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IWMDMEnumDevice::Next

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The Next method returns a pointer to the next device, represented by an IWMDMDevice interface.

Syntax

HRESULT Next(ULONGcelt,IWMDMDevice**ppDevice,ULONG*pceltFetched);

Parameters

celt

[in]  Number of devices requested.

ppDevice

[out]  Pointer to caller-allocated array of IWMDMDevice interface pointers. The size of this array must be IWMDMDevice*[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 IWMDMDevice interface, as shown in Remarks.

pceltFetched

[out]  Pointer to a variable that receives the number of devices (interfaces) returned.

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.

Return code Description
S_OK The method succeeded.
S_FALSE Fewer than celt devices were retrieved.
E_FAIL An unspecified error occurred.

Remarks

The returned device interface(s) are based on a cached list of devices. If a Plug and Play device is attached or removed, the current enumerator will not reflect that, and therefore, Next will return devices based on the cached list. Applications should obtain a new enumerator object by calling IWMDeviceManager::EnumDevices to get a refreshed list of devices.

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:

// Get a device enumerator to examine each device.
CComPtr<IWMDeviceManager2> pIWMDevMgr2;
hr = m_IWMDeviceMgr->QueryInterface (__uuidof(IWMDeviceManager2), (void**) &pIWMDevMgr2);
if (hr == S_OK)
{
    // TODO: Display a message that the application retrieved IWMDeviceManager2.
}
else
{
    // TODO: Display a message that the application was not able to 
    // retrieve IWMDeviceManager2 in EnumDevices.
    return hr;
}

// Enumerate through the devices using the faster EnumDevices2 plug-and-play method.
CComPtr<IWMDMEnumDevice> pEnumDevice;
hr = pIWMDevMgr2->EnumDevices2(&pEnumDevice);
if (hr != S_OK)
{
    //.TODO: Display a message that an error occurred in calling EnumDevices2.
    return hr;
}

// Enumerate through devices.
IWMDMDevice *pIWMDMDevice;
ULONG ulFetched = 0;
while(pEnumDevice->Next(1, &pIWMDMDevice, &ulFetched) == S_OK)
{
    if (ulFetched != 1)
    {
        return E_FAIL;
    }
    // Do some stuff here....
}

Requirements

Header: Defined in mswmdm.h.

Library: mssachlp.lib

See Also