In lesson 2, you learned that dispatch interfaces implement microsofts automation technology. It provides the basic ability to cast a instance of a com object to any of its supported interfaces queryinterface. Even if you late bind through an idispatch interface, you still need to know. The implementation adds a single idispatch implementation to the class, and uses typeinfo to dispatch against the pure interfaces.
This interface, and the marshaling code built for it, are now known as the automation facility. Extending iunknown, it is one of the standard interfaces that can be exposed by com objects. By george shepherd and scot wingo, december 01, 1997. Idispatch interface from the expert community at experts exchange. But if you want to do that you can use queryinterface to get idispatch pointer but that. All other com interfaces are inherited, directly or indirectly, from iunknown. In fact, the genius of idispatch is that it was defined using just four methodsgettypeinfocount, gettypeinfo, getidsofnames, and invoke. The idispatch interface would have to contain an infinite number of methods. If an interface a is derived only from iunknown we have. In addition to the methods inherited from iunknown, server developers must implement the following methods within the class definition of each object that is exposed. The idispatch interface exposes a number of methods for automation clients that require latebinding such as scripting languages. At over 5000 words, it counts as a feature article by the standard of any magazine. We have an unmanaged com server application that aggregates a. The interop runtime code will insert the appropriate method calls for reference counting when the managed proxy objects are created and freed, and will translate typecast, is, and as operators into calls to queryinterface.
And when we declare dispinterface someinterce, then it means. The two that you need to know about are idispatch interfaces and idl. It appears that this bug has been submitted via the. The controller must first create the object, then query the objects iunknown interface for a pointer to its idispatch interface. Com automation objects additionally implement the idispatch interface, which includes. Using ccompolyobject avoids having both ccomaggobject and ccomobject in your module. To call a method in a simple iunknown interface all you need is to know where in the vtable the function pointer is. You might wonder how a single interface can expose the functionality of any application.
An iunknown or iunknown derived interface consists of a pointer to a virtual method table that contains a list of pointers to the functions that implement the functions. In classic windows programming, libraries are often implemented as com objects or more precisely, as com servers. Gettypeinfocount can be 1 or 0 and represents the number of type information interfaces that the object provides. Beyond the three inherited methods of iunknown, idispatch defines exactly four functions, and therefore a coclass implementing idispatch must flesh out seven methods. The iunknown interface id is defined as a guid with the value of 0000000000000000c000000000000046 a com components interfaces are required to exhibit the reflexive, symmetric, and transitive properties. The idispatch interface inherits from the iunknown interface. So, today my mind has been 100 % focused on something that on the surface looks really boring. Jan 03, 2010 so, today my mind has been 100 % focused on something that on the surface looks really boring. Iunknown interface provides clients like directx control of to get pointers to other interfaces. I was participating a course at develop mentor where this was the recommandation. Well the best way is to get your idispatch interface directly with its clsid. Jan 24, 2009 to implement multiinterface dispatch on one or more pure iunknown derived interfaces, use puredispatchimpl. Idispatchimplex template classes for multiinterface.
Looks like its not possible to implement iunknown and idispatch interfaces in. The operation of the idispatch interface, like the iunknown interface. The vtable of a dispinterface is identical to that of. An idispatch interface is a special type of iunknown interface that includes methods that allow methods to be called by name at runtime. You can use idelegatingdispimpl instead of idispatchimpl you suggest that we should use when using your cmultidispatch class. Ccompolyobject implements iunknown for aggregated and nonaggregated objects. Vba can define a parameter as being of type iunknown by using a reference to the external library stdole2. You cant change the inheritance list on a published interface anymore that you can change the list of methods or their arguments. An interface based solely on idispatch is called a dispinterface. Every interface must derive directly from iunknown or from an interface that. Crossplatform applications can use interfaces descended from iunknown, but must not use them to access com objects, which are only available under windows. Net world if you developed with office 2000 installed, every developer, and every customer, from now until the end of time, is required to have office 2000. Interface property methods win32 apps microsoft docs. In delphi code, iunknown is simply another name for iinterface.
The routine wants its iunknown interface reference, but delphi can extract that. This allows a client to bind to members at compile time and avoid calling getidsofnames at run time. Handling exceptions in com and automation, the delphi magazine. The rest is just that interfaces are doubly indirected to get to a vtable an array or struct. Exposes objects, methods and properties to programming tools and other applications that support automation. The reflexive property refers to the ability for the queryinterface call on a given interface with the interface s id to return the same instance of the interface. Getidsofnames is used when an idispatch client binds to names at run time. Net class are transformed to dual interfaces in the idl. To call a method in a simple iunknown interface all you need is. To bind at compile time instead, an idispatch client can map names to dispids by using the type information interfaces described in type description interfaces. If an interface b is derived from idispatch we have. Automation clients use the two methods getidsofnames and invoke to achieve late binding. The vtable of a dispinterface is identical to that of idispatch itself. These interfaces are usually dual interfaces, which means they implement idispatch as well.
How can i specify my own implementations of these two interfaces, so that they get called instead of. Descending from iunknown instead of iinterface informs the delphi compiler that the interface must be compatible with com objects. And you may even know that its required by comobjects used in autoit with the objcreate function. Its the basic interface which all com objects must implement. How to implement the idispatch interface expertsexchange. You use different idl attributes depending on whether you are implementing a pure idispatch interface or a dual interface. It is usually not necessary to call iunknown s methods directly in your. As in the case of iunknown, visual basic programmers never deal with this interface directly. Pretend im trying to automate office, while being compatible with whatever version the customer has installed in the.
Iunknown and idispatch are burned permanently in my memory from a. Net component is also responsible for the idispatch interface. When receiving a pointer to an interface, the client is assured that it can call any method of the interface. It is usually not necessary to call iunknowns methods directly in your. The idispatch interface developers workshop to com and atl 3. Enables clients to get pointers to other interfaces on a given object through the queryinterface method, and manage the existence of the object through the addref and release methods. Automation allows components written in different languages to communicate with one another. What is the difference between idispatch and iunkown in com. By continuing to browse this site, you agree to this use. Can some body tell me whether vb uses idispatch or iunknown. The qi to idispatch will increment the refcount of the unmanaged server object by 2.
Com has one interface from which all other interfaces derive. Queryinterface knows about every interface in the server object and can give a client a pointer to the requested interface. Doing so would cause the vtable slots to shift down to make space for the idispatch methods. The software uses the following process to determine which handle to return. Running our code with the beta2 framework now has a refcounting issue that was not. It provides the basic ability to cast a instance of a com object to any of its supported interfaces. Dispinterface is an idispatch plus an agreement on what each dispid means and what parameters it should come with. The idispatch interface developers workshop to com and.
Now, my issue is, the com object uses the idispatch and iunknown interfaces of the object i pass to determine what events to send and to actually send the events. For additional information on how interfaces are exposed to com, see exported type conversion. Iunknown implementation classes atl microsoft docs. To implement multiinterface dispatch on one or more pure iunknownderived interfaces, use puredispatchimpl.
Many windows operating system components are implemented as com servers, and many contributors provide libraries in this form. Most of com objects implement more than one interface. There is a requirement, however, that there is type info available for the interfaces. This site uses cookies for analytics, personalized content and ads. I know that scripting languages can use idispatch only but not sure about vb. The vtable that represents idispatch is shown in figure 37. Vba use the createtypelib2 api function to generate the type library when they build their own com components. Dispatch interfaces automation controllers are clients that use the com idispatch interface to access the com server objects. Jan 03, 2010 an example that is directly relevant for your example is this direct3d example by progandy the direct3d interfaces also only inherits from iunknown. You can found it with its sample source code on windows developer network windows developer magazine archives 1999.
The following classes implement iunknown and related methods ccomobjectrootex manages reference counting for both aggregated and nonaggregated objects. Cmultidispatch multiple idispatch interfaces for automation. However, there may be occasions when you want the interface to be a puredispinterface or a. Net object is destroyed, the refcout is only decremented by 1. A single ccompolyobject object handles both aggregated and nonaggregated cases. Thus, our refcount monitor will think somebody is still using the server and not shut down the local server. Running above client code now has a refcounting issue. A dual interface is simply idispatch with functions pasted onto the end. How can i specify my own implementations of these two interfaces, so that they get called instead of the default system implementation. Iunknown is the base class for all olecomactivex components. It is used in multiple inheritance where the various interfaces can share one implementation of iunknown.
I think vb 5 supports iuknown but vb 4 supports only idispatch. This is the base interface from which every delphi interface inherits, and delphi provides a couple of different classes with readyto. All com objects support the iunknown interface methods of addref. All com interfaces are inherited from iunknown interface. Idispatch is a single physical interface that allows less sophisticated clients to get at any number of logical interfaces. Using the object from scripting automation environments. Idispatch is the interface that exposes the ole automation protocol. This way, the appropriate idispatch method that performs latebound. Of course, you can provide access through both idispatch and through a custom interface, but that involves bookkeeping. Clients obtain pointers to other interfaces through the iunknown method, queryinterface. A dual interface is simply idispatch with functions pasted onto the. Idispatch builds on iunknown adding the facility to discover at runtime the attributes and interfaces supported by the specified com object. If you use such an object from a programming environment that can access iunknown, all the interfaces are available through the queryinterface method. Iunknown exposes two essential features of all com objects.
As you can see, idispatch derives from iunknown like any com compliant interface must do. Did you change your main interface to now inherit from idispatch instead of inheriting from iunknown. In this lesson, you will learn more about how the idispatch interface and the variant data type are used to allow other languages to access com components. From msdn, dispinterface is another interface inherits from idispatch. The idispatch interface was defined so that a single, standard interface 2 could be used by all components wanting to expose their functionality to interested clients.
Extending iunknown, it is one of the standard interfaces that can be exposed by com. Here is the idispatch interface defined in interface definition language idl notation. When you invoke the actxserver function, matlab creates the server and returns a handle to the server interface as a means of accessing its properties and methods. If you were to create a component that simply exports the iunknown interface, you.
You can create class instances with comobjcreate, you can call these instances methods, and you can interact with them in other ways. An example that is directly relevant for your example is this direct3d example by progandy the direct3d interfaces also only inherits from iunknown. Even if you late bind through an idispatch interface, you still need to know what. Ccomobjectnolock implements iunknown for a nonaggregated object, without modifying the module lock count.
Application and id like to cast this idispatch to native documentwindow in order to. Application and id like to cast this idispatch to native documentwindow in order to call its methods and properties not via idispatchinvoke, but directly. Com components implement the idispatch interface to enable access by automation clients, such as visual basic. I can get an iunknown pointer to an object of that class. Implement the idispatch interface in comenabled classes that have to act as automation controllers. Many adsi interfaces are designed to support automation and thus are dual interfaces in that they support client access through both iunknown and idispatch interfaces. In essence, idispatch represents a standard vtable with a highly. But if you want to do that you can use queryinterface to get idispatch pointer but that is not converting you will be getting a new pointer. This allows the client to get the best of both early binding and late binding. Well also look at a standard interface named idispatch, and youll see how objects provide access to scripting clients through the use of a com mechanism called automation. How to cast dual interfaces of microsoft powerpoint. Every com object must implement the iunknown interface, also dubbed iinterface in delphi for noncom usage of interfaces as you saw in chapter 2.
Com object interfaces iunknown and idispatch interfaces. I have a dual idispatch interface of documentwindow class, related to powerpoint. How to cast dual interfaces of microsoft powerpoint classes. Therefore, the three methods in iunknown are the first entries in. Automation controllers are clients that use the com idispatch interface to access the com server objects. Before we begin looking at an example of com development, ill introduce a few com basics.
94 690 591 1230 819 517 636 1291 715 246 496 330 835 1388 1429 1527 26 1260 124 1404 146 1460 1128 1479 138 1031 1347 873 38 568 400 1136 578 631 1159 1312 1174 1458 700 1294 1384