObjectId) void Adds entity to group
Remove(ObjectId) void Removes entity from group
GetAllEntityIds() ObjectId[] Gets all entity IDs in group
Has(ObjectId) bool Checks if entity is in group
Clear() void Removes all entities from group

Common Usage Patterns

1. Creating a Group

using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Runtime;

[CommandMethod("CREATEGROUP")]
public void CreateGroup()
{
    Document doc = Application.DocumentManager.MdiActiveDocument;
    Database db = doc.Database;
    Editor ed = doc.Editor;
    
    // Prompt for group name
    PromptStringOptions pso = new PromptStringOptions("\nEnter group name: ");
    pso.AllowSpaces = false;
    PromptResult pr = ed.GetString(pso);
    if (pr.Status != PromptStatus.OK) return;
    
    string groupName = pr.StringResult;
    
    // Select entities
    PromptSelectionResult psr = ed.GetSelection();
    if (psr.Status != PromptStatus.OK) return;
    
    using (Transaction tr = db.TransactionManager.StartTransaction())
    {
        DBDictionary groupDict = tr.GetObject(db.GroupDictionaryId, 
            OpenMode.ForWrite) as DBDictionary;
        
        // Create new group
        Group group = new Group("Group description", true);
        group.Name = groupName;
        
        // Add to group dictionary
        groupDict.SetAt(groupName, group);
        tr.AddNewlyCreatedDBObject(group, true);
        
        // Add entities to group
        foreach (SelectedObject so in psr.Value)
        {
            group.Append(so.ObjectId);
        }
        
        tr.Commit();
        ed.WriteMessage($"\nGroup '{groupName}' created with {group.NumEntities} entities");
    }
}

2. Listing All Groups

[CommandMethod("LISTGROUPS")]
public void ListAllGroups()
{
    Document doc = Application.DocumentManager.MdiActiveDocument;
    Database db = doc.Database;
    Editor ed = doc.Editor;
    
    using (Transaction tr = db.TransactionManager.StartTransaction())
    {
        DBDictionary groupDict = tr.GetObject(db.GroupDictionaryId, 
            OpenMode.ForRead) as DBDictionary;
        
        ed.WriteMessage("\n=== Groups ===");
        
        foreach (DBDictionaryEntry entry in groupDict)
        {
            Group group = tr.GetObject(entry.Value, OpenMode.ForRead) as Group;
            
            ed.WriteMessage($"\n\nName: {group.Name}");
            ed.WriteMessage($"\n  Description: {group.Description}");
            ed.WriteMessage($"\n  Entities: {group.NumEntities}");
            ed.WriteMessage($"\n  Selectable: {group.Selectable}");
            ed.WriteMessage($"\n  Anonymous: {group.IsAnonymous}");
        }
        
        tr.Commit();
    }
}

3. Adding Entities to Existing Group

[CommandMethod("ADDTOGROUP")]
public void AddEntitiesToGroup()
{
    Document doc = Application.DocumentManager.MdiActiveDocument;
    Database db = doc.Database;
    Editor ed = doc.Editor;
    
    // Prompt for group name
    PromptStringOptions pso = new PromptStringOptions("\nEnter group name: ");
    PromptResult pr = ed.GetString(pso);
    if (pr.Status != PromptStatus.OK) return;
    
    string groupName = pr.StringResult;
    
    // Select entities to add
    PromptSelectionResult psr = ed.GetSelection();
    if (psr.Status != PromptStatus.OK) return;
    
    using (Transaction tr = db.TransactionManager.StartTransaction())
    {
        DBDictionary groupDict = tr.GetObject(db.GroupDictionaryId, 
            OpenMode.ForRead) as DBDictionary;
        
        if (!groupDict.Contains(groupName))
        {
            ed.WriteMessage($"\nGroup '{groupName}' not found");
            tr.Commit();
            return;
        }
        
        Group group = tr.GetObject(groupDict.GetAt(groupName), 
            OpenMode.ForWrite) as Group;
        
        int addedCount = 0;
        foreach (SelectedObject so in psr.Value)
        {
            if (!group.Has(so.ObjectId))
            {
                group.Append(so.ObjectId);
                addedCount++;
            }
        }
        
        tr.Commit();
        ed.WriteMessage($"\nAdded {addedCount} entities to group '{groupName}'");
    }
}

4. Removing Entities from Group

[CommandMethod("REMOVEFROMGROUP")]
public void RemoveEntitiesFromGroup()
{
    Document doc = Application.DocumentManager.MdiActiveDocument;
    Database db = doc.Database;
    Editor ed = doc.Editor;
    
    // Prompt for group name
    PromptStringOptions pso = new PromptStringOptions("\nEnter group name: ");
    PromptResult pr = ed.GetString(pso);
    if (pr.Status != PromptStatus.OK) return;
    
    string groupName = pr.StringResult;
    
    // Select entities to remove
    PromptSelectionResult psr = ed.GetSelection();
    if (psr.Status != PromptStatus.OK) return;
    
    using (Transaction tr = db.TransactionManager.StartTransaction())
    {
        DBDictionary groupDict = tr.GetObject(db.GroupDictionaryId, 
            OpenMode.ForRead) as DBDictionary;
        
        if (!groupDict.Contains(groupName))
        {
            ed.WriteMessage($"\nGroup '{groupName}' not found");
            tr.Commit();
            return;
        }
        
        Group group = tr.GetObject(groupDict.GetAt(groupName), 
            OpenMode.ForWrite) as Group;
        
        int removedCount = 0;
        foreach (SelectedObject so in psr.Value)
        {
            if (group.Has(so.ObjectId))
            {
                group.Remove(so.ObjectId);
                removedCount++;
            }
        }
        
        tr.Commit();
        ed.WriteMessage($"\nRemoved {removedCount} entities from group '{groupName}'");
    }
}

5. Selecting All Entities in Group

[CommandMethod("SELECTGROUP")]
public void SelectEntitiesInGroup()
{
    Document doc = Application.DocumentManager.MdiActiveDocument;
    Database db = doc.Database;
    Editor ed = doc.Editor;
    
    // Prompt for group name
    PromptStringOptions pso = new PromptStringOptions("\nEnter group name: ");
    PromptResult pr = ed.GetString(pso);
    if (pr.Status != PromptStatus.OK) return;
    
    string groupName = pr.StringResult;
    
    using (Transaction tr = db.TransactionManager.StartTransaction())
    {
        DBDictionary groupDict = tr.GetObject(db.GroupDictionaryId, 
            OpenMode.ForRead) as DBDictionary;
        
        if (!groupDict.Contains(groupName))
        {
            ed.WriteMessage($"\nGroup '{groupName}' not found");
            tr.Commit();
            return;
        }
        
        Group group = tr.GetObject(groupDict.GetAt(groupName), 
            OpenMode.ForRead) as Group;
        
        ObjectId[] entityIds = group.GetAllEntityIds();
        
        // Create selection set
        ed.SetImpliedSelection(entityIds);
        
        ed.WriteMessage($"\nSelected {entityIds.Length} entities from group '{groupName}'");
        tr.Commit();
    }
}

6. Deleting Group

[CommandMethod("DELETEGROUP")]
public void DeleteGroup()
{
    Document doc = Application.DocumentManager.MdiActiveDocument;
    Database db = doc.Database;
    Editor ed = doc.Editor;
    
    // Prompt for group name
    PromptStringOptions pso = new PromptStringOptions("\nEnter group name to delete: ");
    PromptResult pr = ed.GetString(pso);
    if (pr.Status != PromptStatus.OK) return;
    
    string groupName = pr.StringResult;
    
    using (Transaction tr = db.TransactionManager.StartTransaction())
    {
        DBDictionary groupDict = tr.GetObject(db.GroupDictionaryId, 
            OpenMode.ForWrite) as DBDictionary;
        
        if (!groupDict.Contains(groupName))
        {
            ed.WriteMessage($"\nGroup '{groupName}' not found");
            tr.Commit();
            return;
        }
        
        Group group = tr.GetObject(groupDict.GetAt(groupName), 
            OpenMode.ForWrite) as Group;
        
        // Erase the group (entities remain in drawing)
        group.Erase();
        
        ed.WriteMessage($"\nGroup '{groupName}' deleted (entities preserved)");
        tr.Commit();
    }
}

Best Practices

  1. Unique Names: Use descriptive, unique group names
  2. Selectable Flag: Set Selectable to true for user interaction
  3. Description: Provide clear descriptions
  4. Check Membership: Use Has() before removing entities
  5. Preserve Entities: Deleting group doesn't delete entities
  6. Anonymous Groups: Use for temporary grouping

Related Classes

See Also