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IEnumPortableDeviceObjectIDs::Next

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IEnumPortableDeviceObjectIDs::Next

The Next method retrieves the next one or more object IDs in the enumeration sequence.

Syntax

  HRESULT Next(
  ULONG  cObjects,
  LPWSTR*  pObjIDs,
  ULONG*  pcFetched
);

Parameters

cObjects

[in]  A count of the objects requested.

pObjIDs

[in, out]  An array of LPWSTR pointers, each specifying a retrieved object ID. The caller must allocate an array of cObjects LPWSTR elements. The caller must free both the array and the returned strings. The strings are freed by calling CoTaskMemFree.

pcFetched

[in, out]  On input, the number of IDs to retrieve. On output, the number of IDs actually retrieved. If no object IDs are released and the return value is S_FALSE, there are no more objects to enumerate.

Return Values

The method returns an HRESULT. Possible values include, but are not limited to, those in the following table.

Return code Description
S_OK The method succeeded.
S_FALSE There are no more objects to enumerate.

Remarks

If fewer than the requested number of elements remain in the sequence, this method retrieves the remaining elements. The number of elements that are actually retrieved is returned through pcFetched (unless the caller passed in NULL for that parameter). Enumerated objects are all peers—that is, enumerating children of an object will enumerate only direct children, not grandchild or deeper objects.

Example Code

// This number controls how many object identifiers are requested during each call
// to IEnumPortableDeviceObjectIDs::Next()
#define NUM_OBJECTS_TO_REQUEST  10

// Recursively called function which enumerates using the specified
// object identifier as the parent.
void RecursiveEnumerate(LPCWSTR wszParentObjectID, IPortableDeviceContent* pContent)
{
    HRESULT                       hr             = S_OK;
    IEnumPortableDeviceObjectIDs* pEnumObjectIDs = NULL;

    if ((wszParentObjectID == NULL) ||
        (pContent          == NULL))
    {
        return;
    }

    // wszParentObjectID is the object identifier of the parent being used for enumeration

    // Get an IEnumPortableDeviceObjectIDs interface by calling EnumObjects with the
    // specified parent object identifier.
    hr = pContent->EnumObjects(0, wszParentObjectID, NULL, &pEnumObjectIDs);
    if (FAILED(hr))
    {
        // Failed to get IEnumPortableDeviceObjectIDs from IPortableDeviceContent
    }

    // Loop calling Next() while S_OK is being returned.
    while(hr == S_OK)
    {
        DWORD  cFetched = 0;
        LPWSTR szObjectIDArray[NUM_OBJECTS_TO_REQUEST] = {0};
        hr = pEnumObjectIDs->Next(NUM_OBJECTS_TO_REQUEST, // Number of objects to request on each NEXT call
                                  szObjectIDArray,        // Array of LPWSTR array which will be populated on each NEXT call
                                  &cFetched);             // Number of objects written to the LPWSTR array
        if (SUCCEEDED(hr))
        {
            // Traverse the results of the Next() operation and recursively enumerate
            // Remember to free all returned object identifiers using CoTaskMemFree()
            for (DWORD dwIndex = 0; dwIndex < cFetched; dwIndex++)
            {
                RecursiveEnumerate(szObjectIDArray[dwIndex],pContent);

                // Free allocated LPWSTRs after the recursive enumeration call has completed.
                CoTaskMemFree(szObjectIDArray[dwIndex]);
                szObjectIDArray[dwIndex] = NULL;
            }
        }
    }

    // Release the IEnumPortableDeviceObjectIDs when finished
    if (pEnumObjectIDs != NULL)
    {
        pEnumObjectIDs->Release();
        pEnumObjectIDs = NULL;
    }
}

Requirements

Header: Defined in PortableDeviceApi.h

Library: PortableDeviceGUIDs.lib

See Also

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