A Simple, Straight forward way of using 'IStrings' interface to
pass Multiple Strings from a COM Object.

The VCL Contains great amount of reusable code and Helper Objects implementing many standard COM interfaces. Particularly when in comes to the implementation of COM & related stuff, life has been made a lot easy.

One such demonstration of these beautiful helper objects is the Implementation of 'IStrings' interface via the 'TStringsAdapter' Class.

In this article we will take a sneak peak about how we can utilise this class effectively.

Assume this situation :

You are creating a loosely coupled, (COM based) business object.
you got to return a list of strings as result of a method call.
the options are many.

for ex. you may choose to return it as:
1. as a Variant Array.
2. as a huge string, seperated by delimeters
3. as an IStream
and more...

well, here is a much simpler option. most effective and faster to implement.

1. We create a TStringList object
2. fill it with strings
3. create a TStringsAdapter
4. pass the TStringList to the Adapter
5. retrieve an IStrings interface from the Adapter.

here is the code (COM Server) :

  {-- Interface Declaration --}

  IUsers = interface(IDispatch)
    ['{8195E30A-ADB7-459E-804A-32A97FE1A2DE}']
    function Get_UserRights(const AUserID: WideString): IStrings; safecall;
  end;

  {-- Interface Implementation --}

  TUsers = class(TAutoObject, IUsers)
  protected
    FUserRights : TStringList;
  public
    {Constructor, Destructor.... }

    function Get_UserRights(const AUserID: WideString): IStrings; safecall;
  end;

  function TUsers.Get_UserRights(const AUserID: WideString): IStrings;
  begin
    {--
      FUserRights : fill your TStringList with data here.
      FUserRights.Clear;
      FUserRights.Add('rt_view');
      FUserRights.Add('rt_add');
      FUserRights.Add('rt_update');
      FUserRights.Add('rt_delete');
      FUserRights.Add('rt_approve');
    --}
    Result := TStringsAdapter.Create( FUserRights ) as IStrings;
  end;

and at the Client Side,

1. Declare a variable of type IStrings
2. Create your COM Object
3. Call Get_UserRights and assign the result to the IStrings variable


procedure DisplayUserRights;
var
  oUsers : IUsers;
  oUserRights : IStrings;
  iCtr : integer;
begin
  oUsers := COUsers.Create;
  oUserRights := oUsers.Get_UserRights('');
  {-- Access the individual strings as oUserRights.Item[0]... --}
  {-- or you can copy it to a local TStringlist --}
  oUserRights := nil;
  oUsers := nil;
end;


{-- Dependencies, Deployment Considerations --}
You got to include 'StdVcl' unit in your uses clause and
stdvcl40.dll while deploying.
(stdvcl40.dll has to be registered.)

That's All Folks.
Hope it is useful.