消息传送功能

消息传递函数 WpdBaseDriver：:D ispatchWpdMessage 处理将消息分发到相应的驱动程序组件。 如果之前已对 Windows 进行过编程，则可以将 DispatchWpdMessage 函数视为类似于基于 Windows 的应用程序的 WindowProc 函数。

WpdBaseDriver：:D ispatchWpdMessage 函数检查WPD_Command类别，以确定它应在何处发送给定消息。 然后，它将此消息传递到相应的组件， (驱动程序) 中找到的枚举、属性、资源或功能组件。

pParams 参数指向包含给定命令的反序列化参数的 IPortableDeviceValues 集合。

pResults 参数指向函数在处理给定命令后填充的 IPortableDeviceValues 的空集合。

示例驱动程序的以下摘录包含 WpdBaseDriver：:D ispatchWpdMessage 的代码。

HRESULT WpdBaseDriver::DispatchWpdMessage(IPortableDeviceValues* pParams,
                                          IPortableDeviceValues* pResults)
{

    HRESULT     hr                  = S_OK;
    GUID        guidCommandCategory = {0};
    DWORD       dwCommandID         = 0;
    PROPERTYKEY CommandKey          = WPD_PROPERTY_NULL;

    if (hr == S_OK)
    {
        hr = pParams->GetGuidValue(WPD_PROPERTY_COMMON_COMMAND_CATEGORY, &guidCommandCategory);
        CHECK_HR(hr, "Failed to get WPD_PROPERTY_COMMON_COMMAND_CATEGORY from input parameters");
    }

    if (hr == S_OK)
    {
        hr = pParams->GetUnsignedIntegerValue(WPD_PROPERTY_COMMON_COMMAND_ID, &dwCommandID);
        CHECK_HR(hr, "Failed to get WPD_PROPERTY_COMMON_COMMAND_ID from input parameters");
    }

    // If WPD_PROPERTY_COMMON_COMMAND_CATEGORY or WPD_PROPERTY_COMMON_COMMAND_ID could not be extracted
    // properly then we should return E_INVALIDARG to the client.
    if (FAILED(hr))
    {
        hr = E_INVALIDARG;
        CHECK_HR(hr, "Failed to get WPD_PROPERTY_COMMON_COMMAND_CATEGORY or WPD_PROPERTY_COMMON_COMMAND_ID from input parameters");
    }

    if (hr == S_OK)
    {
        CommandKey.fmtid = guidCommandCategory;
        CommandKey.pid   = dwCommandID;

        if (CommandKey.fmtid == WPD_CATEGORY_OBJECT_ENUMERATION)
        {
            hr = m_ObjectEnum.DispatchWpdMessage(CommandKey, pParams, pResults);
        }
        else if (CommandKey.fmtid == WPD_CATEGORY_OBJECT_PROPERTIES)
        {
            hr = m_ObjectProperties.DispatchWpdMessage(CommandKey, pParams, pResults);
        }
        else if (CommandKey.fmtid == WPD_CATEGORY_OBJECT_RESOURCES)
        {
            hr = m_ObjectResources.DispatchWpdMessage(CommandKey, pParams, pResults);
        }
        else if (CommandKey.fmtid == WPD_CATEGORY_CAPABILITIES)
        {
            hr = m_Capabilities.DispatchWpdMessage(CommandKey, pParams, pResults);
        }
        else if (IsEqualPropertyKey(CommandKey, WPD_COMMAND_COMMON_GET_OBJECT_IDS_FROM_PERSISTENT_UNIQUE_IDS))
        {
            hr = OnGetObjectIDsFromPersistentUniqueIDs(pParams, pResults);
        }
        else
        {
            hr = E_NOTIMPL;
            CHECK_HR(hr, "Unknown command %ws.%d received",CComBSTR(CommandKey.fmtid), CommandKey.pid);
        }
    }

    HRESULT hrTemp = pResults->SetErrorValue(WPD_PROPERTY_COMMON_HRESULT, hr);
    CHECK_HR(hrTemp, ("Failed to set WPD_PROPERTY_COMMON_HRESULT"));

    // Set to a success code, to indicate that the message was received.
    // the return code for the actual command's results is stored in the
    // WPD_PROPERTY_COMMON_HRESULT property.
    hr = S_OK;

    return hr;
}