How to change MsgBox message caption at runtime?

Question

I need to change the default caption of a MsgBox message box at runtime. Currently it constantly shows the value of the SetupAppTitle directive as a caption:

[Setup]
SetupAppTitle=myAppName

But this is specified at compilation time. How to do this at runtime, e.g. from a [Code] section ?

Answer 1

I don't think changing of the application title (if possible) would be a good idea only for displaying dialog title. So I would use the Windows MessageBox which is even used by the MsgBox. Here is a simple example for Ansi/Unicode versions of Inno Setup:

[Code]
const
  MB_ICONERROR = $10;
  MB_ICONQUESTION = $20;
  MB_ICONWARNING = $30;
  MB_ICONINFORMATION = $40;

#ifdef UNICODE
  #define AW "W"
#else
  #define AW "A"
#endif

function MessageBox(hWnd: HWND; lpText, lpCaption: string;
  uType: UINT): Integer; external 'MessageBox{#AW}@user32.dll stdcall';

procedure ButtonOnClick(Sender: TObject);
begin
  MessageBox(0, 'Message Text', 'Message Caption', MB_OK or MB_ICONINFORMATION);
end;

Answer 2

This is how i finally did it:

[Code]
{ https://msdn.microsoft.com/en-us/library/windows/desktop/ms645505.aspx }
{ Use Windows MessageBox() function as an MsgBox() replacement. }
{ MessageBoxW is the UNICODE version of this API call. }
const
  { these are not exported in Inno Setup! }
  MB_ICONERROR = $00000010;
  MB_ICONWARNING = $00000030;
  MB_ICONINFORMATION = $00000040;
  MB_ICONQUESTION = $00000020;

function _MessageBoxW_(hWnd: Integer; lpText, lpCaption: String; uType: Cardinal): Integer;
  external '[e-mail] stdcall';

{ Usage: SysMsgBox('Error', 'Shit happens!', MB_OK or MB_ICONERROR); }
{        res =: SysMsgBox('Question', 'blah blah', MB_YESNO or  MB_ICONQUESTION); }
function SysMsgBox(const Caption, Message: String; const Flags: Integer): Integer;
begin
  Result :=
    _MessageBoxW_(StrToInt(ExpandConstant('{wizardhwnd}')), Message, Caption, Flags);
end;

Thanks to all for your help!