How can I get the sub-item type of a TObjectList purely by RTTI information (i.e. without using any actual object instance) in Delphi?

Question

I\'m implementing generic code for streaming arbitrary Delphi objects using RTTI, and in order to get this to work (more specifically, in order to get the loading part to wo

Answer 1

I've been looking for a solution about this and I had an ideia that I'd like to share with you. That solution uses rtti and get the method's argument "Add" from a list(TList,TObjectList,etc). In my function I just return the Class Type, but you can easyly implements to primivite types. I hope it can help someone. Regards.

Folow:

class function TUtilRtti.GetSubTypeItemClassFromList(ObjectList: TObject): TClass;
var
  ctxRtti  : TRttiContext;
  typeRtti : TRttiType;
  atrbRtti : TCustomAttribute;
  methodRtti: TRttiMethod;
  parameterRtti: TRttiParameter;
begin
  result := nil;

  ctxRtti  := TRttiContext.Create;
  typeRtti := ctxRtti.GetType( ObjectList.ClassType );
  methodRtti := typeRtti.GetMethod('Add');
  for parameterRtti in methodRtti.GetParameters do
  begin
    if SameText(parameterRtti.Name,'Value') then
    begin
      if parameterRtti.ParamType.IsInstance then
        result := parameterRtti.ParamType.AsInstance.MetaclassType;
      break;
    end;
  end;
  ctxRtti.Free;
end;

Sample

...
var
  List: TList;
begin
  List := TList.Create();

  ShowMessage(TUtilRtti.GetSubTypeItemClassFromList(List).ClassName);
end;