InstallShield 安装程序判断用户是否已安装Microsoft SQL Server或MS

这个例子是判断用户是否已安装Microsoft SQL Server或MSDE！如果没有安装则给出提示，提示用户必须要先安装并退出安装程序！

//---------------------------------------------------------------------------
// OnBegin
//
// The OnBegin event is called directly by the framework after the setup
// initializes.
//---------------------------------------------------------------------------
function OnBegin()
STRING szMsg;
STRING  sKey, sValue, sData;
    NUMBER  nType, nSize;
    NUMBER  nResult;
begin
// TO DO: you may change default non-UI setting, for example
//
// You may also perform your custom initialization steps, check requirements, etc.
if !MAINTENANCE then
   // 判断系统是否安装Microsoft SQL Server或MSDE
  sKey = "Software\\Microsoft\\Microsoft SQL Server"; 
     sValue = "InstalledInstances";
     szMsg = "Micorsoft SQL Server or MSDE was not found on this machine. This installation was designed to run only on the server machine.";
  RegDBSetDefaultRoot(HKEY_LOCAL_MACHINE);
  nResult = RegDBGetKeyValueEx ( sKey, sValue, nType, sData, nSize );
  if ( nResult < 0 )then
   // SQL Server registry key is missing
   SetDialogTitle ( DLG_MSG_INFORMATION, "Information" );
      MessageBox (szMsg,INFORMATION);
   abort;
  endif;
endif;
end;