Preventing AutoCAD objects from being highlighted using .NET

Thanks to Balaji Ramamoorthy, from DevTech India, for the basis of this post (some code he provided in a recent reply to an ADN member).

The original question came from someone who wanted to stop text objects from being highlighted when selected. I’ve extended the mechanism to make it a little more flexible: it now maintains a list of object types (their DXF names) of objects that should not be highlighted, when selected.

Balaji implemented a HighlightOverrule to control the highlighting. This doesn’t stop the objects from actually being selected, however: in the next post I’ll add some additional code from Balaji’s implementation that also stops the objects from being selected.

Here’s the C# code:

using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Runtime;
using System.Collections.Generic;
using System.Text;
 
namespace PreventSelectionHighlight
{
  public class Test : IExtensionApplication
  {
    static UnhighlightOverrule _ho = new UnhighlightOverrule();
 
    [CommandMethod("UH")]
    public static void Unhighlight()
    {
      Document doc = Application.DocumentManager.MdiActiveDocument;
      Editor ed = doc.Editor;
 
      // Print the list of currently unhighlighted classes
 
      ed.WriteMessage(_ho.ListToPrint());
 
      // Get the type to add to the list
 
      PromptResult pr =
        ed.GetString(
          "\nEnter the type of object to stop from " +
          "being highlighted: "
        );
      if (pr.Status != PromptStatus.OK)
        return;
 
      if (_ho.IsInList(pr.StringResult))
      {
        ed.WriteMessage("\nItem already in the list.");
      }
      else
      {
        _ho.AddToList(pr.StringResult);
        ed.WriteMessage("\nItem added to the list.");
      }
    }
 
    [CommandMethod("RH")]
    public static void Rehighlight()
    {
      Document doc = Application.DocumentManager.MdiActiveDocument;
      Editor ed = doc.Editor;
 
      // Print the list of currently unhighlighted classes
 
      ed.WriteMessage(_ho.ListToPrint());
 
      // Get the type to remove from the list
 
      PromptResult pr =
        ed.GetString(
          "\nEnter the type of object to remove from the " +
          "list: "
        );
      if (pr.Status != PromptStatus.OK)
        return;
 
      if (!_ho.IsInList(pr.StringResult))
      {
        ed.WriteMessage("\nItem not currently in the list.");
      }
      else
      {
        _ho.RemoveFromList(pr.StringResult);
        ed.WriteMessage("\nItem removed from the list.");
      }
    }
 
    void IExtensionApplication.Initialize()
    {
      // Add our overrule
 
      Overrule.AddOverrule(
        RXObject.GetClass(typeof(Entity)), _ho, false
      );
      Overrule.Overruling = true;
    }
 
    void IExtensionApplication.Terminate()
    {
      // Remove our overrule
 
      Overrule.RemoveOverrule(
        RXObject.GetClass(typeof(Entity)), _ho
      );
      Overrule.Overruling = false;
    }
  }
 
  class UnhighlightOverrule : HighlightOverrule
  {
    // The list of types to unhighlight
 
    List<string> _unhighlighted = new List<string>();
 
    // Add a type to the list
 
    public void AddToList(string name)
    {
      string upper = name.ToUpper();
      if (!_unhighlighted.Contains(upper))
      {
        _unhighlighted.Add(upper);
      }
    }
 
    // Remove a type from the list
 
    public void RemoveFromList(string name)
    {
      string upper = name.ToUpper();
      if (_unhighlighted.Contains(upper))
      {
        _unhighlighted.Remove(upper);
      }
    }
 
    // Check whether the list contains a type
 
    public bool IsInList(string name)
    {
      return _unhighlighted.Contains(name.ToUpper());
    }
 
    // Get a string printing the contents of the list
 
    public string ListToPrint()
    {
      string toPrint;
 
      if (_unhighlighted.Count == 0)
      {
        toPrint =
          "\nThere are currently no objects in the list " +
          "to stop from being highlighted.";
      }
      else
      {
        StringBuilder sb =
          new StringBuilder(
            "\nObjects of these types will not be highlighted " +
            "during selection:"
          );
        foreach (string name in _unhighlighted)
        {
          sb.Append(" " + name);
        }
        toPrint = sb.ToString();
      }
 
      return toPrint;
    }
 
    // Called when an entity is highlighted
 
    public override void Highlight(
      Entity entity, FullSubentityPath subId, bool highlightAll
    )
    {
      // If our object's type is in the list, return
      // without calling the base implementation
 
      if (IsInList(entity.GetRXClass().DxfName))
        return;
 
      base.Highlight(entity, subId, highlightAll);
    }
 
    // Called when an entity is unhighlighted
 
    public override void Unhighlight(
      Entity entity, FullSubentityPath subId, bool highlightAll
    )
    {
      base.Unhighlight(entity, subId, highlightAll);
    }
  }
}

You can use the UH command to “unhighlight” objects via their type’s DXF name and RH to re-highlight them.

Let’s draw some simple geometry – lines, arcs and circles.

When we select them, they all get highlighted (see? nothing up my sleeves. ;-)

Now we can use the UH command to stop lines and arcs from being highlighted:

Command: UH
There are currently no objects in the list to stop from being highlighted.
Enter the type of object to stop from being highlighted: line
Item added to the list.
Command: UH
Objects of these types will not be highlighted during selection:  LINE
Enter the type of object to stop from being highlighted: arc
Item added to the list.