Inno Setup - How to edit the “About Setup” dialog text box

Question

I need to edit or replace the text in the About Setup dialog box text of Inno Setup.

Here is a picture:

Answer 1

You need to give the saved original windows procedure back to the wizard form before you exit the setup application. To do so, use something like this:

const
  GWL_WNDPROC = -4;

procedure DeinitializeSetup;
begin
  SetWindowLong(WizardForm.Handle, GWL_WNDPROC, OldProc);
end;

Anyway, you can use more trustful library for wrapping callbacks, the InnoCallback library. I've made a review of the code you used and added support for Unicode InnoSetup versions, expecting the use of the InnoCallback library:

[Files]
Source: "InnoCallback.dll"; DestDir: "{tmp}"; Flags: dontcopy

[Code]
#ifdef UNICODE
  #define AW "W"
#else
  #define AW "A"
#endif
const
  GWL_WNDPROC = -4;
  SC_ABOUTBOX = 9999;
  WM_SYSCOMMAND = $0112;

type
  WPARAM = UINT_PTR;
  LPARAM = LongInt;
  LRESULT = LongInt;
  TWindowProc = function(hwnd: HWND; uMsg: UINT; wParam: WPARAM; 
    lParam: LPARAM): LRESULT;

function CallWindowProc(lpPrevWndFunc: LongInt; hWnd: HWND; Msg: UINT; 
  wParam: WPARAM; lParam: LPARAM): LRESULT;
  external 'CallWindowProc{#AW}@user32.dll stdcall';  
function SetWindowLong(hWnd: HWND; nIndex: Integer; 
  dwNewLong: LongInt): LongInt;
  external 'SetWindowLong{#AW}@user32.dll stdcall';    
function WrapWindowProc(Callback: TWindowProc; ParamCount: Integer): LongWord;
  external 'wrapcallback@files:InnoCallback.dll stdcall'; 

var
  OldWndProc: LongInt;

procedure ShowAboutBox;
begin
  MsgBox('Hello, I''m your about box!', mbInformation, MB_OK);
end;

function WndProc(hwnd: HWND; uMsg: UINT; wParam: WPARAM; 
  lParam: LPARAM): LRESULT;
begin
  if (uMsg = WM_SYSCOMMAND) and (wParam = SC_ABOUTBOX) then
  begin
    Result := 0;
    ShowAboutBox;
  end
  else
    Result := CallWindowProc(OldWndProc, hwnd, uMsg, wParam, lParam);
end;

procedure InitializeWizard;
begin
  OldWndProc := SetWindowLong(WizardForm.Handle, GWL_WNDPROC, 
    WrapWindowProc(@WndProc, 4));
end;

procedure DeinitializeSetup;
begin
  SetWindowLong(WizardForm.Handle, GWL_WNDPROC, OldWndProc);
end;