Adding to the AutoCAD pickfirst set with .NET

January 30, 2007

Adding to the AutoCAD pickfirst set with .NET

Back in a much earlier post we looked at some code to access the pickfirst selection set.

I thought I'd now take a look at the more specific case of defining a command that adds entities into the current pickfirst selection set.

Here's some C# code I used to do this, with comments describing its behaviour. The most interesting point is that once we get the contents of the existing pickfirst set we then clear it and rehighlight the entities manually, to give the user a graphical clue of the previous contents.

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

namespace SelectionTest
{
  public class PickfirstTestCmds
  {
    [CommandMethod("PFA", CommandFlags.Modal |
                          CommandFlags.UsePickSet |
                          CommandFlags.Redraw)
    ]
    public void AddToPickfirstSet()
    {
      Document doc =
        Application.DocumentManager.MdiActiveDocument;

      Editor ed = doc.Editor;

      // First let's get the initial pickfirst set
      PromptSelectionResult sr =
        ed.SelectImplied();

      // Create a collection containing the initial set
      //  (could have used an array, but a collection is
      //  easier in dynamic situations, such as this)
      ObjectIdCollection objs;
      if (sr.Status == PromptStatus.OK)
        objs =
          new ObjectIdCollection(
          sr.Value.GetObjectIds()
        );
      else
        objs = new ObjectIdCollection();

      // Clear the pickfirst set...
      ed.SetImpliedSelection(new ObjectId[0]);
      // ...but highlight the objects
      if (objs.Count > 0)
        HighlightEntities(objs);

      // No ask the user to select objects
      sr = ed.GetSelection();
      if (sr.Status == PromptStatus.OK)
      {
        // Add them all to the collection
        foreach (ObjectId obj in sr.Value.GetObjectIds())
        {
          objs.Add(obj);
        }
        // Dump the collection to an array
        ObjectId[] ids = new ObjectId[objs.Count];
        objs.CopyTo(ids, 0);

        // And finally set the pickfirst set
        ed.SetImpliedSelection(ids);
      }
    }

    // Highlight the entities by opening them one by one
    private void HighlightEntities(ObjectIdCollection objIds)
    {
      Document doc =
        Application.DocumentManager.MdiActiveDocument;
      Transaction tr =
        doc.TransactionManager.StartTransaction();
      using (tr)
      {
        foreach (ObjectId objId in objIds)
        {
          Entity ent =
            tr.GetObject(objId, OpenMode.ForRead)
            as Entity;
          if (ent != null)
            ent.Highlight();
        }
      }
    }
  }
}