次の方法で共有

IWMDMDevice3::GetProperty

  • [アーティクル]
banner art

The GetProperty method retrieves a specific device metadata property.

Syntax

HRESULT GetProperty(LPCWSTRpwszPropName,PROPVARIANT*pValue);

Parameters

pwszPropName

[in]  A wide character, null-terminated string name of the property to retrieve. A list of standard property name constants is given in Metadata Constants.

pValue

[out]  Returned value for the property. The application must free this memory using PropVariantClear.

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.
E_INVALIDARG One or both parameters are NULL.
WMDM_E_NOTSUPPORTED The property is not supported by the device or the device returned an error.

Remarks

To obtain the list of supported device properties, the client call this function and specify g_wszWMDMSupportedDeviceProperties. For the list of standard device property names, see Metadata Constants.

The client should pass in a pointer to an empty PROPVARIANT in the pValue parameter. On return, pValue will contain the value of the property.

This method is similar to the GetMetadata and GetSpecifiedMetadata methods for storages, but this method can get only one property at a time.

Sample Code

The following C++ code queries for the g_wszWMDMFormatsSupported property, which returns a SAFEARRAY list of formats supported by a device.

// Query a device for supported configurations for each media or format type. 
HRESULT GetCaps(IWMDMDevice3* pDevice)
{
    HRESULT hr = S_OK;

    // Request the "formats supported" property to get a list of supported formats.
    PROPVARIANT pvFormatsSupported;
    PropVariantInit(&pvFormatsSupported);
    hr = pDevice->GetProperty(g_wszWMDMFormatsSupported, &pvFormatsSupported);
    HANDLE_HR(hr, "Got a property list in GetCaps", "Couldn't get a property list in GetCaps.");

    // Loop through the retrieved format list.
    // For each format, get a list of format configurations.
    SAFEARRAY* formatList = pvFormatsSupported.parray;
    WMDM_FORMATCODE formatCode = WMDM_FORMATCODE_NOTUSED;
    for(LONG iCap = 0; iCap < formatList->rgsabound[0].cElements; iCap++)
    { 
        // Get a format from the SAFEARRAY of retrieved formats.
        SafeArrayGetElement(formatList, &iCap, &formatCode);

        // Call a custom function to see the specifics of device support for 
       // each format.
        if (formatCode != WMDM_FORMATCODE_NOTUSED)
            myGetFormatCaps(formatCode, pDevice);
    }

e_Exit:
    // Clear out the memory we used.
    PropVariantClear(&pvFormatsSupported);
    return hr;
}

Requirements

Header: Defined in mswmdm.h.

Library: mssachlp.lib

See Also