The definitions of iunknowns queryinterface and the set of idispatch methods can be found in the system. Getidsofnames public int getidsofnames guid riid, string rgsznames, int cnames, int lcid, int rgdispid. Automation relies on an interface named idispatch, which allows clients to create method bindings at runtime in a process known as late binding. The vtable of a dispinterface is identical to that of idispatch itself. Activex or ole objects can implement the idispatch interface for access by activex clients, such as visual basic. The dispids are generated by the bridge, as required. Queryinterfacegettypeinfocount,gettypeinfo, getidsofnames. The essence of automation objects is the idispatch interface. It is easiest to copy all the method declarations into the class definition along with a method resolution clause to allow queryinterface to be redefined as shown in listing 12, then use class completion to finish off. To call a method in a simple iunknown interface all you need is to know where in the vtable the function pointer is.
Idispatch getidsofnames, maps a single member and an optional set of. Thats what happens when you use variants for oleautomation in delphi the only interface you are using is the idispatch interface. In fact, the genius of idispatch is that it was defined using just four methodsgettypeinfocount, gettypeinfo, getidsofnames, and invoke. As a matter of fact, what happens is the following.
The objects properties and methods can be accessed using idispatch getidsofnames and idispatch invoke. Idispatch interface is used to support type info and additional functions. The vtable that represents idispatch is shown in figure 37. String rgsznames, int cnames, int lcid, int rgdispidgettypeinfo public int gettypeinfoint itinfo, int lcid, int pptinfo. The idispatch interface exposes a number of methods for automation clients that require latebinding such as scripting languages. The following examples show how to access an activex or ole object through the idispatch interface. Idispatchgetidsofnames maps a single member and an optional set of. I can get the function to work on methods that do not accept any parameters i. This id can be passed to invoke call to call the actual function. How to add dispatching for a com object that does not implement. Getidsofnames is able to map a name to an internal id. The idispatch interface inherits from the iunknown interface.
Idispatch public idispatchint address method detail. Idispatch must consult the type library associated with the automation controller in order to resolve function calls at runtime. Similar to ccomqiptr, ccomdispatchdriver implements the necessary operator overloading that allows it to be used anywhere idispatch is required. As in the case of iunknown, visual basic programmers never deal with this interface directly. Idispatch, the main interface in automation is described. Idispatch, queryinterface, cocreateinstance, iunknown, gettickcount, itoa, atl control by ranjan banerji. Extending iunknown, it is one of the standard interfaces that can be exposed by com objects. Maps a single member and an optional set of argument names to a corresponding set of integer dispids, which can be used on subsequent calls to invoke. This chapters deals with the similarities and differences between objects and interfaces. You can store the object reference in a variant variable or use a dispinterface type to write a com server that implements the idispatch interface, simply derive your class from tautoobject in the comobj unit or one of.
Getidsofnames ref guid, string, int32, int32, int32 maps a single member and an optional set of argument names to a corresponding set of integer dispids, which can. Automation controllers are clients that use the com idispatch interface to access. The code shown below shows this interface, it has four functions. Idispatch getidsofnames is called by a client that has a method name sum, for example and wants to get the dispid associated with that method to call it via idispatch invoke. Idispatch is the interface that exposes the ole automation protocol. The idispatch interface exposes a number of methods for automation.
Here is the idispatch interface defined in interface definition language idl notation. It provides the basic ability to cast a instance of a com object to any of its supported interfaces queryinterface. The base run time library for elements native windows and linux platform, codenamed island. Idispatch itself inherits from iunknown and that is the root interface of com. So queryinterface, addref and release virtual functions will be at the top of the vtable entries. An interface based solely on idispatch is called a dispinterface.
You can enumerate the methods an idispatch exposes through the type info. Getidsofnames public int getidsofnames guid riid, string rgsznames, int cnames, int lcid, int rgdispid gettypeinfo public int gettypeinfoint itinfo, int lcid. Jun 28, 2010 the two that you need to know about are idispatch interfaces and idl. Gettypeinfocount can be 1 or 0 and represents the number of type information interfaces that the object provides. Atls implementation of idispatch is similar to the approach just outlined. Com components implement the idispatch interface to enable access by automation clients, such as visual basic. When you use a com object that implements the idispatch interface, delphi automatically takes care of all the details involved in calling a method dynamically. First the com id for the method name createinstance is retrieved from getidsofnames, then the id is used to invoke the method createinstance before calling a certain function on the idispatch interface, get the dispid by calling getidsofnames. It derives from iunknown and offers an additional four methods. Atls implementation of idispatch lives in the class idispatchimpl. Gettypeinfocount, gettypeinfo, getidsofnames, and invoke. Gettypeinfocount, gettypeinfo, getidsofnames and invoke.
Activex or ole objects can implement the idispatch interface for access by. This vtable runtime binding mechanism cannot work for scripting languages. From msdn, dispinterface is another interface inherits from idispatch. Automation clients use the two methods getidsofnames and invoke to achieve. Calling functions and accessing properties apache openoffice wiki. The definitions of iunknown s queryinterface and the set of idispatch methods can be found in the system. Queryinterface addref release interface iunknown operations. Idispatch iwastedtimeonthis but ilearntlots productive rage. Automation in delphi com programming defining automation. An idispatch interface is a special type of iunknown interface that includes methods that allow methods to be called by name at runtime. When the property is an iunknown,idispatch, or safearray, the flag. Sep 11, 2006 it derives from iunknown and offers an additional four methods. And when we declare dispinterface someinterce, then it means someinterface.
Idispatch derives from iunknown and extends its set of three methods addref, release and queryinterface with four more methods gettypeinfocount, gettypeinfo, getidsofnames and invoke. Idispatch is the interface used to support automation. Interface idispatch exposes objects, methods and properties to programming tools and other applications that support automation. The idispatch interface exposes methods and properties for automation. String rgsznames, int cnames, int lcid, int rgdispid. The objects properties and methods can be accessed using idispatch getidsofnames and idispatchinvoke the following examples show how to access an activex or ole object. The documentation for this interface was generated from the following file.
The automation idispatch interface allows a client application to find out what properties and methods are supported by an object at runtime. The automation idispatch interface allows a client application to find out what properties and methods are supported by an object at runtime, i. Idispatch is the pascal definition of the windows dispatch interface definition see also. Getidsofnames returns a set of dispatch identifiers dispid s for a given member name. Getidsofnames returns an integer id representing the method name.
Dispid rgdispid return ptypeinfogetidsofnamesrgsznames. Ccomdispatchdriver has an overloaded constructor that takes an iunknown pointer argument and queries for idispatch. Idispatch derives from iunknown and extends its set of three methods addref. Getidsofnames is used primarily to obtain dispatch identifiers for the latebinded methods exposed by the com object through the idispatch interface. The idispatch interface was designed to call a function using com. 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. Getidsofnames can translate the function name to a numerical identity.
Addref, release, queryinterface it implements gettypeinfocount, gettypeinfo, getidsofnames and invoke. The separation between declaration and implementation is discussed. Implement the idispatch interface in comenabled classes that have to act as automation controllers. Lets start with a quick recapitulation of object oriented programming.
Below four functions will be added after those three entries. There is no fixed mapping from member names to dispids, that is, the. The idispatch interface would have to contain an infinite number of methods. Iunknown is responsible for life cycle management and providing clients with an interface to some piece of desired functionality. I have tried to declare idispatch using its guid and implement it, but the runtime either seems to provide its own idispatch implementation or none at all depending on classinterface attribute of the class.
You can store the object reference in a variant variable or use a dispinterface type. Automation clients use the two methods getidsofnames and invoke to achieve late binding. I read some msdn document and some other forum discussions about the differences between idispatch and dispinterface, but still confused. It is one of the standard interfaces that can be exposed by com objects idispatch derives from iunknown and extends its set of three methods addref, release and queryinterface with four more methods gettypeinfocount, gettypeinfo, getidsofnames and invoke. You use different idl attributes depending on whether you are implementing a pure idispatch interface or a dual interface. I am using the function idispatch getidsofnames to get ids on methods and their parameters to then pass on to idispatch invoke. Idispatch builds on iunknown adding the facility to discover at runtime the attributes and interfaces supported by the specified com object. Getidsofnames public int getidsofnames guid riid, java. Simplifying idispatchinvoke inside atl programming. Implementing the idispatch interface microsoft docs. The two that you need to know about are idispatch interfaces and idl. Idispatch public idispatch int address method detail. Calling idispatchgetidsofnames for functions with one or. Idispatchgetidsofnames is called by a client that has a method name sum.
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