You can iterate through the Layers and Linetypes tables to find all the layers and linetypes in a drawing.
The following example iterates through the Layers table to gather the names of all the layers in the drawing. The names are then displayed in a message box.
using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
[CommandMethod("DisplayLayerNames")]
public static void DisplayLayerNames()
{
// Get the current document and database
Document acDoc = Application.DocumentManager.MdiActiveDocument;
Database acCurDb = acDoc.Database;
// Start a transaction
using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())
{
// Open the Layer table for read
LayerTable acLyrTbl;
acLyrTbl = acTrans.GetObject(acCurDb.LayerTableId,
OpenMode.ForRead) as LayerTable;
string sLayerNames = "";
foreach (ObjectId acObjId in acLyrTbl)
{
LayerTableRecord acLyrTblRec;
acLyrTblRec = acTrans.GetObject(acObjId,
OpenMode.ForRead) as LayerTableRecord;
sLayerNames = sLayerNames + "\n" + acLyrTblRec.Name;
}
Application.ShowAlertDialog("The layers in this drawing are: " +
sLayerNames);
// Dispose of the transaction
}
}