The most important part of this interface is the idispatchinvoke function. In fact, the genius of idispatch is that it was defined using just four methodsgettypeinfocount, gettypeinfo, getidsofnames, and invoke. Stdmethodinvokedispid dispidmember, refiid riid, lcid lcid, word wflags, dispparams pdispparams. When i try to read back the variant and lpdispatch object values from the safearrays, only the first value in each of the arrays is returned. By arnaud aubert, january 01, 2002 using features of the idispatch, arnaud creates a component that sets pixel colors in a bitmap, writes the bitmap into a stream, and stores the picture in a bmp file. An ansi character string that is a lengthprefixed single byte. When the property is an iunknown,idispatch, or safearray, the. Specifying safearray parameters with coledispatchdriver. And you may even know that its required by comobjects used in autoit with the objcreate function. To shield you from the complexities of the invoke parameter sequence, coledispatchdriver has several member functions, including invokehelper, getproperty and setproperty. When you have to consume a managed component in native code, there are basically two options. Having to call both idispatchgetidsofnames to get the dispatch ids. Setting up parameter for idispatchinvoke when calling ref byte. Using example from my first letter, how rewrite it with jicallobject.
There is no fixed mapping from member names to dispids, that is, the. For example, if a script engine inside a browser makes an invokeex call to an external object, the object can follow the pspcaller chain to obtain services from the script engine or browser. An interface based solely on idispatch is called a dispinterface. Setting up parameter for idispatch invoke when calling ref byte. These three functions call invoke for an idispatch pointer that links to the component. Obtain type information of idispatchbased com objects. The dispids are generated by the bridge, as required. When my task is in the servers hands, it processes it and maybe, it will need my intervention. Jan 03, 2010 so, today my mind has been 100 % focused on something that on the surface looks really boring. So, for example, invoking a method ifoohello could very likely delegate to a.
The next example shows the same call realized with helper classes from. To implement an unregistered interface, you can use the idispatchimpl class without accessing the registry by using a predefined version number. The vtable of a dispinterface is identical to that of idispatch itself. The most important part of this interface is the idispatch invoke function. Note that the call chain is not the same as the creation chainalso known as container chain or site chain.
First, obtain a dispid, then call idispatchinvoke with the proper arguments. The variants parray field is a pointer to a safearray. A lot of you probably heard the name idispatch before. Call queryinterface to see if object supports idispatch. I cant use ireflect interface here due to design issues, i need to handle getidsofnames and invoke manually. All function calls, including the access to properties, ultimately require a call to idispatch invoke. The dispids that identify members are defined by the implementor of the object and can be determined by using the objects documentation, the idispatch. Idispatch invoke both to transmit and receive parameters. In this context, a com object is an object that the create com object method instantiates. I try to use it to pass an safearray to safearray in idl parameter, like this. The master is the automation client and the slave is the automation component server.
A unique number, called a dispatch identifier dispid, identifies each method. 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. Obtain type information of idispatchbased com objects from. To use the dispid dispatch identifier of a com method to call that com method, you make an idispatchinvoke call in the com technology. Idl provides several attributes for specifying arrays in com interfaces. The actual declartion depends on the perlanguage documentation youre looking at. Calling functions and accessing properties apache openoffice wiki. So, today my mind has been 100 % focused on something that on the surface looks really boring. The different data types you can store in a safearray are identified as level78 data items in copyfile olesafea. If we have a method that is described in idl like this. Im a client, and i enqueue a task which describes what i want the server to do in the dispatcher. I have used idispatch interface the invoke the property visible. One workaround to this issue would be to modify the invoke implementation in multidisp. For example, the following code calls createinstancecom.
Writing com clients with late and early binding dr dobbs. The argument psa was not a valid safe array descriptor. Reflection with idispatchbased com objects codeproject. Increments the lock count of an array, and retrieves a pointer to the array data. The return value of a function alled through idispatch.
The central idispatch method is idispatchinvoke, which a client calls to. This call will return to us a pointer to an itypeinfo interface which is the gateway to obtaining various type information of an idispatchbased com object. A dynamic type that determines the type of an object at run time and marshals the object as that type. Implementing the idispatch interface microsoft docs. For example, the inkrectangle and inktransform objects are used in. The central idispatch method is idispatch invoke, which a client calls to invoke a particular method in the component. The idispatch interface is the means by which applications expose methods and properties such that other applications such as visual basic, or other languages, can make use of the applications features. The objects properties and methods can be accessed using idispatch getidsofnames and idispatch invoke. Input and returned arrays are marshaled as safearray and ref and. Passing a reference to a safearray as parameter to a.
The autowrap function simplifies most of the lowlevel details involved with using idispatch directly. The client initiates the interaction by constructing a component object it might have to load the component program or by. Dobbs features articles, source code, blogs,forums,video tutorials, and audio podcasts, as well as articles from dr. Mar 18, 2016 the return value of a function alled through idispatch. Increases the pinning reference count of the descriptor for the specified safe array by one, and may increase the pinning reference count of the data for the specified safe array by one if that data was dynamically allocated, as determined. Activex or ole objects can implement the idispatch interface for access by activex clients, such as visual basic. Following is an example of such a modification to the method in multidisp. A clearly defined masterslave relationship is always present in an automation communication dialog. For example, the member names for com interfaces will never be localized. My problem is that the marshaller does not bring back the array afterwards.
The dispidmember argument identifies the member to invoke. Here is the idispatch interface defined in interface definition language idl notation. Example on creating your own idispatch implementation github. My code is more difficult, but i show a simple example, which also does not worke. For maximum generality, the parameters would be passed as a variable length array of the polymorphic variant types, and the invoke method would return a variant. If you create an idispatchimpl object that has 0xffff as the value for wmajor and 0xffff as the value for wminor, the idispatchimpl class retrieves the type library from the. The idispatch interface would have to contain an infinite number of methods. I am setting up a variant as a parameter to idispatchinvoke. Example on creating your own idispatch implementation idispatch. Note that the call chain is not the same as the creation chainalso known as. Software tools and techniques for global software development.
In an activex client, invoke should be used to get and set the values of properties, or to call a method of an activex object. How to pass safearray to com object through idispatch. This call will return to us a pointer to an itypeinfo interface which is the gateway to obtaining various type information of an idispatch based com object. This page was last modified on 28 march 2012, at 19. If the answer was yes an id would be passed back, which could then be fed into method invoke with the parameters, if any, to execute the required action. Problem converting variant and idispatch array into safearray. The most serious of these problems is the performance of idispatch based components.
Instead, call invoke with the dispids supplied in the sdk headers. Aug 04, 2016 passing a reference to a safearray as parameter to a managed com event handler part 2. The automation idispatch interface allows a client application to find out what properties and methods are supported by an object at runtime, i. Setting up parameter for idispatchinvoke when calling. The essence of automation objects is the idispatch interface. Safearray, safearray, a standard visual basic array, com. Cmultidispatch multiple idispatch interfaces for automation. The question of how to pass a safearray to a com object through idispatch is useful me to in circumstances besides icryptotransform. I have used cocreateinstance and i have not used any atl classes in this sample code. Yes definitely, the way you are doing is thru idispatch, and is called latebinding and your client is called agnostic client, because you determine functions at runtime using getidsofname and invoke methods thru idispatch table.
Components using idispatch can be accessed in two slightly different ways, known as early binding and late binding. Portions of the code are omitted for brevity, including handling any errors returned by function calls. Some languages provide automatic mechanisms to invoke methods through an idispatch interface at runtime i. Jan 07, 20 reflection with idispatch based com objects. Unlike the code in the ilatebinding pseudoexample, idispatch does not let you invoke a method by string name in a. Interfaceisdual public interface inet bool funcout object xml. Boolean values default to marshaling as a native 4byte win32 bool value as shown in the following example. The most serious of these problems is the performance of idispatchbased components.
Nov 02, 2011 setting a property by idispatch invoke. It also provides the information necessary to invoke these properties and methods. The following examples show how to access an activex or ole object through the idispatch interface. To identify methods, properties, and arguments, you use the dispatch identifier in the idispatchinvoke call. One caveat is that if you pass multiple parameters, they need to be passed in reverseorder. Aug 22, 2009 lets translate this real world example to technical terms. You use different idl attributes depending on whether you are implementing a pure idispatch interface or a dual interface. The dispatcher forwards one task after another to the server. The safearray and safearrayxxxx com runtime methods are.