dual interface
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Thanks CPallini, I have did more study and I want to share my points here. Could you help to review whether my points are correct please? :-) 1. If a component implements IDispatch directly, we can only invoke its member methods through IDispatch.Invoke -- only one way, so it is not dual interface; 2. If a component implements IUnknown directly, we can only use AddRef/Release/QueryInterface, it is useless since we can only use the 3 methods; 3. If a component implements a customized interface, then the customized interface implements IUnknown, then we could invoke the component's member methods through QueryInterface to get the customized interface, and using the vtable in the customized interface to invoke member methods. But still one way, so it is not dual interface; 4. If a component implements a customized interface, then the customized interface implements IDispatch, then we could invoke the component's member methods through QueryInterface to get the customized interface, and using the vtable in the customized interface to invoke member methods, and also we could invoke through IDispatch.Invoke. Two ways to invoke it, so called dual interface. All of my understandings are correct? Anything missing? :-) regards, George
IMHO your understandings are correct. Point (2), as it stands, IMHO is misleading: since
IUnknownimplementation is mandatory, I will say: if a component implements onlyIDispatch... But such a point is obvious. Also, as you know well,IDispatch, like any otherCOMinterface must provideIUnknown, then saying: "implementing only IDispatch" it is equivalent to say: "implementing aIUnknownwhoseQueryInterfacemethod may return onlyIDispatch". :)If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles] -
George_George wrote:
1. I am still confused. Dual interface means two ways to invoke methods of my class. One of them is through IDispatch.Invoke, the other way is?
Via another interface's
VTABLE.George_George wrote:
2. Confused about what do you mean -- "Implement the vtable part of the interface in your class."
Suppose you have (only) a method (say
Add) you can use viaIDispatch::Invoke. Implement theVTABLEpart of the interface means: provide an interface, sayIOperationexposing theAddmethod (since such method is not directly exposed byIDispatch). Possibly the final COM component interface inherits both fromIDispatchandIOperation, as Sandip I don't remember the technical details and, as usual: "this in going on my arrogant assumptions..." :)If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]Hi CPallini, I am not sure that we require an extra Interface. Check this Link Dual Interfaces[^] I could not find some good sample for this do you have one which will explain step by step procedure.. I am asking for this because i have never implemented this ..
CPallini wrote:
Sandip I don't remember the technical details and, as usual: "this in going on my arrogant assumptions..." Smile
:laugh:
Regards, Sandip.
modified on Friday, September 12, 2008 4:31 AM
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Hi CPallini, I am not sure that we require an extra Interface. Check this Link Dual Interfaces[^] I could not find some good sample for this do you have one which will explain step by step procedure.. I am asking for this because i have never implemented this ..
CPallini wrote:
Sandip I don't remember the technical details and, as usual: "this in going on my arrogant assumptions..." Smile
:laugh:
Regards, Sandip.
modified on Friday, September 12, 2008 4:31 AM
I think you're right, since you may simply do something like:
class IMyDualInterface : public IDispatch
with a VTABLE arranged the following way:
- QueryInterface methods
- IDispatch methods
- 'Add' method here.
:)
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles] -
Thanks CPallini, I have did more study and I want to share my points here. Could you help to review whether my points are correct please? :-) 1. If a component implements IDispatch directly, we can only invoke its member methods through IDispatch.Invoke -- only one way, so it is not dual interface; 2. If a component implements IUnknown directly, we can only use AddRef/Release/QueryInterface, it is useless since we can only use the 3 methods; 3. If a component implements a customized interface, then the customized interface implements IUnknown, then we could invoke the component's member methods through QueryInterface to get the customized interface, and using the vtable in the customized interface to invoke member methods. But still one way, so it is not dual interface; 4. If a component implements a customized interface, then the customized interface implements IDispatch, then we could invoke the component's member methods through QueryInterface to get the customized interface, and using the vtable in the customized interface to invoke member methods, and also we could invoke through IDispatch.Invoke. Two ways to invoke it, so called dual interface. All of my understandings are correct? Anything missing? :-) regards, George
When you say a component implements IDispatch or IUnknown im assuming that you have an interface IX that is derived from either of those interfaces (IDispatch or IUnknown)and you are implementing those intrefaces in a coclass. 1. Any COM interface has to be derived from IUnknown. So when you implement IDispatch you also have to implement IUnknown, because IDispatch is also derived from IUnknown. Any interface,say IX, that is derived from IDispatch is a dual interface. Because IX methods can be invoked through IDispatch methods as well as vtable. 2. You can also derive your interface IX from IUnknown and invoke its methods through vtable. 3,4. Don't know what you mean by customized interface. May i suggest that you go through "Inside COM" by Dale Rogerson. It is a very good book it will help you in understanding COM much better.
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Hi CPallini, I am not sure that we require an extra Interface. Check this Link Dual Interfaces[^] I could not find some good sample for this do you have one which will explain step by step procedure.. I am asking for this because i have never implemented this ..
CPallini wrote:
Sandip I don't remember the technical details and, as usual: "this in going on my arrogant assumptions..." Smile
:laugh:
Regards, Sandip.
modified on Friday, September 12, 2008 4:31 AM
Thanks Sandip, I am a little losting the context you are talking about. Do you mean in order to implement a dual interface, - we need an additional customized interface, which implements IDispatch? - or we need implement both an additional customized interface (and the customized interface inherits from IUnknown) and also implement IDispatch? - or both the above two ways are fine? regards, George
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I think you're right, since you may simply do something like:
class IMyDualInterface : public IDispatch
with a VTABLE arranged the following way:
- QueryInterface methods
- IDispatch methods
- 'Add' method here.
:)
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]Thanks CPallini, I am a little losing the context and my English is not very good. Do you guys mean in order to implement a dual interface, - we need an additional customized interface, which implements IDispatch? - or we need implement both an additional customized interface (and the customized interface inherits from IUnknown) and also implement IDispatch? - or both the above two ways are fine? regards, George
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IMHO your understandings are correct. Point (2), as it stands, IMHO is misleading: since
IUnknownimplementation is mandatory, I will say: if a component implements onlyIDispatch... But such a point is obvious. Also, as you know well,IDispatch, like any otherCOMinterface must provideIUnknown, then saying: "implementing only IDispatch" it is equivalent to say: "implementing aIUnknownwhoseQueryInterfacemethod may return onlyIDispatch". :)If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]Thanks CPallini! http://www.codeproject.com/script/Forums/View.aspx?fid=1647&msg=2720744[^] Your reply is very clear. I post my further question here. Do you have any ideas? :-) regards, George
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Thanks CPallini, I am a little losing the context and my English is not very good. Do you guys mean in order to implement a dual interface, - we need an additional customized interface, which implements IDispatch? - or we need implement both an additional customized interface (and the customized interface inherits from IUnknown) and also implement IDispatch? - or both the above two ways are fine? regards, George
We need a customized interface that implements (also)
IDispatch(Usually it inherits fromIDispatch, that in turn, inherits fromIUnknown). :)If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles] -
When you say a component implements IDispatch or IUnknown im assuming that you have an interface IX that is derived from either of those interfaces (IDispatch or IUnknown)and you are implementing those intrefaces in a coclass. 1. Any COM interface has to be derived from IUnknown. So when you implement IDispatch you also have to implement IUnknown, because IDispatch is also derived from IUnknown. Any interface,say IX, that is derived from IDispatch is a dual interface. Because IX methods can be invoked through IDispatch methods as well as vtable. 2. You can also derive your interface IX from IUnknown and invoke its methods through vtable. 3,4. Don't know what you mean by customized interface. May i suggest that you go through "Inside COM" by Dale Rogerson. It is a very good book it will help you in understanding COM much better.
Thanks sw@thi, 1. You mentioned twice about "invoke its methods through vtable". My confusion is what exactly mean "through vtable". I think you mean QueryInterface for interface IX for the coclass object, and invoke the exposed methods in IX is through vtable of coclass object for interface IX. Correct? 2.
sw@thi wrote:
3,4. Don't know what you mean by customized interface.
Customized interface I mean any C++ eligible interface which is not IDispatch and IUnknown, and in 3 the customized interface inherits IUnknown and in 4 the customized interface inherits IDispatch. From my description, do you think my points for 3 and 4 are both correct? regards, George
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We need a customized interface that implements (also)
IDispatch(Usually it inherits fromIDispatch, that in turn, inherits fromIUnknown). :)If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles] -
We need a customized interface that implements (also)
IDispatch(Usually it inherits fromIDispatch, that in turn, inherits fromIUnknown). :)If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]Thanks CPallini, I have one more comment, at first I agree with what you mean above. I think there is another way to implement dual interface, which is we need implement both an additional customized interface (and the customized interface inherits from IUnknown) and also implement IDispatch (in IDispatch's Invoke implementation we can call the methods from the customized interface methods' implementation)? Is that also dual interface? regards, George
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Hi CPallini, I didn't find any simple article or example to do this on CP, which will explain steps. Do you know any? If not i think George can write one side by side as he implements Dual Interface :)
Regards, Sandip.
I am also asking for this, about various ways to implement dual interface. regards, George
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Hi CPallini, I didn't find any simple article or example to do this on CP, which will explain steps. Do you know any? If not i think George can write one side by side as he implements Dual Interface :)
Regards, Sandip.
SandipG wrote:
Do you know any?
Unfortunately, no. :sigh:
SandipG wrote:
If not i think George can write one side by side as he implements Dual Interface
Oh, he's writing the George's COM Bible! :-D
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]modified on Friday, September 12, 2008 5:39 AM
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Thanks CPallini, I have one more comment, at first I agree with what you mean above. I think there is another way to implement dual interface, which is we need implement both an additional customized interface (and the customized interface inherits from IUnknown) and also implement IDispatch (in IDispatch's Invoke implementation we can call the methods from the customized interface methods' implementation)? Is that also dual interface? regards, George
I think the standard way is just inheriting from
IDispatch(sinceIDispatchin turn inherits fromIUnknown) this way does not preventIDispatch::Invoketo call the methods of the customized interface. :)If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles] -
I think the standard way is just inheriting from
IDispatch(sinceIDispatchin turn inherits fromIUnknown) this way does not preventIDispatch::Invoketo call the methods of the customized interface. :)If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]I agree, but my implementation above is wrong and not dual interface, CPallini? regards, George
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I think the standard way is just inheriting from
IDispatch(sinceIDispatchin turn inherits fromIUnknown) this way does not preventIDispatch::Invoketo call the methods of the customized interface. :)If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]Just think of one more point to clarify -- we always mentioned of the dual interface access methods is -- invoke its methods through vtable. My confusion is what exactly mean "through vtable". I think it means using QueryInterface for customized interface for the coclass object, and invoke the exposed methods in the customized interface is through vtable of coclass object for the customized interface. Correct? regards, George
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I agree, but my implementation above is wrong and not dual interface, CPallini? regards, George
Well, it depends on how do you implement the
IDispatchinterface (for instance, if your customized interface inherits both fromIUnknownandIDispatchthe you've a undesirable diamond inehritance path). :)If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles] -
Just think of one more point to clarify -- we always mentioned of the dual interface access methods is -- invoke its methods through vtable. My confusion is what exactly mean "through vtable". I think it means using QueryInterface for customized interface for the coclass object, and invoke the exposed methods in the customized interface is through vtable of coclass object for the customized interface. Correct? regards, George
Yes, it means (1) get the
IUnknownpointer (2) get theICustomizedpointer viaIUnknown->QueryInterface(3) callICustomized->WhateverMethod()(eventually perform cleanup...) on the other hand, access viaIDispatchis quite different. :)If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles] -
Hi George, Read this link about implementing Dual interfaces. I think things shoudl be clear after this. Dual Interface[^]
George_George wrote:
My confusion is dual means (IDispatch/IUnknown) or (IDispatch/customized interface)?
I think dual interface does not mean two interfaces its about the ways you can access methods. I hope it helps..
Regards, Sandip.
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Dual interface refers to supporting both IDispatch and a VTBL, which means you can call it through COM using QueryInterface or from C++ directly. Been so long since I've done it, I'm a bit fuzzy on the details.
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