Invoking Service Methods

The WpdServicesApiSample application includes code that demonstrates how an application can invoke the methods supported by a given Contacts service synchronously.. This sample uses the following interfaces

Interface	Description
IPortableDeviceService	Used to retrieve the IPortableDeviceServiceMethods interface to invoke methods on a given service.
IPortableDeviceServiceMethods	Used to invoke a service method.
IPortableDeviceValues	Used to hold the outgoing method parameters, and the incoming method results. This can be NULL if the method does not require any parameters or return any results.

 

When the user chooses option "9" at the command line, the application invokes the InvokeMethods method that is found in the ServiceMethods.cpp module. Note that prior to invoking the methods, the sample application opens a Contacts service on a connected device.

Service methods encapsulate functionality that each service defines and implements. They are unique to each type of service and are represented by a GUID. For example, the Contacts service defines a BeginSync method that applications call to prepare the device for synchronizing Contact objects, and an EndSync method to notify the device that synchronization has completed. Applications execute a method by calling IPortableDeviceServiceMethods::Invoke.

Service methods should not be confused with WPD commands. WPD commands are part of the standard WPD Device Driver Interface (DDI), and are the mechanism for communication between a WPD application and the driver. Commands are predefined, grouped by categories, for example, WPD_CATEGORY_COMMON, and are represented by a PROPERTYKEY structure. An application sends commands to the device driver by calling IPortableDeviceService::SendCommand. For more information, see the Commands topic.

The InvokeMethods method invokes the IPortableDeviceService::Methods method to retrieve an IPortableDeviceServiceMethods interface. Using this interface, it invokes the BeginSync and EndSync methods by calling the IPortableDeviceServiceMethods::Invoke method. Each time it calls Invoke, the application supplies the REFGUID for the method that is invoked.

The following code uses the InvokeMethods method.

// Invoke methods on the Contacts Service.
// BeginSync and EndSync are methods defined by the FullEnumerationSync Device Service.
void InvokeMethods(IPortableDeviceService* pService)
{
    HRESULT hr = S_OK;
    CComPtr<IPortableDeviceServiceMethods> pMethods;

    if (pService == NULL)
    {
        printf("! A NULL IPortableDeviceService interface pointer was received\n");
        return;
    }

    // Get an IPortableDeviceServiceMethods interface from the IPortableDeviceService interface to
    // invoke methods.
    hr = pService->Methods(&pMethods);
    if (FAILED(hr))
    {
        printf("! Failed to get IPortableDeviceServiceMethods from IPortableDeviceService, hr = 0x%lx\n",hr);
    }

    // Invoke() the BeginSync method
    if (SUCCEEDED(hr))
    {
        // This method does not take any parameters or results, so we pass in NULL
        hr = pMethods->Invoke(METHOD_FullEnumSyncSvc_BeginSync, NULL, NULL);
        if (SUCCEEDED(hr))
        {
            printf("%ws called, hr = 0x%lx\n",NAME_FullEnumSyncSvc_BeginSync, hr);
        }
        else
        {
            printf("! Failed to invoke %ws, hr = 0x%lx\n",NAME_FullEnumSyncSvc_BeginSync, hr);
        }
    }

    // Invoke the EndSync method asynchronously
    if (SUCCEEDED(hr))
    {
        // This method does not take any parameters or results, so we pass in NULL
        hr = pMethods->Invoke(METHOD_FullEnumSyncSvc_EndSync, NULL, NULL);
        if (SUCCEEDED(hr))
        {
            printf("%ws called, hr = 0x%lx\n",NAME_FullEnumSyncSvc_EndSync, hr);
        }
        else
        {
            printf("! Failed to invoke %ws, hr = 0x%lx\n",NAME_FullEnumSyncSvc_EndSync, hr);
        } 
    }
}

Related topics

IPortableDeviceService

IPortableDeviceServiceMethods

WpdServicesApiSample