Difference between iunknown and idispatch login

And when we declare dispinterface someinterce, then it means. There is another difference between these two creation functions. Calling functions and accessing properties apache openoffice wiki. Idispatch is the interface that exposes the ole automation protocol. Explain some of commonly used methods provided by iunknown. Whats the difference between thread and process, exe, dll and mtdll, earlybinding and latebinding, between vtable and idispatch. The implementation adds a single idispatch implementation to the class, and uses typeinfo to dispatch against the pure interfaces. Iunknown implementations are generally the same for every com class you encounter the main difference between them is the interfaces exposed by each class. In atl, idispatchinvoke is implemented by idispatchimpl. Every com class implements an interface named iunknown. In addition, atl appears to be getting easier to use as it matures. However, the efficiency difference between using a unicode string and an. All other interfaces must derive directly or indirectly from iunknown. The idispatch interface has methods that allow clients to ask the object what.

Only some classes support idispatch which derives from iunknown. 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. Cdispatchptr is a subclass of idispatchptr, with the getsetsetrefinvoke methods added. The idispatch interface was initially designed to support automation. The only difference between early binding and late binding in terms of the code you write is in the variable declaration. When the property is an iunknown,idispatch, or safearray, the flag. The idispatch interface allows many scripting languages to control the com objects methods and properties using runtime method calls to idispatch a method call dispatching interface. As in the case of iunknown, visual basic programmers never deal with this interface directly. The vtable that represents idispatch is shown in figure 37. An idispatch interface is a special type of iunknown interface that includes methods that allow methods to be called by name at runtime. From msdn, dispinterface is another interface inherits from idispatch. Idispatch, the main interface in automation is described.

There is a special type of com server, where the com objects support the idispatch interface, called an automation server. Vba can define a parameter as being of type iunknown by using a reference to the external library stdole2. The object data types is the core connection between vba and com. What is the difference between idispatch and iunkown in com. This new unit needs to define a class that will act as the event sink. Iunknown methods can be used to switch between interfaces on an object, add references, and release objects. Net framework view topic how to implement idispatch. Hi, whats the difference between an interface declared with. Visual foxpro developers make no differences between defining a class and implementing it. There is a requirement, however, that there is type info available for the interfaces.

Can somebody tell me what is the difference between the methods and the functions in atl. 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. The differences between the two architectures are fairly stark. Implement the idispatch interface in comenabled classes that have to act as automation controllers. The two that you need to know about are idispatch interfaces and idl. It is through the iunknown interface that clients maintain a reference on an.

Lets start with a quick recapitulation of object oriented programming. Com component object model com is microsofts component software architecture developed primarily for windows. The idispatch interface extends the iunknown interface and is a sort of gateway interface to many more interfaces grimes97. It is important to note that what is late bound is the function being called and not the way it is called. Class objects in an exe server has one difference from those in a dll server. Idispatch derives from iunknown and extends its set of three methods addref, release and queryinterface with an additional four methods gettypeinfocount, gettypeinfo, getidsofnames and invoke. Well the best way is to get your idispatch interface directly with its clsid. How can i specify my own implementations of these two interfaces, so that they get called instead of the default system implementation. The idispatch interface exposes a number of methods for automation clients that require latebinding such as scripting languages. Dispinterface is an idispatch plus an agreement on what each dispid means and what parameters it should come with. In this video we learn about the iunknown interface the one interface all com objects must implement. Idispatchimplex template classes for multiinterface.

Notice that in the idl fragment, the syntax seems more standard. This chapters deals with the similarities and differences between objects and interfaces. To call a method in a simple iunknown interface all you need is to know where in the vtable the function pointer is. It is the foundation upon which ole and activex are based, and provides a means to reuse code without requiring recompilation. This is the only real difference between a dispinterface and a dual interface.

Tinterfacedobject implements the three iunknown methods already so that is a suitable class to inherit from, however we must reimplement the queryinterface method to indicate runtime support for the events interface as well. If we dont use object and use a comimport interface you. While its a very simple interface, compared to some of the others well get to later, it does highlight a number of interesting and important behaviors that the. Gettypeinfocount can be 1 or 0 and represents the number of type information interfaces that the object provides. The following is a list of tips and tricks that might be useful to com developers of all levels. Programmers are not allowed to use an iunknown data type from vba this is a hidden data type. Note the only difference between com and dcom is the connection between the client and the server. According to the oxford dictionary, both spellings are synonymous for all meanings of the word. The essence of automation objects is the idispatch interface. What methods are provided by iunknown answer cheruku raghu. Use early binding and late binding in automation office. I can get their window handles via regular api calls, and can get other basic info about them based on the api calls as well, but need to actually obtain a pointer to the object so that i can manipulate it, etc. Observe that assigning a t to a ccomptr addrefs the incoming pointer and releases the old pointer if any. The separation between declaration and implementation is discussed.

So i think it unlikely that the iideaclientopendatabase method returns anything other than idispatch. Idispatch builds on iunknown adding the facility to discover at runtime the attributes and interfaces supported by the specified com object. Atl isnt quite as quick and easy to use, but it is comfriendly. Iunknown and retval rewriting today, were going to finish out the definition of iuknown that we started last time, by adding the three methods to the interface.

However, dispatch is more common in american english and despatch seems to be. Difference between ccomptr and ccomqiptr 140 difference between ccomptr and ccomqiptr vcwebbrowserie mfc activex com. It provides the basic ability to cast a instance of a com object to any of its supported interfaces. 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. Format differences like byte ordering and number representations are bridged this way.

What is the difference between dispatch and despatch answers. 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. If you have an interesting tip thats not listed here, please submit it to me and ill add it to the list if i think its useful. This type of implementation creates what is known as a singleton object since there is. Of course, you can provide access through both idispatch and through a custom interface, but that involves bookkeeping. What is the difference between method and function.

This session requires basic knowledge of memory adresses, pointers and data storage. 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. It is a generally good idea to have an answer for this question if you claim you know com in your resume. To implement multiinterface dispatch on one or more pure iunknown derived interfaces, use puredispatchimpl. 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. Iunknown is the base interface for every com class. All object manipulation through strict interfaces polymorphism iunknown via multiple interfaces per class idispatch discoverable. Automation clients use the two methods getidsofnames and invoke to achieve late binding. When the ccomptr is destructed, it will release the pointer, undoing the addref that was performed by the assignment operator. Implementing the idispatch interface microsoft docs. Extending iunknown, it is one of the standard interfaces that can be exposed by com objects. The interface header also includes the dual attribute to indicate a dual interface. For automation and active server objects, the wizard implements iunknown and idispatch, which provides automatic marshaling. Idispatch interface and accessibility win32 apps microsoft docs.