A technical article found on the Microsoft Developer
Network CD-ROM titled "Implementing OLE Automation Collections," describes the
functionality necessary to create an OLE automation collection. This includes
creating a method called Item that returns the dispatch interface of the
indicated item in the collection.
All OLE automation collection
objects must implement the Item method to iterate through the objects of the
collection. The implementation of the method might have been created hidden in
the .ODL file for some applications. You cannot find these hidden methods by
calling IDispatch::GetIdsOfNames(). However, in many situations, this hidden
method is the default method of the collection, in which case you can invoke it
with an dispatch ID of DISPID_VALUE.
Visual Basic 3.0 depends on this
Item method being the default method of the collection object.
Back to the top
The following code sample illustrates using
COleDispatchDriver::InvokeHelper() to call the Item method from the Resources
collection class provided by Microsoft Project 4.1. The Item method is hidden
and cannot be found in the type library of the object:
Back to the top
Sample Code
void IterateCollection(void)
{
Application App; // wrapper class for the 'Application' object
Project Proj; // wrapper class for the 'Project' object
Resources Res; // wrapper class for the 'Resources' object
CString lpszFileName ("c:\\temp\\project2.mpp");
App.CreateDispatch("MSProject.Application");
VARIANT vFileName;
VariantInit(&vFileName);
V_VT(&vFileName) = VT_BSTR;
V_BSTR(&vFileName) = lpszFileName.AllocSysString();
App.FileOpen(vFileName);
Proj.AttachDispatch(App.GetActiveProject());
Res.AttachDispatch(Proj.GetResources());
VARIANT vCount;
VariantInit(&vCount);
V_VT(&vCount) = VT_I4;
vCount = Res.Count();
// the index of the collection starts with 1, not 0
for (int i = 1 ; i <= vCount.lVal ; i++)
{
Resource r; // wrapper class for the 'Resource' object
VARIANT vResult, vIndex, vStr;
VariantInit(&vResult);
VariantInit(&vIndex);
V_VT(&vIndex) = VT_I2;
V_I2(&vIndex) = i;
static BYTE parms[] = VTS_VARIANT;
Res.InvokeHelper(DISPID_VALUE, DISPATCH_METHOD, VT_VARIANT,
(void*)&vResult, parms, &vIndex);
r.AttachDispatch(vResult.pdispVal);
vStr = r.GetName();
// ... 'vStr' now contains the Name property
}
}
Back to the top
