BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  HOWTO: Implement an interface by delegation?          BorlandTalk.com Forum Index -> Delphi OLE Automation View previous topic :: View next topic   Author Message Ian Boyd Guest Posted: Fri Sep 08, 2006 10:32 pm    Post subject: HOWTO: Implement an interface by delegation? //i have a base object, and a newly created interface TShape = class(TObject) procedure Dummy; end; IBottle = interface(IDispatch) procedure Drink; safecall; end; {I want to create a descendant of TShape that implements IBottle i've actually created my own object that implements IDispatch for various good reasons and i want to delegate the handling of IDispatch to that child object:} TCustomDispatchThingy = class(TObject, IUnknown, IDispatch) public function QueryInterface(const IID: TGUID; out Obj): HResult; stdcall; function _AddRef: Integer; stdcall; function _Release: Integer; stdcall; function GetTypeInfoCount(out Count: Integer): HResult; stdcall; function GetTypeInfo(Index, LocaleID: Integer; out TypeInfo): HResult; stdcall; function GetIDsOfNames(const IID: TGUID; Names: Pointer; NameCount, LocaleID: Integer; DispIDs: Pointer): HResult; stdcall; function Invoke(DispID: Integer; const IID: TGUID; LocaleID: Integer; Flags: Word; var Params; VarResult, ExcepInfo, ArgErr: Pointer): HResult; stdcall; end; {Now i'm all set to create my descendant from the ancestor, and say that it implements the required interfaces:} TBottleShape = class(TShape, IUnknown, IDispatch, IBottle) private FDispatchHandler: TCustomDispatchThingy; public procedure Drink; safecall; property UnknownHandler: TCustomDispatchThingy read FDispatchHandler implements IUnknown; property DispatchHandler: TCustomDispatchThingy read FDispatchHandler implements IDispatch; end; But i get the errors here: Undeclared identifier: 'GetTypeInfoCount' Undeclared identifier: 'GetTypeInfo' Undeclared identifier: 'GetIDsOfNames' Undeclared identifier: 'Invoke' Undeclared identifier: 'QueryInterface' Undeclared identifier: '_AddRef' Undeclared identifier: '_Release' NOTES (1) TShape is locked, it cannot descend from anything else or change (2) IBottle is locked, it cannot descend from any other interface EXTRA QUESTION: If IBottle descends from IDispatch, why do i have to list IDispatch again? TBottleShape = class(TObject, IBottle, IDispatch) i realize that if i had done: TBottleShape = class(TAutoIntfObject, IBottle) i would not have to list IDispatch again, because it comes in with TAutoIntfObject. But why not the former syntax? What does it mean in Delphi for an interface to descend from another if that is never honored? What does it mean? What does it get me? Would IBottle1 = interface(IDispatch) be any different from IBottle2 = interface(IUnknown) Since in both cases i have to say: TBottle1 = class(TObject, IUnknown, IDispatch, IBottle1) TBottle2 = class(TObject, IUnknown, IBottle2) Is there such a thing in Delphi as interfaces descending from one another? Isn't IBottle = interface(IFooDummyGarbageName) and IBottle = interface identical? What does the former give me that the later doesn't? Back to top Marc Rohloff [TeamB] Guest Posted: Sat Sep 09, 2006 5:22 am    Post subject: Re: HOWTO: Implement an interface by delegation? On Fri, 8 Sep 2006 13:32:47 -0400, Ian Boyd wrote: Quote: But i get the errors here: Undeclared identifier: 'GetTypeInfoCount' .... Which class are you getting the errors on? Find the definition for IDispatch and IUnknown and make sure that the method specifications match. Quote: If IBottle descends from IDispatch, why do i have to list IDispatch again? TBottleShape = class(TObject, IBottle, IDispatch) This is just the way Delphi implements interfaces. You don't have to list IDispatch, but if you don't then you cannot typecast your interface to IDispatch. Quote: What does it mean in Delphi for an interface to descend from another if that is never honored? What does it mean? What does it get me? Would It would mean that anyone who has a reference using the IBottle interface can call all it's methods without doing a further typecast. In most cases this isn't what you want (They don't really care about GetTypeInfo, AddRef, etc) and I would use Quote: IBottle2 = interface ... Is there such a thing in Delphi as interfaces descending from one another? Yes Quote: Isn't IBottle = interface(IFooDummyGarbageName) and IBottle = interface identical? No Quote: What does the former give me that the later doesn't? All the methods in IFooDummyGarbageName without a further typecast. -- Marc Rohloff [TeamB] marc rohloff -at- myrealbox -dot- com Back to top Ian Boyd Guest Posted: Wed Sep 13, 2006 12:19 am    Post subject: Re: HOWTO: Implement an interface by delegation? Quote: It would mean that anyone who has a reference using the IBottle interface can call all it's methods without doing a further typecast. In most cases this isn't what you want (They don't really care about GetTypeInfo, AddRef, etc) and I would use So if i define some interfaces interface type IRohloff = interface public function GetRace: Integer; end; IMark = interface(IRohloff) public function GetFingerPrints: OleVariant; end; Then on the object TMarkRohloff = class(TInterfacedObject, IMark) i can call MarkRohloff.GetFingerPrints; and MarkRohloff.GetRace; But the MarkRohloff doesn't support IRohloff? i think this sounds like my problem... Consider: TMarkRohloff = class(TInterfacedObject, IMark, IRohloff) public function GetFingerPrints: OleVariant; function GetRace: Integer; end; There is now a duplicated method: IRohloff.GetRace and IMark.GetRace Does Delphi transparently make IMark.GetRace and IRohloff.GetRace use the same method? Back to top Marc Rohloff [TeamB] Guest Posted: Wed Sep 13, 2006 5:10 am    Post subject: Re: HOWTO: Implement an interface by delegation? On Tue, 12 Sep 2006 15:19:18 -0400, Ian Boyd wrote: Quote: But the MarkRohloff doesn't support IRohloff? No it doesn't, although you can access the IRohloff methods from an IMarc (Please note the important spelling here, An IMark interface will *never* work for you) Quote: There is now a duplicated method: IRohloff.GetRace and IMark.GetRace Does Delphi transparently make IMark.GetRace and IRohloff.GetRace use the same method? Yes -- Marc Rohloff [TeamB] marc rohloff -at- myrealbox -dot- com Back to top Ian Boyd Guest Posted: Wed Sep 13, 2006 11:34 pm    Post subject: Re: HOWTO: Implement an interface by delegation? Quote: Does Delphi transparently make IMark.GetRace and IRohloff.GetRace use the same method? Yes Soooooo damn tricky. Sooooo damn subtle. Soooooo little documentation. Sorry about the name typo Back to top Marc Rohloff [TeamB] Guest Posted: Thu Sep 14, 2006 7:31 am    Post subject: Re: HOWTO: Implement an interface by delegation? On Wed, 13 Sep 2006 14:34:06 -0400, Ian Boyd wrote: Quote: Soooooo damn tricky. Sooooo damn subtle. Soooooo little documentation. Yes, COM is largely a black art. I would recommend Delphi COM Programming by Eric Harmon (http://tinyurl.com/h5zt2) -- Marc Rohloff [TeamB] marc rohloff -at- myrealbox -dot- com Back to top Dennis Passmore Guest Posted: Thu Sep 14, 2006 5:12 pm    Post subject: Re: HOWTO: Implement an interface by delegation? Quote: Yes, COM is largely a black art. I would recommend Delphi COM Programming by Eric Harmon (http://tinyurl.com/h5zt2) Another good book was Delphi Developer's Guide to COM+ by Alexander Rodygin. It was a free download from http://www.softinterop.com/Home.aspx/dev/bookcomplus for a long time but I do not think it is online any more. I have the download "BookCOMPlus.zip" if someone needs it. Back to top Ian Boyd Guest Posted: Thu Sep 14, 2006 11:33 pm    Post subject: Re: HOWTO: Implement an interface by delegation? Quote: Yes, COM is largely a black art. I would recommend Delphi COM Programming by Eric Harmon (http://tinyurl.com/h5zt2) Have it, read it. Also have Don Box's book. Back to top Ian Boyd Guest Posted: Thu Sep 14, 2006 11:34 pm    Post subject: Re: HOWTO: Implement an interface by delegation? Quote: Another good book was Delphi Developer's Guide to COM+ by Alexander Rodygin. It was a free download from http://www.softinterop.com/Home.aspx/dev/bookcomplus for a long time but I do not think it is online any more. I have the download "BookCOMPlus.zip" if someone needs it. i don't need a book on COM+ for Delphi, i need a book on what COM+ is. 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