which is the best way to control a object-field type life-cycle?

Question

TMyClass = class(TObject)
private
  FMyObject: TObject;
  function GetMyObject: TObject;
public
  property MyObject: TObject read GetMyObject write FMyObject;
end;

function TMyClass.GetMyObject: TObject;
begin
  if FMyObject = nil then
    FMyObject := TObject.Create;

  Result := FMyObject;
end;

Sometimes, "MyObject" is not created internally but externally created and assigned to the parameter. If this object is created externally, I can not free it in this context.

Should I create a TList and Add in all objects that were created internally and destroy everything on the destructor?

How can I control the lifetime of a parameter if it is created internally or not? What you suggest to do? Is there any pattern to do this?

Answer 1

I'd set a flag in the Property Setter

procedure TMyClass.SetMyObject(AObject: TObject);
begin
  if Assigned(MyObject) and FIsMyObject then
    FMyObject.Free;
  FIsMyObject := False;
  FMyObject := AObject;
end;

function TMyClass.GetMyObject: TObject;
begin
  if FMyObject = nil then
  begin
    FMyObject := TObject.Create;
    FIsMyObject := True;
  end;

  Result := FMyObject;
end;

Destructor TMyClass.Destroy;
begin
    if FIsMyObject then
        FMyObject.Free;
end;