Locking and unlocking AutoCAD layers visibly using .NET

On Friday I visited Munich Airport: not only to catch a flight home to Switzerland but also to take a look at some AutoCAD issues frustrating the developers working on the airport’s facilities management system. During the course of the day we were able to work through a number of problems – such as using COM (SendCommand()) to run a script synchronously as well as to get the fill pattern for MPolygon objects (this is apparently broken in .NET) – but there was one I had to bring home with me: when locking and unlocking layers programmatically, their geometry doesn’t fade and unfade despite LAYLOCKFADECTL being set correctly.

I found a few instances of this reported on the web, but I didn’t come across a solution. After some work I found that if you set the IsOff property (or even IsFrozen, although I didn’t actually try this) on the layer that’s being locked/unlocked, then it’s enough to trigger the layer change that can be picked up by Editor.ApplyCurDwgLayerTableChanges() (and then Editor.Regen()).

So yes, we’re turning it off and on again. Sort of: we don’t actually need to toggle IsOff – we can just set it to the current property value.

Here’s the C# code implementing our LL (LockLayers) and UL (UnlockLayers) commands:

using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Runtime;
 
namespace LayerManipulation
{
  public static class Extensions
  {
    public static void LockOrUnlockAllLayers(
      this Document doc, bool dolock, bool lockZero = false
    )
    {
      var db = doc.Database;
      var ed = doc.Editor;
 
      using (var tr = db.TransactionManager.StartTransaction())
      {
        var lt = (LayerTable)tr.GetObject(db.LayerTableId, OpenMode.ForRead);
        foreach (var ltrId in lt)
        {
          // Don't try to lock/unlock either the current layer or layer 0
          // (depending on whether lockZero == true for the latter)
 
          if (ltrId != db.Clayer && (lockZero || ltrId != db.LayerZero))
          {
            // Open the layer for write and lock/unlock it
 
            var ltr = (LayerTableRecord)tr.GetObject(ltrId, OpenMode.ForWrite);
            ltr.IsLocked = dolock;
            ltr.IsOff = ltr.IsOff; // This is needed to force a graphics update
          }
        }
        tr.Commit();
      }
 
      // These two calls will result in the layer's geometry fading/unfading
      // appropriately
 
      ed.ApplyCurDwgLayerTableChanges();
      ed.Regen();
    }
  }
 
  public class Commands
  {
    [CommandMethod("LL")]
    public void LockLayers()
    {
      var doc = Application.DocumentManager.MdiActiveDocument;
      if (doc == null) return;
 
      doc.LockOrUnlockAllLayers(true);
    }
 
    [CommandMethod("UL")]
    public void UnlockLayers()
    {
      var doc = Application.DocumentManager.MdiActiveDocument;
      if (doc == null) return;
 
      doc.LockOrUnlockAllLayers(false);
    }
  }
}
 