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Introduction
Microsoft's Active Template Library is a collection of template-based C++ classes designed to make writing Component Object Model(COM) objects easier. Microsoft Visual C++'s COM support enables developers to construct a wide range of COM objects, OLE Automation servers, and ActiveX controls. In this blog, we will be discussing service provider support classes.
Let's get started with service provider support classes.
IServiceProviderImpl Class
IServiceProviderImpl searches for a service by its GUID (Globally Unique Identifier) and returns the interface pointer for the desired interface on the service. This class executes IServiceProvider interface. IServiceProvider defines a return method for a service object, which is an object that offers specialized support to other objects.
IServiceProviderImpl provides service to other objects. Hence, the IServiceProvider interface is used here. This is implemented using the syntax given below.
template <class T>
class ATL_NO_VTABLE IServiceProviderImpl : public IServiceProvider
In the code above, the parameter ‘T’ is derived from IServiceProviderImpl.
Service Map of IServiceProviderImpl
A service map is a visual representation of a service that highlights the many elements necessary for the service's successful delivery. IServiceProviderImpl employs a service map that goes from BEGIN SERVICE MAP to END SERVICE MAP. There are two entries in the service map: SERVICE ENTRY and SERVICE ENTRY CHAIN. SERVICE ENTRY identifies a specific service id (SID) supported by the object. In contrast, SERVICE ENTRY CHAIN utilizes QueryService to chain to another object.
The following table shows the Service Map of IServiceProviderImpl of service provider support classes.
Name
Description
Syntax
Parameters
BEGIN_SERVICE_MAP
Beginning of ATL service map
BEGIN_SERVICE_MAP (theClass)
theClass [in] Defines the class that contains the service map.
END_SERVICE_MAP
End of ATL service map
END_SERVICE_MAP ()
N/A
SERVICE_ENTRY
shows that an item supports a particular service ID.
SERVICE_ENTRY ( SID )
SID The service id
SERVICE_ENTRY_CHAIN
IServiceProviderImpl ::QueryService is instructed to chain to the supplied object.
SERVICE_ENTRY_CHAIN ( punk )
punk a reference to IUnknown interface that you want to change
IServiceProviderImpl QueryService Method
IServiceProviderImpl only lists the QueryService method. It establishes or accesses the provided service. Then it returns an interface reference to the service's specified interface.
You supply a service identification (guidService) and an interface identifier when you use QueryService (riid). The guidService provides the service to which you wish to get access, and the riid identifies a service interface. You will be given an indirect reference to the interface in exchange. An indirect reference to the required interface inside the given service is returned by QueryService (HRESULT). When it is no longer needed, the caller is in charge of releasing this pointer.
The syntax of IServiceProviderImpl::QueryService is shown below.
guidService (SID) is the pointer to a service identifier.
riid is the caller's access interface's identification number.
ppvObj is the pointer to the requested interface in an indirect manner.
Return Value
In service provider support classes, one of the following HRESULT values is returned:
Return Value
Meaning
S_OK
Successful creation or retrieval of the service.
E_INVALIDARG
At least one of the arguments is untrue.
E_OUTOFMEMORY
The service cannot be created with the available memory.
E_UNEXPECTED
An unknown error occurred.
E_NOINTERFACE
The required interface is either not offered by this service or the service is unidentified.
Frequently Asked Questions
What is ATL (Active Template Library)?
Microsoft created the Active Template Library (ATL), a collection of template-based C++ classes, with the goal of making it easier to design Component Object Model (COM) objects.
What are the applications of ATL?
ActiveX controls are frequently created using the Active Template Library (ATL), a wrapper library that makes COM development easier. MFC or ATL applications may be produced with Visual Studio Community Edition or higher.
What are classes in ATL?
contains data necessary to display to a variety of destinations, like a printer, metafile, or ActiveX control. class instance data in the ATL windowing code.
What is an MFC application?
Based on the Microsoft Foundation Class (MFC) Library, an MFC application is a Windows executable programme.
What is COM object in Windows?
A distributed, object-oriented approach for developing binary software components that may communicate is known as the Microsoft Component Object Model (COM).
Conclusion
In this article, we discussed the service provider support classes (IServiceProviderImpl). We also discussed the service map and the query service functionality of IServiceProviderImpl.
After learning about service provider support classes, recommended readings are:
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