HOWTO: Enumerate OLE and VB Controls from an OLE Control
ID: Q141414
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The information in this article applies to:
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Standard and Professional Editions of Microsoft Visual Basic programming system for Windows, versions 4.0, 5.0, 6.0
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Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 2.2, 4.0, 5.0, 6.0
SUMMARY
For an OLE control to communicate with another control placed on the same
Visual Basic form, the OLE control needs access to at least one interface
pointer of the other control. This article illustrates a technique you can
use to enumerate both OLE and Visual Basic controls present on a particular
form and retrieve an interface pointer to these controls. Note that the
same technique could be applied to enumerate controls placed on other
control containers, provided that container exposes the functionality
required to implement the technique.
MORE INFORMATION
Given a pointer to IOleClientSite, it is possible to enumerate through all
of the other controls on a form by making use of the following interfaces:
IOleClientSite
IOleContainer
IEnumUnknown
IUnknown
IOleObject
IOleClientSite
IOleControlSite
Note that most of these interfaces are container-side interfaces, so the
technique mentioned here is container dependent. For this method to work,
the container must provide support for IOleContainer, which is currently
defined as a mandatory interface in the OLE control container guidelines.
Both MFC version 4.0 and greater and Visual Basic version 4.0 and greater
OLE control containers provide support for this interface. Before using
this method with another control container, ensure that it provides support
for IOleContainer.
The method itself is illustrated by the sample code listed in this article.
You can incorporate the code into an OLE control generated using
ControlWizard. Use the code to enumerate all the controls, internal Visual
Basic controls as well OLE controls, by calling IOleContainer::EnumObjects,
and passing the following flags as its first parameter:
OLECONTF_EMBEDDINGS: is used to retrieve OLE Controls.
OLECONTF_OTHERS : is used to retrieve other objects such as Visual
Basic internal controls.
hr = lpContainer->EnumObjects(OLECONTF_EMBEDDINGS | OLECONTF_OTHERS,
&lpEnumUnk);
The differentiating aspect between OLE controls and other objects such as
internal Visual Basic controls is that only OLE controls support the
IOleObject interface. Hence, if a QueryInterface for IID_IOleObject fails
for an object, then it is a different type of object. Also, if the control
container provides support for Extended controls as does Visual Basic 4.0,
the Extended control for a particular OLE control can also be retrieved
using the method illustrated by the sample code.
Note that most of the functionality provided by the following sample code
depends solely on the extent of the functionality exposed by the control
container itself.
Also note that the LPOLECLIENTSITE pointer can be obtained through
a call to COleControl::GetClientSite().
Sample Code
void EnumAllControlNames(LPOLECLIENTSITE lpSite)
{
LPOLECONTAINER lpContainer;
LPENUMUNKNOWN lpEnumUnk;
// Note that the IOleContainer interface is currently defined as
// mandatory. It must be implemented by control containers,
// in the OLE Control Containers Guidelines.
HRESULT hr = lpSite->GetContainer(&lpContainer);
if(FAILED(hr)) {
OutputDebugString(_T("Unable to get to the container.\n"));
return;
}
// OLECONTF_EMBEDDINGS is used to retrieve OLE Controls.
// OLECONTF_OTHERS is used to retrieve other objects such as
// Visual Basic internal controls
hr = lpContainer->EnumObjects(
OLECONTF_EMBEDDINGS | OLECONTF_OTHERS,
&lpEnumUnk);
if(FAILED(hr)) {
lpContainer->Release();
return;
}
LPUNKNOWN lpUnk;
while (lpEnumUnk->Next(1, &lpUnk, NULL) == S_OK) {
LPOLEOBJECT lpObject = NULL;
LPOLECONTROLSITE lpTargetSite = NULL;
LPOLECLIENTSITE lpClientSite = NULL;
LPDISPATCH lpDisp;
hr = lpUnk->QueryInterface(
IID_IOleObject, (LPVOID*)&lpObject);
if(SUCCEEDED(hr)) {
// This is an OLE control.
// Navigate to the Extended Control because Visual Basic 4.0 uses
// Extended controls.
hr = lpObject->GetClientSite(&lpClientSite);
if(SUCCEEDED(hr)) {
// You have the IOleClientSite interface
hr = lpClientSite->QueryInterface(
IID_IOleControlSite, (LPVOID*)&lpTargetSite);
if(SUCCEEDED(hr)) {
// You have the IOleControlSite interface
// Get the IDispatch for the extended control.
// Note that Extended controls are optional in the OLE
// specifications for OLE Control Containers.
hr = lpTargetSite->GetExtendedControl(&lpDisp);
}
}
}
else {
// This is either an internal VB control or the
// VB form itself.
hr = lpUnk->QueryInterface(
IID_IDispatch, (LPVOID*)&lpDisp);
}
if(SUCCEEDED(hr)) {
VARIANT va;
VariantInit(&va);
DISPID dispid;
DISPPARAMS dispParams = { NULL, NULL, 0, 0 };
// Get the names of all the controls present in a VB form.
LPWSTR lpName[1] = { (WCHAR *)L"Name" };
hr = lpDisp->GetIDsOfNames(IID_NULL, lpName, 1,
LOCALE_SYSTEM_DEFAULT, &dispid);
if(SUCCEEDED(hr)) {
hr = lpDisp->Invoke(dispid/*0x80010000*/, IID_NULL,
LOCALE_SYSTEM_DEFAULT,
DISPATCH_PROPERTYGET |
DISPATCH_METHOD,
&dispParams, &va, NULL, NULL);
if(SUCCEEDED(hr)) {
CString szTmp((LPCWSTR)va.bstrVal);
// szTmp now has the name.
OutputDebugString(_T("And the name is ... ") + szTmp +
_T("\n"));
}
}
lpDisp->Release();
}
// Release interface pointers.
if(lpObject) lpObject->Release();
if(lpTargetSite) lpTargetSite->Release();
if(lpClientSite) lpClientSite->Release();
lpUnk->Release();
} // End of While statement
// Final clean up
lpEnumUnk->Release();
lpContainer->Release();
}
Additional words: VB VC visualc cdk ocx
Keywords : kbole kbCtrl kbMFC kbVC200 kbVC210 kbVC220 kbVC400 kbVC500 kbVC600 kbocx
Version : Winnet:2.0,2.1,2.2,4.0,5.0,6.0
Platform : NT WINDOWS
Issue type : kbhowto
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