How to determine the version number of a registered OCX in Delphi XE2

Question

I have an ActiveX component in XE2 that connects to a database to handle transaction processing, and it includes a check of its version against that of the database to determine if they are compatible.

Unlike C#, where the AssemblyVersion attribute can be obtained at runtime using the Application.ProductVersion property, Delphi XE2 has no such built-in property for getting the version information included in the project options, with the preferred method being to use GetFileVersionInfo, passing in the full path to the program, or in this case the OCX.

Originally the OCX was always installed to the Windows System path but we have changed our installation process so that the OCX is installed to the same folder as the executable that uses it, which is a location determined by the user.

What I need is a consistent method that I can use from within the OCX code to obtain the installation folder from the registry across the multitude of Windows environments. I assume it would have something to do with the GUID's defined in the _TLB.pas file.

Answer 1

You don't need to query the Registry at all. The OCX can retreive its own filename by passing Delphi's global HInstance variable as the module handle to the Win32 API GetModuleFileName() function, then it can pass that filename to GetFileVersionInfo() .

Although, a better way for the OCX to access its own version, without resorting to GetFileVersionInfo() , is to use Find/Load/LockResource() to access its own version resource directly, then no filename is needed at all. You can copy the version resource data into a temp buffer and pass that to VerQueryValue() to retrieve the resource's VS_FIXEDFILEINFO structure (retrieving anything else from the resource gets a bit trickier because GetFileVersionInfo() prepares certain lookup data that VerQueryValue() then uses).

Answer 2

You certainly don't need to use the registry here. Not least because there could potentially be multiple versions of the DLL on the machine, because you are installing to the executable directory of any program that uses the DLL.

You could certainly read the version resource as Remy describes. But another alternative would be to include a constant in your program that encodes the database version compatibility.

const
  DatabaseVersion = 1;

Check this constant against the value read from the database and fail if not compatible.

To me this makes a little more sense as it separates the version of the DLL from the version of the database. The two are not necessarily linked. You could, and probably do, update the DLL without changing the database structure.