There are two com interfaces above the autocad object model that are essential to its operation. Createcomobject returns an object of the iunknown type, whereas createoleobject returns an object of the idispatch type. To better understand how the idispatch interface works, it is helpful to think of it as a kind of surrogate interface. Set x y, and set is used for regular value assignment, e.
The idispatch interface exposes a number of methods for automation clients that require latebinding such as scripting languages. The only essential difference between figure 12b and c is the length of the connecting fiber. Obtain type information of idispatchbased com objects. Iunknown is the base interface for every com class. The object data types is the core connection between vba and com. I suspect i am missing something, but i dont know from where to pull the idispatch definition in. Idispatch, the main interface in automation is described. This chapters deals with the similarities and differences between objects and interfaces.
If the renewal price changes, we will notify you in advance so you always know whats going on. Net framework sdk and can be found under the bin subfolder of your sdk. Com calbacks idl idispatch vs dispinterface too old to reply bigfish 20050831 04. In delphi code, iunknown is simply another name for iinterface. This type of implementation creates what is known as a singleton object since there. The reflexive property refers to the ability for the queryinterface call on a given interface with the interfaces id to return the same instance of the interface. Now instead of deriving from iunknown, the isum interface derives from idispatch, which is itself derived from iunknown, so we still get the queryinterface, addref, and release methods added to the vtable. Jun 28, 2010 an idispatch interface is a special type of iunknown interface that includes methods that allow methods to be called by name at runtime.
Authoring and consuming classic com components with wrl. Inheritance is a very important concept in oo programming. Iunknown methods can be used to switch between interfaces on an object, add references, and release objects. You use different idl attributes depending on whether you are implementing a pure idispatch interface or a dual interface. Iunknown definition at archived 20711 at the wayback machine. If you know visual basic, then the easiest way to explain it is that setref is used for vbs set keyword, e. The difference between set and setref is subtle and annoying. The idispatch interface inherits from the iunknown interface. Gettypeinfocount can be 1 or 0 and represents the number of type information interfaces that the object provides gettypeinfo returns the type information for the object. All com interfaces derive from the iunknown interface, and all com objects.
Idispatch builds on iunknown adding the facility to discover at runtime the attributes and interfaces supported by the specified com object. The type or namespace name idispatch could not be found are you missing a using directive or an assembly reference. And when we declare dispinterface someinterce, then it means someinterface. That is, you can use an instance of a smart pointer class in many of the places you normally use a pointer. When you implement one or more userdefined interfaces in a class, visual basic provides an implementation of queryinterface that allows clients to move among interface references. Idispatch doesnt offer any functionality of its own. Base interfaces iunknown and idispatch are stripped type definitions are not imported. When you create the server object, you get as a return value an ifirstserver interface.
Its an ambassador of goodwill between the managed world and the unmanaged iunknown world. A lot of you probably heard the name idispatch before. Programmers are not allowed to use an iunknown data type from vba this is a hidden data type. In addition to the methods inherited from iunknown, server. Explain some of commonly used methods provided by iunknown. The vtable that represents idispatch is shown in figure 37. The separation between declaration and implementation is discussed. Component object model com is a binaryinterface standard for software components introduced by microsoft in 1993. Net framework data provider for ado and ole db system. Well the best way is to get your idispatch interface directly with its clsid.
Which brings us to the last, and most interesting, part of this exercise. It provides the basic ability to cast a instance of a com object to any of its supported interfaces queryinterface. However, using a smart pointer provides some advantages over using a raw pointer. Comnet object, stored in a 32bit address for the com interface. It provides the basic ability to cast a instance of a com object to any of its supported interfaces. First we ask for the actual hresult value, as an int. I read some msdn document and some other forum discussions about the differences between idispatch and dispinterface, but still confused. Lets generate the metadata wrapper for our airline com component. It is used to enable interprocess communication object creation in a large range of programming languages. On the client side the difference between an interface and an object is only small. Sep 16, 20 these include comptr a smart pointer type that represents the interface t, runtimeclass represents an instantiated class that inherits one or more interfaces, implements iunknown s methods and helps manage the overall reference count of the module and module a collection of objects that i will use in the further paragraphs for creating. Therefore, it will not be very efficient on other platforms. A smart pointer is an object that behaves like a pointer.
A unique number, called a dispatch identifier dispid, identifies each method. The typed accessor methods for the oledbdatareader are also listed. But just as you no longer need to understand assembly language to get software working these days, pretty soon, youll no longer need to understand all the nuances of iunknown and com to. The two that you need to know about are idispatch interfaces and idl. Net object type can be obtained from progid or clsid. 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.
Setref sets the value of a property to be a reference to the passedin value. Use iunknown methods to switch between interfaces on an object, add references, and release objects. 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. But it does extend the reach to other platforms compared to activex components. Idispatch itself inherits from iunknown and that is the root interface of com. An idispatch interface is a special type of iunknown interface that includes methods that allow methods to be called by name at runtime. Idispatch interface and accessibility win32 apps microsoft docs.
Idispatch is the interface that exposes the ole automation protocol. Idispatch gettypeinfo, retrieves the type information for an object, which can. Another unit is also created in the project which contains pascal representations of the entities defined in the type. Lets start with a quick recapitulation of object oriented programming. Object can be exposed to unmanaged code as one of the following types.
From msdn, dispinterface is another interface inherits from idispatch. The iunknown interface lets clients get pointers to other interfaces on a given object through the queryinterface method, and manage the existence of the object through the iunknownaddref and iunknownrelease methods. Idispatchgettypeinfo, retrieves the type information for an object, which can. It is usually not necessary to call iunknown s methods directly in your. What is the difference between idispatch and iunkown in com. These notes apply specifically to the case where the unknown type is iunknown. Unless otherwise stated, if a savings amount is shown, it describes the difference between the first term and renewal term subscription prices e. This is the biggest difference between the three translations we derived for queryinterface what type of value they returned. Descending from iunknown instead of iinterface informs the delphi compiler that the interface must be compatible with com objects. If you are using nested classes to implement multiple interfaces, you must implement iunknown once for each interface you implement.
The vtable of a dispinterface is identical to that of idispatch itself. The central idispatch method is idispatch invoke, which a client calls to invoke a particular method in the component. Net also provides the ability to make use of late binding through the idispatch interface of a com object see listing 5. Notice that in the idl fragment, the syntax seems more standard. Best collection of com, dcom, activex tutorials, topics. But if you want to do that you can use queryinterface to get idispatch pointer but that. 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. And you may even know that its required by comobjects used in autoit with the objcreate function. It is usually not necessary to call iunknowns methods directly in your. To do that, we need to use a tool called the tlbimp.
As in the case of addref and release, the visual basic implementation of queryinterface is fairly straightforward, but you can never see it. Idispatch this interface provides namebased dynamic method dispatch for ole automation com objects. The purpose of an idispatch interface is to provide an interface for use with scripting clients. In computer programming, the iunknown interface is the fundamental interface in the. Since the information needed for implementing idispatchinvoke is in the type library, its sensible to use the type library to implement idispatchinvoke.
Automation relies on an interface named idispatch, which allows clients to create method bindings at runtime in a process known as late binding. 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 declared in the interface, in the order that they are declared in the interface. To call a method in a simple iunknown interface all you need is to know where in the vtable the function pointer is. The iunknown interface lets clients get pointers to other interfaces on a given object through the queryinterface method, and manage the existence of the object through the iunknown addref and iunknown release methods.
Iunknown implementations are generally the same for every com class you encounter the main difference between them is the interfaces exposed by each class. I think vb 5 supports iuknown but vb 4 supports only idispatch. So, today my mind has been 100 % focused on something that on the surface looks really boring. Another unit is also created in the project which contains pascal representations of the entities defined in the type library. Contribute to go olego ole development by creating an account on github.
Vba can define a parameter as being of type iunknown by using a reference to the external library stdole2. The idispatch interface has methods that allow clients to ask the object what. Obtain type information of idispatchbased com objects from. An interface based solely on idispatch is called a dispinterface. Here is the idispatch interface defined in interface definition language idl notation. For objects that support idispatch, the type information count is always one. There is another difference between these two creation functions. Only com interop supports marshaling for object types. Extending iunknown, it is one of the standard interfaces that can be exposed by com objects. The central idispatch method is idispatchinvoke, which a client calls to invoke a particular method in the component.
136 872 909 1221 587 1399 66 1107 1170 1383 1325 349 468 459 1487 907 1073 807 760 968 1391 276 1182 886 28 107 170 1198 30 1380 1633 1232 1230 528 451 443 1143 348 1342 969 1097 1064 658 515 206 1311 412