Get UIDocument

UIDocument uidoc = commandData.Application.ActiveUIDocument;

Get Element

Reference r = uidoc.Selection.PickObject(Autodesk.Revit.UI.Selection.ObjectType.Element);
try
            {
                if (r != null)
                {
                    TaskDialog.Show("Element ID", r.ElementId.ToString());
                }

                return Result.Succeeded;
            }
            catch (Exception ex)
            {
                message = ex.Message;
                return Result.Failed;
            }

#Register Addin Revit

Add file Application Manifest File, note (xxx.addin)

<?xml version="1.0" encoding="utf-8"?>
<RevitAddIns>

    <Assembly>MyFristCommand.dll</Assembly>
      <ClientId>xxx</ClientId>
      <FullClassName>MyFirstCommand.MyElement</FullClassName>
      <Text>GetElemenyId</Text>
      <VisibilityMode>AlwaysVisible</VisibilityMode>
      <AddInId>50930344-E64B-4AF6-9AD8-3D23311D4B56</AddInId>
      <LanguageType>Unknown</LanguageType>
      <VendorId>TeeMee</VendorId>
      <VendorDescription>FelixTran, www.teemee.com</VendorDescription>

</RevitAddIns>

Get GUIDs from https://www.guidgen.com/ and paste to AddInId

How To Build Project

Build project to file .dll

copy "$(TargetPath)" "%ProgramData%/Autodesk\Revit\Addins\2021\"
copy "$(ProjectDir)DeleteDoors.addin" "%ProgramData%/Autodesk\Revit\Addins\2021\"

How to Debug Project

Get Element Form ElementID

Get ElementType

FilteredElementCollector

Create Collection

FilteredElementCollector collection = new FilteredElementCollector(doc);

Create Filter

ElementCategoryFilter filterDoor = new ElementCategoryFilter(BuiltInCategory.OST_Doors);

Apply Filter to collection

IList<Element> doors =  collection.WherePasses(filterDoor).WhereElementIsNotElementType().ToElements();

Transaction

using (Transaction trans = new Transaction(doc, "change element"))
                    {
                        trans.Start();
                        doc.Delete(r.ElementId);
                        TaskDialog tDialog = new TaskDialog("Delete Element");
                        tDialog.MainContent = "Are you sure delete object?";
                        tDialog.CommonButtons = TaskDialogCommonButtons.Ok | TaskDialogCommonButtons.Cancel;
                        if (tDialog.Show() == TaskDialogResult.Ok)
                        {
                            trans.Commit();
                            TaskDialog.Show("Delete Element", " Yu delete this object" + r.ElementId.ToString())
                        }
                        else
                        {
                            trans.Commit();
                            TaskDialog.Show("Delete Element",  "Phan tu" +r.ElementId.ToString()+"chua bi xoa")

                        }
                    }

Family