OleCreateEmbeddingHelper function (ole2.h)

Article
10/13/2021

Creates an OLE embedding helper object using application-supplied code aggregated with pieces of the OLE default object handler. This helper object can be created and used in a specific context and role, as determined by the caller.

Syntax

HRESULT OleCreateEmbeddingHelper(
  [in]  REFCLSID       clsid,
  [in]  LPUNKNOWN      pUnkOuter,
  [in]  DWORD          flags,
  [in]  LPCLASSFACTORY pCF,
  [in]  REFIID         riid,
  [out] LPVOID         *lplpObj
);

Parameters

[in] clsid

CLSID of the class to be helped.

[in] pUnkOuter

If the embedding helper is to be aggregated, pointer to the outer object's controlling IUnknown interface. If it is not to be aggregated, although this is rare, the value should be NULL.

[in] flags

DWORD containing flags that specify the role and creation context for the embedding helper. For legal values, see the following Remarks section.

[in] pCF

Pointer to the IClassFactory interface on the class object the function uses to create the secondary object. In some situations, this value may be NULL. For more information, see the following Remarks section.

[in] riid

Reference to the identifier of the interface desired by the caller.

[out] lplpObj

Address of pointer variable that receives the interface pointer requested in riid. Upon successful return, *ppvObj contains the requested interface pointer on the newly created embedding helper.

Return value

This function returns S_OK on success. Other possible values include the following.

Return code	Description
E_OUTOFMEMORY	Insufficient memory for the operation.
E_INVALIDARG	One or more parameters are invalid.
E_UNEXPECTED	An unexpected error has occurred.
E_NOINTERFACE	The provided interface identifier is invalid.

Remarks

The OleCreateEmbeddingHelper function creates an object that supports the same interface implementations found in the default handler, but which has additional hooks that allow it to be used more generally than just as a handler object. The following two calls produce the same result:

OleCreateEmbeddingHelper(clsid, pUnkOuter, EMBDHLP_INPROC_HANDLER | 
    EMBDHLP_CREATENOW, NULL, iid, ppvObj) 
 
OleCreateDefaultHandler(clsid, pUnkOuter, iid, ppvObj)

The embedding helper is aggregatable; pUnkOuter is the controlling IUnknown of the aggregate of which the embedding helper is to be a part. It is used to create a new instance of the OLE default handler, which can be used to support objects in various roles. The caller passes a pointer to its IClassFactory implementation to OleCreateEmbeddingHelper. This object and the default handler are then aggregated to create the new embedding helper object.

The OleCreateEmbeddingHelper function is usually used to support one of the following implementations:

An EXE object application that is being used as both a container and a server, and which supports inserting objects into itself. For this case, CreateEmbeddingHelper allows the object to support the interfaces usually supported only in the handler. To accomplish this, the application must first register its CLSID for different contexts, making two registration calls to the CoRegisterClassObject function, rather than one, as follows:
```
CoRegisterClassObject(clsidMe, pUnkCfLocal, CLSCTX_LOCAL_SERVER, 
        REGCLS_MULTI_SEPARATE...) 
 
    CoRegisterClassObject(clsidMe, pUnkCfInProc, CLSCTX_INPROC_SERVER, 
    
        REGCLS_MULTI_SEPARATE...) 
```
In these calls, you would pass along different class factory implementations to each of pUnkCfLocal and pUnkCfInProc. The class factory pointed to by pUnkCfLocal would be used to create objects that are to be embedded in a remote process, which is the normal case which uses a handler object associated with the client. However, when a server both creates an object and embeds it within itself, pUnkCfInProc points to a class object that can create an object that supports the handler interfaces. The local class is used to create the object and the in-process class creates the embedding helper, passing in the pointer to the first object's class factory in pCF.
A custom in-process object handler, in which case, the DLL creates the embedding helper by passing in a pointer to a private implementation of IClassFactory in pCF.

The flags parameter indicates how the embedding helper is to be used and how and when the embedding helper is initialized. The values for flags are obtained by OR-ing together values from the following table.

Values for flags Parameter	Purpose
EMBDHLP_INPROC_HANDLER	Creates an embedding helper that can be used with DLL object applications; specifically, the helper exposes the caching features of the default object handler.
EMBDHLP_INPROC_SERVER	Creates an embedding helper that is to be used as part of an in-process server. pCF cannot be NULL.
EMBDHLP_CREATENOW	Creates the secondary object using pCF immediately; if pCF is NULL, the standard proxy manager is used.
EMBDHLP_DELAYCREATE	Delays creation of the secondary object until it is needed (when the helper is put into the running state) to enhance speed and memory use. pCF must not be NULL. The EMBDHLP_INPROC_HANDLER flag cannot be used with this flag.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	ole2.h
Library	Ole32.lib
DLL	Ole32.dll
API set	ext-ms-win-com-ole32-l1-1-5 (introduced in Windows 10, version 10.0.15063)