Exit from Inno Setup installation from [Code]

To prevent the installer from running, when prerequisites test fails, just return False from the InitializeSetup. This will exit the installer even before the wizard shows.

function InitializeSetup(): Boolean;
begin
  Result := True;

  if not PrerequisitesTest then
  begin                     
    SuppressibleMsgBox('Prerequisites test failed', mbError, MB_OK, IDOK);
    Result := False;
  end;
end;

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If you need to test prerequisites right before the installation starts only (i.e. the InitializeSetup is too early), you can call the Abort function from the CurStepChanged(ssInstall):

procedure CurStepChanged(CurStep: TSetupStep);
begin
  if CurStep = ssInstall then
  begin
    if not PrerequisitesTest then
    begin                     
      SuppressibleMsgBox('Prerequisites test failed', mbError, MB_OK, IDOK);
      Abort;
    end;
  end;
end;

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Though for this scenario, consider using the PrepareToInstall event function mechanism, instead of exiting the setup.

function PrepareToInstall(var NeedsRestart: Boolean): String;
begin
  Result := '';

  if not PrerequisitesTest then
  begin                     
    Result := 'Prerequisites test failed';
  end;
end;

---

If you need to force terminate the installer any other time, use the ExitProcess WinAPI call:

procedure ExitProcess(uExitCode: Integer);
  external '[email protected] stdcall';

function NextButtonClick(CurPageID: Integer): Boolean;
begin
  if CurPageID = wpReady then
  begin
    if not PrerequisitesTest then
    begin                     
      SuppressibleMsgBox('Prerequisites test failed', mbError, MB_OK, IDOK);
      ExitProcess(1);
    end;
  end;
  Result := True;
end;

Though this is rather unsafe exit, so use it only as the last resort approach. If you have any external DLL loaded, you might need to unload it first, to avoid crashes. This also does not cleanup the temporary directory.

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