Writing Object Properties
Services often contain child objects that belong to one of the formats that each service supports. For example, a Contacts service may support multiple contact objects of the Abstract Contact format. Each contact object is described by related properties (contact name, phone number, email address, and so on).
The WpdServicesApiSample application includes code that demonstrates how an application can update the name property for a child object of the given Contacts service. This sample uses the following WPD interfaces.
| Interface | Description |
|---|---|
| IPortableDeviceService | Used to retrieve the IPortableDeviceContent2 interface to access the supported service methods. |
| IPortableDeviceContent2 | Provides access to the content-specific methods. |
| IPortableDeviceProperties | Used to write the object property values and to determine whether a given property can be written |
| IPortableDeviceValues | Used to hold the property values to be written, determine results of the write operation, and retrieve attributes of properties (when determining write capability). |
When the user chooses option "8" at the command line, the application invokes the WriteContentProperties method that is found in the ContentProperties.cpp module. This method prompts the user to enter an object identifier for the property to be updated. The user identifies the object, and the method prompts the user to specify a new name. After this name is specified, the method updates the Name property for the given object.
Note that prior to writing the object properties, the sample application opens a Contacts service on a connected device.
The following code for the WriteContentProperties method demonstrates how the application uses the IPortableDeviceContent2 interface to retrieve an IPortableDeviceProperties interface. By passing the PROPERTYKEYS of the requested properties to the IPortableDeviceProperties::SetValues method, WriteContentProperties updates the name property.
void WriteContentProperties(
IPortableDeviceService* pService)
{
if (pService == NULL)
{
printf("! A NULL IPortableDeviceService interface pointer was received\n");
return;
}
HRESULT hr = S_OK;
WCHAR wszSelection[81] = {0};
WCHAR wszNewObjectName[81] = {0};
CComPtr<IPortableDeviceProperties> pProperties;
CComPtr<IPortableDeviceContent2> 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(wszSelection,sizeof(wszSelection));
if (FAILED(hr))
{
printf("An invalid object identifier was specified, aborting property reading\n");
}
// 1) Get an IPortableDeviceContent2 interface from the IPortableDeviceService interface to
// access the content-specific methods.
if (SUCCEEDED(hr))
{
hr = pService->Content(&pContent);
if (FAILED(hr))
{
printf("! Failed to get IPortableDeviceContent2 from IPortableDeviceService, hr = 0x%lx\n",hr);
}
}
// 2) Get an IPortableDeviceProperties interface from the IPortableDeviceContent2 interface
// to access the property-specific methods.
if (SUCCEEDED(hr))
{
hr = pContent->Properties(&pProperties);
if (FAILED(hr))
{
printf("! Failed to get IPortableDeviceProperties from IPortableDeviceContent2, hr = 0x%lx\n",hr);
}
}
// 3) Check the property attributes to see if we can write/change the NAME_GenericObj_Name property.
if (SUCCEEDED(hr))
{
hr = pProperties->GetPropertyAttributes(wszSelection,
PKEY_GenericObj_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 PKEY_GenericObj_Name reports TRUE\nThis means that the property can be changed/updated\n\n");
}
else
{
printf("The attribute WPD_PROPERTY_ATTRIBUTE_CAN_WRITE for PKEY_GenericObj_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 for PKEY_GenericObj_Name on object '%ws', hr = 0x%lx\n", wszSelection, hr);
}
}
}
// 4) Prompt the user for the new value of the NAME_GenericObj_Name property only if the property attributes report
// that it can be changed/updated.
if (bCanWrite)
{
printf("Enter the new PKEY_GenericObj_Name property for the object '%ws'.\n>",wszSelection);
hr = StringCbGetsW(wszNewObjectName,sizeof(wszNewObjectName));
if (FAILED(hr))
{
printf("An invalid PKEY_GenericObj_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_IPortableDeviceValues,
(VOID**) &pObjectPropertiesToWrite);
if (SUCCEEDED(hr))
{
if (pObjectPropertiesToWrite != NULL)
{
hr = pObjectPropertiesToWrite->SetStringValue(PKEY_GenericObj_Name, wszNewObjectName);
if (FAILED(hr))
{
printf("! Failed to add PKEY_GenericObj_Name to IPortableDeviceValues, hr= 0x%lx\n", hr);
}
}
}
}
// 6) Call SetValues() passing the collection of specified PROPERTYKEYs.
if (SUCCEEDED(hr))
{
hr = pProperties->SetValues(wszSelection, // 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", wszSelection, hr);
}
else
{
printf("The PKEY_GenericObj_Name property on object '%ws' was written successfully (Read the properties again to see the updated value)\n", wszSelection);
}
}
}
}
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