#BILTNA2018 Wish 3 Granted: Level remap to allow safe level deletion

The problem

If you delete a level in Revit, it deletes all objects on that level – no warning is given.

There should be a safe way of finding objects that are assigned to that level and reassigning them to a different level.

Perhaps Revit could automatically assign them to the level below?

Its a real problem if you create too many levels at the beginning of a project, you cant then delete some as you’ll lose information.

The solution – an API command to remap elements so they no longer reference the selected level

public void levelRemap()
{
    Document doc = this.ActiveUIDocument.Document;
    UIDocument uidoc = this.ActiveUIDocument;
    Level level = doc.GetElement(uidoc.Selection.PickObject(ObjectType.Element, "Select level")) as Level;
    
    Level levelBelow = new FilteredElementCollector(doc)
        .OfClass(typeof(Level))
        .Cast<Level>()
        .OrderBy(q => q.Elevation)
        .Where(q => q.Elevation <= level.Elevation)
        .FirstOrDefault();
    
    if (levelBelow == null)
    {
        TaskDialog.Show("Error", "No level below " + level.Elevation);
        return;
    }
    
    List<string> paramsToAdjust = new List<string> { "Base Offset", "Sill Height", "Top Offset"};
    
    List<Element> elements = new FilteredElementCollector(doc).WherePasses(new ElementLevelFilter(level.Id)).ToList();
    using (Transaction t = new Transaction(doc, "Level Remap"))
    {
        t.Start();
        foreach (Element e in elements)
        {
            foreach (Parameter p in e.Parameters)
            {
                if (p.StorageType != StorageType.ElementId || p.IsReadOnly)
                    continue;
                if (p.AsElementId() != level.Id)
                    continue;
                
                double elevationDiff = level.Elevation - levelBelow.Elevation;
                
                p.Set(levelBelow.Id);
                
                foreach (string paramName in paramsToAdjust)
                {
                    Parameter pToAdjust = e.LookupParameter(paramName);
                    if (pToAdjust != null && !pToAdjust.IsReadOnly)
                        pToAdjust.Set(pToAdjust.AsDouble() + elevationDiff);
                }
            }
        }
        t.Commit();
    }
}