Registering DLL and ActiveX controls from code

http://delphi.about.com/od/windowsshellapi/l/aa040803a.htm

How to register (and unregister) OLE controls such as dynamic-link library (DLL) or ActiveX Controls (OCX) files from a Delphi application.

One of the features that make Delphi so popular is that when it comes to project deployment, you as a developer (in most cases) only need to send the executable file (exe) of your application.

However, in some situations, for example when you import an ActiveX control into your project, you'll need to make sure that this ActiveX control is registered on your users machines. If the control is not registered there, an EOleSysError exception will be displayed to your user eyes.

RegSvr32.exe
The regsvr32.exe command-line tool registers dll and ActiveX controls on a system. You can manually use the Regsvr32.exe (Windows.Start - Run) to register and unregister OLE controls such as dynamic link library (DLL) or ActiveX Controls (OCX) files that are self-registerable. 
When you use Regsvr32.exe, it attempts to load the component and call its DLLSelfRegister function. If this attempt is successful, Regsvr32.exe displays a dialog indicating success.

RegSvr32.exe has the following command-line options:

Regsvr32 [/u] [/s] [/n] [/i[:cmdline]] dllname
 /s - Silent; display no message boxes
 /u - Unregister server
 /i - Call DllInstall passing it an optional [cmdline]; when used with /u calls dll uninstall
 /n - do not call DllRegisterServer; this option must  be used with /i

From Delphi code

To call the regsvr32 tool from within Delphi code, you'll need a function that can execute a file and wait for the execution to finish.

This is how the 'RegisterOCX' procedure could look:

procedure RegisterOCX;
type
  TRegFunc = function : HResult; stdcall;
var
  ARegFunc : TRegFunc;
  aHandle  : THandle;
  ocxPath  : string;
begin
 try
  ocxPath := ExtractFilePath(Application.ExeName) + 'Flash.ocx';
  aHandle := LoadLibrary(PChar(ocxPath));
  if aHandle <>  then
  begin
    ARegFunc := GetProcAddress(aHandle,'DllRegisterServer');
    if Assigned(ARegFunc) then
    begin
      ExecAndWait('regsvr32','/s ' + ocxPath);
    end;
    FreeLibrary(aHandle);
  end;
 except
  ShowMessage(Format('Unable to register %s', [ocxPath]));
 end;
end;

Note: the ocxPath variable points to the 'Flash.ocx' Macromedia ActiveX control.

To be able to register itself, an ActiveX control needs to implement the DllRegisterServer function. In simple words, this function creates registry entries for all the classes inside the control. We do not need to worry about the DllRegisterServer function we just want to make sure it is there. For the sake of simplicity, we've presumed that the ActiveX control (the *.ocx file) is located in the same folder as where your application is.

The red line in the above code, does the job of calling the regsvr32 tool by passing the "/s" switch along with the full path to the ActiveX control. The function is ExecAndWait.

uses shellapi;
...
function ExecAndWait(const ExecuteFile, ParamString : string): boolean;
var
  SEInfo: TShellExecuteInfo;
  ExitCode: DWORD;
begin
  FillChar(SEInfo, SizeOf(SEInfo), );
  SEInfo.cbSize := SizeOf(TShellExecuteInfo);
  with SEInfo do begin
    fMask := SEE_MASK_NOCLOSEPROCESS;
    Wnd := Application.Handle;
    lpFile := PChar(ExecuteFile);
    lpParameters := PChar(ParamString);
    nShow := SW_HIDE;
  end;
  if ShellExecuteEx(@SEInfo) then
  begin
    repeat
      Application.ProcessMessages;
      GetExitCodeProcess(SEInfo.hProcess, ExitCode);
    until (ExitCode <> STILL_ACTIVE) or Application.Terminated;
    Result:=True;
  end
  else Result:=False;
end;

The above, ExecAndWait, function uses ShellExecuteEx API call to execute a file on a system. If you need more examples of executing any file from Delphi, check the Start from Delphiarticle.