DispInvoker.exe is a self-extracting executable file that
provides functionality similar to the Visual Basic 6.0 CallByName function.
Most of the time you can discover the properties and methods of an object at
design-time and write code to handle them. In a few cases, however, you may not
know about an object's properties and methods in advance, or you may simply
want the flexibility of allowing an end user to specify properties or execute
methods at run-time. Visual Basic 6.0 introduced the CallByName function to
provide this functionality, but it is not available in earlier versions of
Visual Basic. The Dispinvoker sample provides similar functionality, allowing
you to create a wrapper object with:
- The same methods and properties of the original
object.
- An additional method, Call(), which allows calling methods
and retrieving properties from the original object by means of late binding.
Call() Method
- Contains the method or property name as the first
parameter.
- Receives the other method parameters as the subsequent
parameters.
- Returns the same value returned by the method or property
called.
The
following files are available for download from the Microsoft Download
Center:
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For
additional information about how to download Microsoft Support files, click the
following article number to view the article in the Microsoft Knowledge Base:
119591
(http://support.microsoft.com/kb/119591/EN-US/
)
How to Obtain Microsoft Support Files from Online Services
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| File Name | File Size |
|---|
| class1 | 1KB |
| DispTools.aps | 4KB |
| DispTools.clw | 1KB |
| DispTools.cpp | 4KB |
| DispTools.def | 1KB |
| DispTools.dll | 74KB |
| DispTools.dsp | 17KB |
| DispTools.dsw | 1KB |
| DispTools.h | 7KB |
| DispTools.idl | 1KB |
| DispTools.ncb | 153KB |
| DispTools.opt | 55KB |
| DispTools.plg | 4KB |
| DispTools.rc | 4KB |
| DispTools.tlb | 2KB |
| DispTools_i.c | 2KB |
| DispTools_p.c | 7KB |
| DispToolsps.def | 1KB |
| DispToolsps.mk | 1KB |
| dlldata.c | 1KB |
| dlldatax.c | 1KB |
| form1 | 3KB |
| lUnklmpl.cpp | 1KB |
| lUnklmpl.h | 1KB |
| lUnklmpl.rgs | 1KB |
| module1 | 1KB |
| Mssccprj | 1KB |
| Project1 | 22KB |
| Project1 | 1KB |
| resource.h | 1KB |
| StdAfx.cpp | 1KB |
| StdAfx.h | 1KB |
| Wrap.cpp | 2KB |
| Wrap.h | 5KB |
| Wrap.rgs | 1KB |
Automation allows calling objects in three ways:
- Vtable Binding: The method is referenced directly; the
compiler replaces the method call with an explicit reference to the method
code.
- Early Binding: The method is called by means of an ID
(DISPID).
- Late Binding: The method is called by name, the method ID
is retrieved at run-time.
Development tools, such as Visual Basic, allow limited use of
late binding. Method names must always be explicitly specified at design-time
and cannot be specified at run-time.
Dispinvoker is a C++ Dispatch
object that allows full exploitation of late binding.
An Automation
Object, obj, and the wrapper object, objWrap, may be obtained as follows:
Set objWrap = Wrap.GetInvoker(obj)
objWrap has the same methods as obj plus the additional method Call(),
which allows full use of late binding.
The Call() method in the
Dispinvoker wrapper uses the GetIDsOfNames() method to determine the DispID of
the method to be called. The call is then issued with the parameters passed
from the client.
Here are a few things to keep in mind:
- The Call method does not support named
parameters.
- The Call method does not allow you to assign values to
properties. They may only be read.
- The Dispinvoker wrapper does not return Type information
(GetTypeInfoCount method returns 0, GetTypeInfo method returns E_NOTIMPL)
- Dispinvoker uses DISPID_EVALUATE for the method
call.
Sample Code
Given a Visual Basic client and an automation object named obj,
of type Class1, with method mySub(), add the following code:
' Create an object of type class1
Dim obj As New Class1
Dim wrp as New DISPTOOLSLib.Wrap
Dim objWrp As Object
' Retrieve the DispInvoker wrapper
Set objWrp = wrp.GetInvoker(obj)
obj.mySub ' Calls method mySub directly on the object obj.
objWrp.mySub ' Calls method mySub on the DispInvoker wrapper ObjWrp.
objWrp.Call("mySub") ' Calls method mySub using Call() method on the
' DispInvoker wrapper.
'-------------------------------- Running the preceding code does the following:
- Creates the Automation object.
- Gets the DispInvoker Wrapper.
- Shows calling mySub method directly onto the object by
means of the Dispinvoker wrapper.
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