El siguiente código (cuando está registrado en un paquete) nos da un componente llamadoTParentComponent registrado en el paletTest.

Sin embargo, cuando crea un objeto secundario utilizando el Editor de propiedades (proporcionado en el mismo código), el IDE muestra el mensaje de errorNo se puede crear un método para un componente sin nombre.

Lo que es extraño es que el objeto Niño sí tiene un nombre.

Aquí está la fuente:

unit TestEditorUnit;

interface

uses
  Classes, DesignEditors, DesignIntf;

type  
  TParentComponent = class;

  TChildComponent = class(TComponent)
  private
    FParent: TParentComponent;
    FOnTest: TNotifyEvent;
    procedure SetParent(const Value: TParentComponent);
  protected
    procedure SetParentComponent(AParent: TComponent); override;
  public
    destructor Destroy; override;
    function GetParentComponent: TComponent; override;
    function HasParent: Boolean; override;
    property Parent: TParentComponent read FParent write SetParent;
  published
    property OnTest: TNotifyEvent read FOnTest write FOnTest;
  end;

  TParentComponent = class(TComponent)
  private
    FChilds: TList;
  protected
    procedure GetChildren(Proc: TGetChildProc; Root: TComponent); override;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
  published
    property Childs: TList read FChilds;
  end;

  TParentPropertyEditor = class(TPropertyEditor)
  public
    function GetAttributes: TPropertyAttributes; override;
    function GetValue: string; override;
    procedure Edit; override;
  end;

procedure Register;

implementation

uses
  ColnEdit;

type
  TChildComponentCollectionItem = class(TCollectionItem)
  private
    FChildComponent: TChildComponent;
    function GetName: string;
    function GetOnTest: TNotifyEvent;
    procedure SetName(const Value: string);
    procedure SetOnTest(const Value: TNotifyEvent);
  protected
    property ChildComponent: TChildComponent read FChildComponent write FChildComponent;
    function GetDisplayName: string; override;
  public
    constructor Create(Collection: TCollection); override;
    destructor Destroy; override;
  published
    property Name: string read GetName write SetName;
    property OnTest: TNotifyEvent read GetOnTest write SetOnTest;
  end;

  TChildComponentCollection = class(TOwnedCollection)
  private
    FDesigner: IDesigner;
  public
    property Designer: IDesigner read FDesigner write FDesigner;
  end;

procedure Register;
begin
  RegisterClass(TChildComponent);
  RegisterNoIcon([TChildComponent]);
  RegisterComponents('Test', [TParentComponent]);
  RegisterPropertyEditor(TypeInfo(TList), TParentComponent, 'Childs', TParentPropertyEditor);
end;

{ TChildComponent }

destructor TChildComponent.Destroy;
begin
  Parent := nil;
  inherited;
end;

function TChildComponent.GetParentComponent: TComponent;
begin
  Result := FParent;
end;

function TChildComponent.HasParent: Boolean;
begin
  Result := Assigned(FParent);
end;

procedure TChildComponent.SetParent(const Value: TParentComponent);
begin
  if FParent <> Value then
  begin
    if Assigned(FParent) then
      FParent.FChilds.Remove(Self);
    FParent := Value;
    if Assigned(FParent) then
      FParent.FChilds.Add(Self);
  end;
end;

procedure TChildComponent.SetParentComponent(AParent: TComponent);
begin
  if AParent is TParentComponent then
    SetParent(AParent as TParentComponent);
end;

{ TParentComponent }

constructor TParentComponent.Create(AOwner: TComponent);
begin
  inherited;
  FChilds := TList.Create;
end;

destructor TParentComponent.Destroy;
var
  I: Integer;
begin
  for I := 0 to FChilds.Count - 1 do
    TComponent(FChilds[0]).Free;
  FChilds.Free;
  inherited;
end;

procedure TParentComponent.GetChildren(Proc: TGetChildProc; Root: TComponent);
var
  i: Integer;
begin
  for i := 0 to FChilds.Count - 1 do
    Proc(TComponent(FChilds[i]));
end;

{ TChildComponentCollectionItem }

constructor TChildComponentCollectionItem.Create(Collection: TCollection);
begin
  inherited;
  if Assigned(Collection) then
  begin
    FChildComponent := TChildComponent.Create(TComponent(TOwnedCollection(Collection).Owner).Owner);
    FChildComponent.Name := TChildComponentCollection(Collection).Designer.UniqueName(TChildComponent.ClassName);
    FChildComponent.Parent := TParentComponent(TComponent(TOwnedCollection(Collection).Owner));
  end;
end;

destructor TChildComponentCollectionItem.Destroy;
begin
  FChildComponent.Free;
  inherited;
end;

function TChildComponentCollectionItem.GetDisplayName: string;
begin
  Result := FChildComponent.Name;
end;

function TChildComponentCollectionItem.GetName: string;
begin
  Result := FChildComponent.Name;
end;

function TChildComponentCollectionItem.GetOnTest: TNotifyEvent;
begin
  Result := FChildComponent.OnTest;
end;

procedure TChildComponentCollectionItem.SetName(const Value: string);
begin
  FChildComponent.Name := Value;
end;

procedure TChildComponentCollectionItem.SetOnTest(const Value: TNotifyEvent);
begin
  FChildComponent.OnTest := Value;
end;

{ TParentPropertyEditor }

procedure TParentPropertyEditor.Edit;
var
  LCollection: TChildComponentCollection;
  i: Integer;
begin
  LCollection := TChildComponentCollection.Create(GetComponent(0), TChildComponentCollectionItem);
  LCollection.Designer := Designer;
  for i := 0 to TParentComponent(GetComponent(0)).Childs.Count - 1 do
    with TChildComponentCollectionItem.Create(nil) do
    begin
      ChildComponent := TChildComponent(TParentComponent(GetComponent(0)).Childs[i]);
      Collection := LCollection;
    end;
  ShowCollectionEditorClass(Designer, TCollectionEditor, TComponent(GetComponent(0)), LCollection, 'Childs');
end;

function TParentPropertyEditor.GetAttributes: TPropertyAttributes;
begin
  Result := [paDialog];
end;

function TParentPropertyEditor.GetValue: string;
begin
  Result := 'Childs';
end;

end.

La fuente anterior fue adaptada deOtra respuesta aquí en StackOverflow.

Cualquier idea de por qué no puedo crear un método paraOnTest?

¡Gracias por adelantado!