How to implement invoke for idispatch visual basic. I can get the function to work on methods that do not accept any parameters i. Extending iunknown, it is one of the standard interfaces that can be exposed by com objects. Calling idispatchgetidsofnames for functions with one. This causes mshtml to call idispatch invoke on the host application, passing along the same dispid. In atl, idispatchinvoke is implemented by idispatchimpl. Each method of the outgoing interface represents a single event or request. In fact, invoke is the only way to execute a userdefined method through the idispatch interface.
I am using the function idispatchgetidsofnames to get ids on methods and their parameters to then pass on to idispatchinvoke. Idispatchinvoke with atl microsofts tree view control. Generally, you should not implement invoke directly. Another option if you dont want to use mfc is to create a new project, import the type library, then copy and paste the idispatch invoke code from the generated functions into your code. Idispatch is the interface that exposes the ole automation protocol. Tobjectdispatchinvoke delphi rad studio code examples. But when i compile my sistem i have no idea of how script the user will use, and what functions he will create and what parameters this functions can have. Personsviewmodel is the client of ipersonrepository which is an interface representing the server.
The vtable of a dispinterface is identical to that of idispatch itself. I cant use ireflect interface here due to design issues, i need to handle getidsofnames and invoke manually. Idispatch doesnt offer any functionality of its own. An idispatch implementation can associate any positive integer id value with a given name. You may, however, go beyond just handling windows event and create. In essence, idispatch represents a standard vtable with a highly extensible invocation architecture. Jan 11, 2015 hence the discussion that follow will work only for idispatch based objects. I think i could have found another problem with the atl generated code for idispatchinvoke. As you can see, idispatch is a single physical interface that allows less sophisticated clients to get at any number of logical interfaces. Activex or ole objects can implement the idispatch interface for access by activex clients, such as visual basic. The dispids that identify members are defined by the implementor of the object and can be determined by using the objects documentation, the idispatch getidsofnames function, or the itypeinfo interface. The class here comprises simply of string property name, a numerical property value and a method square for returning the square of value. Getting the functions and parameters list from a idispatch.
Their implementations of invoke are inconsistent and difficult to read, mixing windowsspecific interface code with plugin behavior cleaning up this code is related to eliminating atl, as the classes atlccombstr and atlccomvariant have both been used in the interface code. The dispidmember argument identifies the member to invoke. Flags describing the context of the call to idispatch invoke. As a consequence, it must implement idispatch and therefore iunknown. The control container, internet explorer in this case, connects an idispatch implementation to the appropriate point. Supporting automation events in delphi delphi programming. This should remove any dependancy on mfc and give you the correct calling syntax. This causes mshtml to call idispatchinvoke on the host application, passing along the same dispid. Cmultidispatch multiple idispatch interfaces for automation clients. Then i call the getidsofnamesinvoke function of idispatch to execute the function. You can rate examples to help us improve the quality of examples. If you are going to use the idispatch interfaces rather than generate headers using the midl compiler, i suggest you wrap the calls to invoke and getidsofnames into wrapper functions.
In a real life scenario, you can imagine creating a sqlpersonrepository. Automation objects supply services to their clients by letting them invoke methods of. Reflection with idispatchbased com objects codeproject. This idispatch can be used to call any function on the script. Hence the discussion that follow will work only for idispatchbased objects. The identifier uniquely identifies a method, a property, and a list of parameters to be passed to the called.
I believe you can still access the methods using reflection\ invoke. The central idispatch method is idispatch invoke, which a client calls to invoke a particular method in the component. A class that acts as an automation controller is defined tmyclass with a method that takes no arguments and returns an integer mymethod. Idispatchinvoke passes me disp parameters in reverse. For example, if an automation method expects a reference to a doubleprecision number as an parameter, but receives a reference to an integer, the parameter is coerced. Atl generated code for idispatch invoke method is incorrect. The methods and properties of the dispinterface are accessible only via the idispatch invoke method. Invoke requires a previously obtained dispatch identifier. The following is a sample idl definition for such a com class. I believe you can still access the methods using reflection\invoke. Cmultidispatchgetidsofnames simply walks the static array calling getidsofnames until successful hence one of the limitations. Generally, calls to idispatch invoke are preceeded by calls to idispatch getidsofnames. Com programming idispatch, queryinterface, cocreateinstance, iunknown, gettickcount, itoa, atl control. I think vb 5 supports iuknown but vb 4 supports only idispatch.
In com, every interface method must return an error code to the client. 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. There are many examples of how to call idispatchinvoke with a bstr parameter. Jul, 2004 for example, if an automation method expects a reference to a doubleprecision number as an parameter, but receives a reference to an integer, the parameter is coerced. This page was last modified on 28 march 2012, at 19. Jan 07, 20 idispatchinfo omits the fourth idispatch method i. We have two functions in the plugin code that implement idispatch, cpluginusersettings and cpluginclass. Then the client can directly invoke methods of the com object through the. The mfc library steps in on both sides of the invoke call, using a datadriven scheme to call component functions based on dispatch map parameters that you define with. From what i understand, idispatch and invoke are used to support late bound clients. Implementing the idispatch interface microsoft docs. Another option if you dont want to use mfc is to create a new project, import the type library, then copy and paste the idispatchinvoke code from the generated functions into your code.
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. To better understand how the idispatch interface works, it is helpful to think of it as a kind of surrogate interface. For a list of possible values, see the wflags parameter in idispatch invoke in the windows sdk. The simplest use of invoke is to call a method that does not have any. Zero is reserved for the default, or value property. I successfully connect the iwebbrowser2 interface to a dwebbrowserevents2 dispatch event, and my idispatchinvoke is called successfully when a user clicks an url. Invoking javascript callbacks using com automation dr dobbs. To signal an event, the control calls idispatchinvoke through that connection. The v table of a dispinterface is identical to that of idispatch itself. Interfaces by convention all have a prefix letter of i, for example imalloc, istream and idispatch. The idispatch interface inherits from the iunknown interface. Obtain type information of idispatchbased com objects. Instead, use the dispatch interface to create functions createstddispatch and dispinvoke.
Guid0002040000000000c000000000000046 interfacetypecominterfacetype. 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. I am using html in my app and i am trying to capture clicks from the user. The dispid is returned to the client and the structures boolean entry was set to true. All i had to do was to find the correct idispatchimpl portion of the vtable to pass to the ccomtypeinfoholderinvoke method. An interface based solely on idispatch is called a dispinterface. For details, refer to createstddispatch, dispinvoke, creating the idispatch interface and exposing activex objects if some applicationspecific processing needs to be performed before calling a member, the code should perform the necessary. When one client is finished with an interface, it should call its release method to decrement the reference count.
You use different idl attributes depending on whether you are implementing a pure idispatch interface or a dual interface. Note that the invocation is done with the help of a dispid dispatch identifier obtained with the getidsofnames. Internet explorer then routes the call to the script handler block, based on the events source and name. 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. I am using the function idispatch getidsofnames to get ids on methods and their parameters to then pass on to idispatch invoke. For a list of possible values, see the wflags parameter in idispatchinvoke in the windows sdk. Since an interface describes available behaviour in an object, such a class or struct will have the pure. Generally, calls to idispatchinvoke are preceeded by calls to idispatchgetidsofnames. 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. The objects properties and methods can be accessed using idispatch getidsofnames and idispatch invoke the following examples show how to access an activex or ole object through the idispatch. The client queries the object using idispatch methods, and then executes the method via invoke. The central idispatch method is idispatchinvoke, which a client calls to invoke a particular method in the component. Aug 14, 2002 invoke method of the site that sets these flags.
A dual interface is an idispatch based interface that also has vtable entries for the methods in the custom interface. Flags describing the context of the call to idispatchinvoke. I used the wizard to create a single object with the atl wizards, added some method to its idispatchgenerated interface and let the attribute provider generate the idispatch code. The attribute dual indicates the methods may be called either directly using early binding, or indirectly using late binding using idispatch invoke. Resume next resume normal execution at next line of throw point. I successfully connect the iwebbrowser2 interface to a dwebbrowserevents2 dispatch event, and my idispatch invoke is called successfully when a user clicks an url. The article understanding com event handling by lim bio liong on the code. There are many examples of how to call idispatch invoke with a bstr parameter.
35 1223 628 1495 382 931 1185 43 1115 1081 109 1255 1042 1535 1454 1077 1100 561 1049 1437 658 1325 235 745 243 376 1350 545 1065 1090 917 200 283 1152 172 295 764