Contoh kode untuk membaca properti perangkat

Contoh kode berikut menunjukkan cara membaca properti perangkat dari Penyimpanan Properti. Untuk contoh cara membuka Penyimpanan Properti untuk objek Instans Fungsi saat ini, lihat Contoh Kode untuk Membuka Penyimpanan Properti.

/**************************************************************************\
* CWSDDevice::ReadDeviceProperty
*
* Reads a LPWTSR device property from the device metadata and returns 
* a copy of its value as a BSTR character string. 
*
*
* Arguments:
*
*    pPropertyStore        - IPropertyStore interface, optional
*                            (if not specified a new property store
*                            Is opened and closed for each call)
*    pPropertyKey          - property key (for example, PKEY_PNPX_FirmwareVersion)
*    pbstrPropertyValue    - Returns the property value; this value must be 
*                            freed by caller using SysFreeString
*
* Return Value:
*
*     S_OK if operation is successful, an error HRESULT otherwise
*
\**************************************************************************/

HRESULT
CWSDDevice::ReadDeviceProperty(
    __in_opt IPropertyStore *pPropertyStore,
    __in const PROPERTYKEY  *pPropertyKey,
    __out BSTR              *pbstrPropertyValue)
{
    HRESULT hr = S_OK;
    IPropertyStore *pThisPropertyStore = NULL;
    BOOL bClosePropertyStore = FALSE;
    PROPVARIANT propvar = {0};

    if ((!pbstrPropertyValue) || (!pPropertyKey))
    {
        hr = E_INVALIDARG;
        WIAS_ERROR((g_hInst, "Invalid argument, hr = 0x%08X", hr));
    }

    if ((!m_pFunctionInstance) || (!m_pScanProxy))
    {
        hr = E_UNEXPECTED;
        WIAS_ERROR((g_hInst, "ScanProxy not initialized, hr = 0x%08X", hr));
    }

    if (SUCCEEDED(hr))
    {
        pThisPropertyStore = pPropertyStore;
 
        if (!pThisPropertyStore)
        {
            hr = m_pFunctionInstance->OpenPropertyStore(STGM_READ, &pThisPropertyStore);
            if ((SUCCEEDED(hr)) && (!pThisPropertyStore))
            {
                hr = E_POINTER;
                WIAS_ERROR((g_hInst, 
                    "IFunctionInstance::OpenPropertyStore returned hr = 0x%08X with a NULL property store interface, hr = 0x%08X", hr));
            }
            if (FAILED(hr))
            {
                WIAS_ERROR((g_hInst, "IFunctionInstance::OpenPropertyStore failed, hr = 0x%08X", hr));
            }

            if (pThisPropertyStore)
            {
                bClosePropertyStore = TRUE;
            }
        }    
    }
 
    PropVariantInit(&propvar);

    if (SUCCEEDED (hr))
    {
        hr = pThisPropertyStore->GetValue(*pPropertyKey, &propvar);
        if (FAILED(hr))
        {
            WIAS_ERROR((g_hInst, "IPropertyStore::GetValue failed, hr = 0x%08X", hr));
        }
    }

    if ((SUCCEEDED(hr)) && (VT_EMPTY == propvar.vt))
    {
        hr = E_FAIL;
        WIAS_ERROR((g_hInst, "IPropertyStore::GetValue returned no value (VT_EMPTY), hr = 0x%08X", hr));
    }

    if ((SUCCEEDED(hr)) && (VT_LPWSTR != propvar.vt))
    {
        hr = E_UNEXPECTED;
        WIAS_ERROR((g_hInst, "IPropertyStore::GetValue returned an unexpected PROPVARIANT type, hr = 0x%08X", hr));
    }

    if (SUCCEEDED (hr))
    {
        *pbstrPropertyValue = SysAllocString(propvar.pwszVal);
        if (!(*pbstrPropertyValue))
        {
            hr = E_OUTOFMEMORY;
            WIAS_ERROR((g_hInst, 
                "Cannot make a copy of the value returned by IPropertyStore::GetValue, %ws, hr = 0x%08X", propvar.pwszVal, hr));
        }
    }

    PropVariantClear(&propvar);

    if ((bClosePropertyStore) && (pThisPropertyStore))
    {
        pThisPropertyStore->Release();
        pThisPropertyStore = NULL;
    }

    return hr;
}