Idispatchgetidsofnames is called by a client that has a method name sum. Idispatch must consult the type library associated with the automation controller in order to resolve function calls at runtime. Idispatch builds on iunknown adding the facility to discover at runtime the attributes and interfaces supported by the specified com object. Automation clients use the two methods getidsofnames and invoke to achieve. I am using the function idispatch getidsofnames to get ids on methods and their parameters to then pass on to idispatch 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.
String rgsznames, int cnames, int lcid, int rgdispidgettypeinfo public int gettypeinfoint itinfo, int lcid, int pptinfo. Idispatch interface is used to support type info and additional functions. Getidsofnames can translate the function name to a numerical identity. Queryinterfacegettypeinfocount,gettypeinfo, getidsofnames. Iunknown is responsible for life cycle management and providing clients with an interface to some piece of desired functionality. The vtable of a dispinterface is identical to that of idispatch itself.
The getidsofnames function can be used to get the appropriate dispid from a property or method name that is in string format. Thats what happens when you use variants for oleautomation in delphi the only interface you are using is the idispatch 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. The idispatch interface exposes methods and properties for automation.
As in the case of iunknown, visual basic programmers never deal with this interface directly. Getidsofnames public int getidsofnames guid riid, string rgsznames, int cnames, int lcid, int rgdispid. Lets start with a quick recapitulation of object oriented programming. Extending iunknown, it is one of the standard interfaces that can be exposed by com objects. Ccomdispatchdriver has an overloaded constructor that takes an iunknown pointer argument and queries for idispatch. Getidsofnames public int getidsofnames guid riid, java.
Implementing the idispatch interface microsoft docs. Automation controllers are clients that use the com idispatch interface to access. The definitions of iunknown s queryinterface and the set of idispatch methods can be found in the system. Below four functions will be added after those three entries.
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. The definitions of iunknowns queryinterface and the set of idispatch methods can be found in the system. Getidsofnames is used primarily to obtain dispatch identifiers for the latebinded methods exposed by the com object through the idispatch interface. 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. The idispatch interface exposes a number of methods for automation. I read some msdn document and some other forum discussions about the differences between idispatch and dispinterface, but still confused. Here is the idispatch interface defined in interface definition language idl notation. Simplifying idispatchinvoke inside atl programming. 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. Idispatch is the interface used to support automation. An interface based solely on idispatch is called a dispinterface. Queryinterface addref release interface iunknown operations. Idispatch, queryinterface, cocreateinstance, iunknown, gettickcount, itoa, atl control by ranjan banerji. Idispatch itself inherits from iunknown and that is the root interface of com. Idispatch public idispatchint address method detail.
Idispatch iwastedtimeonthis but ilearntlots productive rage. The idispatch interface inherits from the iunknown interface. Getidsofnames returns an integer id representing the method name. The documentation for this interface was generated from the following file. The dispids are generated by the bridge, as required. Gettypeinfocount can be 1 or 0 and represents the number of type information interfaces that the object provides. 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. This id can be passed to invoke call to call the actual function. In fact, the genius of idispatch is that it was defined using just four methodsgettypeinfocount, gettypeinfo, getidsofnames, and invoke. 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. Getidsofnames public int getidsofnames guid riid, string rgsznames, int cnames, int lcid, int rgdispid gettypeinfo public int gettypeinfoint itinfo, int lcid. The code shown below shows this interface, it has four functions.
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. Idispatch getidsofnames, maps a single member and an optional set of. The separation between declaration and implementation is discussed. Addref, release, queryinterface it implements gettypeinfocount, gettypeinfo, getidsofnames and invoke. String rgsznames, int cnames, int lcid, int rgdispid. Atls implementation of idispatch lives in the class idispatchimpl. You can enumerate the methods an idispatch exposes through the type info. Contribute to go olego ole development by creating an account on github. The base run time library for elements native windows and linux platform, codenamed island.
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 provides the basic ability to cast a instance of a com object to any of its supported interfaces queryinterface. The following examples show how to access an activex or ole object through the idispatch interface. Dispid rgdispid return ptypeinfogetidsofnamesrgsznames. When the property is an iunknown,idispatch, or safearray, the flag. How to add dispatching for a com object that does not implement. Activex or ole objects can implement the idispatch interface for access by. It derives from iunknown and offers an additional four methods. Automation relies on an interface named idispatch, which allows clients to create method bindings at runtime in a process known as late binding.
And when we declare dispinterface someinterce, then it means someinterface. This vtable runtime binding mechanism cannot work for scripting languages. Com components implement the idispatch interface to enable access by automation clients, such as visual basic. You can store the object reference in a variant variable or use a dispinterface type. Gettypeinfocount, gettypeinfo, getidsofnames, and invoke. To call a method in a simple iunknown interface all you need is to know where in the vtable the function pointer is. Idispatch derives from iunknown and extends its set of three methods addref, release and queryinterface with four more methods gettypeinfocount, gettypeinfo, getidsofnames and invoke. This chapters deals with the similarities and differences between objects and interfaces. Jun 28, 2010 the two that you need to know about are idispatch interfaces and idl. Automation in delphi com programming defining automation. Gettypeinfocount, gettypeinfo, getidsofnames and invoke. From msdn, dispinterface is another interface inherits from idispatch. I can get the function to work on methods that do not accept any parameters i. The two that you need to know about are idispatch interfaces and idl.
Getidsofnames returns a set of dispatch identifiers dispid s for a given member name. The automation idispatch interface allows a client application to find out what properties and methods are supported by an object at runtime. Calling functions and accessing properties apache openoffice wiki. Idispatch public idispatch int address method detail. So queryinterface, addref and release virtual functions will be at the top of the vtable entries. 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. The idispatch interface was designed to call a function using com. Activex or ole objects can implement the idispatch interface for access by activex clients, such as visual basic. Similar to ccomqiptr, ccomdispatchdriver implements the necessary operator overloading that allows it to be used anywhere idispatch is required. Getidsofnames is able to map a name to an internal id.
The essence of automation objects is the idispatch interface. Sep 11, 2006 it derives from iunknown and offers an additional four methods. Atls implementation of idispatch is similar to the approach just outlined. Idispatchgetidsofnames maps a single member and an optional set of. 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. 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. The idispatch interface exposes a number of methods for automation clients that require latebinding such as scripting languages. Interface idispatch exposes objects, methods and properties to programming tools and other applications that support automation. Automation clients use the two methods getidsofnames and invoke to achieve late binding. 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. Idispatch derives from iunknown and extends its set of three methods addref. 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.
1230 876 106 557 1242 1617 1506 1596 1633 562 106 1329 126 573 253 345 551 797 380 835 61 333 589 526 751 549 1611 1156 461 1575 110 704 1388 295 175 197 605 950 1208 846 582 306