{ unit uBaseInterfaces; }
…
  IMyInterface = interface(IInterface)
    procedure Init(ATxt:string);
  end;



{ unit uFormTest; }
…
type

  TFormTest = class(TForm, IMyInterface)
    lCpt: TLabel;
  public
    procedure Init(ATxt:string);
  end;

implementation

{$R *.dfm}

procedure TFormTest.Init(ATxt: string);
begin
  lCpt.Caption := ATxt;
  ShowModal;
end;

initialization
  RegisterClass(TFormTest);

end.



{ unit uMainForm; }
…
type

  TMainForm = class(TForm)
    btnInterfaceCall: TButton;
    procedure btnInterfaceCallClick(Sender: TObject);
  end;

implementation

uses uBaseInterfaces;

{$R *.dfm}

procedure TMainForm.btnInterfaceCallClick(Sender: TObject);
var vClass : TClass;
  vObj : TObject;
  vForm : TForm;
begin
  vClass := FindClass('TFormTest');
  vObj := vClass.Create;
  vForm := TForm(vObj).Create(nil);

  // Вызывает ошибку компиляции:
  // E2010 Incompatible types: 'IMyInterface' and 'TForm'
  //IMyInterface(vForm).Init('My message!');

  // Вызывает RunTimeError;
  //IMyInterface(@vForm).Init('My message!');
end;

 vObj : IMyInterface;

...
vObj := vClass.Create;
...

vObj := vClass.Create as IMyInterface 

var vClass : TClass;
  vI : IMyInterface;
begin
  vClass := FindClass('TFormTest');
  TFormClass(vClass).Create(Application).GetInterface(IMyInterface, vI);
  TFacade.ShowMsg(vI, 'My test message!');
end;