Setting Properties for a Single Object

After your application retrieves an object identifier (see the Enumerating Content topic) for a given object, it can set properties for that object by calling methods in the interfaces described in the following table.

Interface Description
IPortableDeviceProperties Interface Used to determine whether a given property can be written and to send the write operation.
IPortableDeviceContent Interface Provides access to the content-specific methods.
IPortableDeviceValues Interface Used to hold the values to be written, determine results of the write operation, and retrieve attributes of properties (when determining write capability).

 

Applications set properties on an object by first creating a property bag that specifies the new values using the IPortableDeviceValues interface. Once the property bag is created, an application sets those properties by calling the IPortableDeviceProperties::SetValues method.

The WriteContentProperties function in the sample application's ContentProperties.cpp module demonstrates how an application could set a new object-name property for a selected object.

The first task accomplished by the WriteContentProperties function is to prompt the user to enter an object identifier for the object that the application will write the new name for.


HRESULT                               hr                   = S_OK;
WCHAR                                 szSelection[81]      = {0};
WCHAR                                 szNewObjectName[81]  = {0};
CComPtr<IPortableDeviceProperties>    pProperties;
CComPtr<IPortableDeviceContent>       pContent;
CComPtr<IPortableDeviceValues>        pObjectPropertiesToWrite;
CComPtr<IPortableDeviceValues>        pPropertyWriteResults;
CComPtr<IPortableDeviceValues>        pAttributes;
BOOL                                  bCanWrite            = FALSE;

// Prompt user to enter an object identifier on the device to write properties on.
printf("Enter the identifer of the object you wish to write properties on.\n>");
hr = StringCbGetsW(szSelection,sizeof(szSelection));
if (FAILED(hr))
{
    printf("An invalid object identifier was specified, aborting property reading\n");
}


After this, the application retrieves the WPD_PROPERTY_ATTRIBUTE_CAN_WRITE value for the WPD_OBJECT_NAME property to determine whether the property can be written. (Note that your application could set any property for which the WPD_PROPERTY_ATTRIBUTE_CAN_WRITE value is true.)


if (SUCCEEDED(hr))
{
    hr = pDevice->Content(&pContent);
    if (FAILED(hr))
    {
        printf("! Failed to get IPortableDeviceContent from IPortableDevice, hr = 0x%lx\n",hr);
    }
}

// 2) Get an IPortableDeviceProperties interface from the IPortableDeviceContent interface
// to access the property-specific methods.
if (SUCCEEDED(hr))
{
    hr = pContent->Properties(&pProperties);
    if (FAILED(hr))
    {
        printf("! Failed to get IPortableDeviceProperties from IPortableDevice, hr = 0x%lx\n",hr);
    }
}

// 3) Check the property attributes to see if we can write/change the WPD_OBJECT_NAME property.
if (SUCCEEDED(hr))
{
    hr = pProperties->GetPropertyAttributes(szSelection,
                                            WPD_OBJECT_NAME,
                                            &pAttributes);
    if (SUCCEEDED(hr))
    {
        hr = pAttributes->GetBoolValue(WPD_PROPERTY_ATTRIBUTE_CAN_WRITE, &bCanWrite);
        if (SUCCEEDED(hr))
        {
            if (bCanWrite)
            {
                printf("The attribute WPD_PROPERTY_ATTRIBUTE_CAN_WRITE for the WPD_OBJECT_NAME reports TRUE\nThis means that the property can be changed/updated\n\n");
            }
            else
            {
                printf("The attribute WPD_PROPERTY_ATTRIBUTE_CAN_WRITE for the WPD_OBJECT_NAME reports FALSE\nThis means that the property cannot be changed/updated\n\n");
            }
        }
        else
        {
            printf("! Failed to get the WPD_PROPERTY_ATTRIBUTE_CAN_WRITE value from WPD_OBJECT_NAME on object '%ws', hr = 0x%lx\n",szSelection, hr);
        }
    }
}


The next step is to prompt the user for the new name string. (Note that the call to the IPortableDeviceValues::SetStringValue method merely creates the property bag; the actual property has not been written yet.)


if (bCanWrite)
{
    printf("Enter the new WPD_OBJECT_NAME for the object '%ws'.\n>",szSelection);
    hr = StringCbGetsW(szNewObjectName,sizeof(szNewObjectName));
    if (FAILED(hr))
    {
        printf("An invalid object name was specified, aborting property writing\n");
    }

    // 5) CoCreate an IPortableDeviceValues interface to hold the property values
    // we wish to write.
    if (SUCCEEDED(hr))
    {
        hr = CoCreateInstance(CLSID_PortableDeviceValues,
                              NULL,
                              CLSCTX_INPROC_SERVER,
                              IID_PPV_ARGS(&pObjectPropertiesToWrite));
        if (SUCCEEDED(hr))
        {
            if (pObjectPropertiesToWrite != NULL)
            {
                hr = pObjectPropertiesToWrite->SetStringValue(WPD_OBJECT_NAME, szNewObjectName);
                if (FAILED(hr))
                {
                    printf("! Failed to add WPD_OBJECT_NAME to IPortableDeviceValues, hr= 0x%lx\n", hr);
                }
            }
        }
    }


Finally, the new value, specified by the user, is applied to the object.


if (SUCCEEDED(hr))
{
    hr = pProperties->SetValues(szSelection,                // The object whose properties we are reading
                                pObjectPropertiesToWrite,   // The properties we want to read
                                &pPropertyWriteResults);    // Driver supplied property result values for the property read operation
    if (FAILED(hr))
    {
        printf("! Failed to set properties for object '%ws', hr= 0x%lx\n", szSelection, hr);
    }
    else
    {
        printf("The WPD_OBJECT_NAME property on object '%ws' was written successfully (Read the properties again to see the updated value)\n", szSelection);
    }
}


Related topics

IPortableDevice Interface
IPortableDeviceContent Interface
IPortableDeviceKeyCollection Interface
IPortableDeviceProperties Interface
IPortableDevicePropertiesBulk Interface
IPortableDevicePropVariantCollection Interface
Programming Guide

 

 

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