IWMDMEnumStorage::Next

The Next method retrieves a pointer to the next sibling storage.

Syntax

HRESULT Next(ULONGcelt,IWMDMStorage**ppStorage,ULONG*pceltFetched);

Parameters

celt

[in]  Number of storages requested.

ppStorage

[out] Pointer to caller-allocated array of IWMDMStorage interface pointers. The size of this array must be IWMDMStorage*[celt]. The caller must release these interfaces when done with them. To avoid allocating a whole array, simply pass in the address of a pointer to an IWMDMStorage interface, as shown in Remarks.

pceltFetched

[out]  Number of storages enumerated.

Return Values

The method returns an HRESULT. All the interface methods in Windows Media Device Manager can return any of the following classes of error codes:

• Standard COM error codes
• Windows error codes converted to HRESULT values
• Windows Media Device Manager error codes

For an extenstive list of possible error codes, see Error Codes.

Possible values include, but are not limited to, those in the following table.

Remarks

Windows Media Device Manager delegates the storage enumeration to the corresponding service provider. For information on service provider storage enumeration, see the IMDSPEnumStorage interface.

The storage enumerator may not reflect the effect of media insertion and removal. In that case, the application should obtain a new storage enumerator object by calling IWMDMDevice::EnumStorage to get the refreshed list.If you only want to retrieve a single interface at a time, you do not need to allocate an array for this method, as shown in the following code.

Example Code

The following two C++ functions recursively explore a device. The first one is a kickoff functio that obtains the IWMDMEnumStorage interface of the root device storage. It passes this to the recursive function which examines all the nested functions.

// Kickoff function to explore a device.
void ExploreDevice(IWMDMDevice* pDevice)
{
    HRESULT hr = S_OK;

    // Get a root enumerator.
    CComPtr<IWMDMEnumStorage> pEnumStorage;
    hr = pDevice->EnumStorage(&pEnumStorage);
    RecursiveExploreStorage(pEnumStorage);

    HANDLE_HR(hr, "Got a root storage in ExploreDevice.","Couldn't get a root storage in ExploreDevice.");

e_Exit:
    return;
}

void RecursiveExploreStorage(IWMDMEnumStorage* pEnumStorage)
{
    HRESULT hr = S_OK;
    CComPtr<IWMDMStorage> pStorage;
    ULONG numRetrieved = 0;
    // Loop through all storages in the current storage.
    // We don't need to allocate an array to retrieve one 
    // interface at a time.
    while(pEnumStorage->Next(1, &pStorage, &numRetrieved) == S_OK && numRetrieved == 1)
    {
        // Get the name of the object. The first time this is called on a 
        // device, it will retrieve '\' as the root folder name.
        const UINT MAX_LEN = 255;
        WCHAR name[MAX_LEN];
        hr = pStorage->GetName((LPWSTR)&name, MAX_LEN);
        // TODO: Display the storage name.

    
        // Get metadata for the storage.
        if (SUCCEEDED(hr))
            GetMetadata(pStorage);

        // Find out something about the item.
        DWORD attributes = 0;
        _WAVEFORMATEX audioFormat;
        hr = pStorage->GetAttributes(&attributes, &audioFormat);
        HANDLE_HR(hr, "Got storage attributes in RecursivelyExploreStorage.","Couldn't get storage attributes in RecursivelyExploreStorage.");

        // If this is a folder, recurse into it.
        if (attributes & WMDM_FILE_ATTR_FILE)
            // TODO: Display a message indicating that this is a file.
        if (attributes & WMDM_FILE_ATTR_FOLDER)
        {
            // TODO: Display a message indicating that this is a folder.
            CComPtr<IWMDMEnumStorage> pEnumSubStorage;
            hr = pStorage->EnumStorage(&pEnumSubStorage);
            RecursiveExploreStorage(pEnumSubStorage);
        }

        // Some other useful attributes to check include:
        // WMDM_FILE_ATTR_CANDELETE and WMDM_FILE_ATTR_CANPLAY and others to determine what can be done with a storage.
        // WMDM_FILE_ATTR_HIDDEN and other attributes to determine display characteristics,
        // WMDM_STORAGE_IS_DEFAULT to see if this is the default save location for new files.
        pStorage.Release();
    } // Get the next storage pointer.

e_Exit:
    return;
}

Requirements

Header: Defined in mswmdm.h.

Library: mssachlp.lib

See Also

• Exploring a Device
• IWMDMDevice::EnumStorage
• IWMDMEnumStorage Interface