RTTI access to private methods of VCL, e.g. TCustomForm.SetWindowState

Question

In the debate about the closing of the class helper loophole that allowed easy access to private members (fields and methods) of a class in Delphi 10.1 Berlin, it is often claimed that

extended RTTI allows access to the private members of a class that was compiled with (extended) RTTI enabled, and
all VCL/RTL/FMX classes have this enabled.

However, if I run this simple unit (a simple form with one TListBox, nothing else):

unit RttiAccessTest;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, System.Rtti, Vcl.StdCtrls;

type
  TForm16 = class(TForm)
    ListBox1: TListBox;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form16: TForm16;

implementation

{$R *.dfm}

function GetMethodString(const MethodName: string): string;
var
  M: TRTTIMethod;
  I: Integer;
begin
  M := TRttiContext.Create.GetType(TCustomForm).GetMethod(MethodName);
  if Assigned(M) then
    Result := 'Method ' + MethodName + ': ''' + M.ToString + ';'''
  else
    Result := 'Method ' + MethodName + ' cannot be found';
end;

procedure TForm16.FormCreate(Sender: TObject);
begin
  Listbox1.Items.Add(GetMethodString('SetWindowState'));
  Listbox1.Items.Add(GetMethodString('ShowModal'));
end;

end.

The text in the list box is:

Method SetWindowState cannot be found 
Method ShowModal: 'function ShowModal: Integer;'

This means I cannot get access to this private method SetWindowState of TCustomForm. Is this because not all classes in the RTL/VCL/FMX have extended RTTI, or am I doing something wrong?

If I am doing something wrong or forgetting something, then what? In other words, what do I have to do to get RTTI access to, say, SetWindowState of TCustomForm? I cannot get this access in Seattle or earlier either.

Note

I know how to get access to the method anyway, using the fact that class helpers can still get the address of private methods, but that is not my question. I am particularly asking about how to do this with RTTI.

There was an identical question a couple of days ago, searching... — LU RD
Found it: How to access the private method TStreamReader.FillBuffer in Delphi 10.1 Berlin?. Conclusion was that {$MethodInfo} is OFF by default in the RTL. — LU RD
But there, the answer mentioned the class helper addres/method trick. Not how to od it with RTTI. Obviously, it is not possible with RTTI. — Rudy Velthuis

David Heffernan David Heffernan · Accepted Answer · 2016-06-19T08:42:01

The obvious conclusion is that whilst this type is compiled with extended RTTI, that RTTI is not included for private methods.

RTTI access to private methods of VCL, e.g. TCustomForm.SetWindowState

Note

2 Answers