Associate an application with a file extension

The code in the OnClick for Button1 sets "adp" to be opened by "c:\myadpapp.exe". ~~~~~~~~~~~~~~~~~~~~~~~~~
uses registry, shlobj;

procedure RegisterFileType(ExtName:String; AppName:String) ;
var
     reg:TRegistry;
begin
     reg := TRegistry.Create;
     try
          reg.RootKey:=HKEY_CLASSES_ROOT;
          reg.OpenKey('.' + ExtName, True) ;
          reg.WriteString('', ExtName + 'file') ;
          reg.CloseKey;
          reg.CreateKey(ExtName + 'file') ;
          reg.OpenKey(ExtName + 'file\DefaultIcon', True) ;
          reg.WriteString('', AppName + ',0') ;
          reg.CloseKey;
          reg.OpenKey(ExtName + 'file\shell\open\command', True) ;
          reg.WriteString('',AppName+' "%1"') ;
          reg.CloseKey;
     finally
          reg.Free;
     end

     SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, nil, nil) ;
end;


procedure TForm1.Button1Click(Sender: TObject) ;
begin
     RegisterFileType('adp','c:\myadpapp.exe') ;
end;
~~~~~~~~~~~~~~~~~~~~~~~~~