IServiceProvider locates a service specified by its GUID and returns the interface pointer for the requested interface on the service.

When to Implement

An object that provides services should implement the IServiceProvider interface as a general way to supply its clients with interface pointers to the interfaces on the service.

A service is often provided through a separate object from the client site. For example, the service can be provided through a separate control or some other object that the client can communicate with.

Usually, the client communicates through its client site object in the container. The container calls IOleObject::SetClientSite to provide a pointer to the IOleClientSite interface for the embedded objectÆs client site. Then, the client must call methods in the IOleClientSite interface to find out about services that its container supports. Thus, the client site must provide a way for the client to access the service when necessary, even if the service is provided through a separate object.

For example, an in-place object calls IOleInPlaceSite::GetWindowContext to obtain interface pointers for the document object that contains the site and for the frame object that contains the document. Both of these interface pointers are on objects separate from the site object, so the client cannot call IOleInPlaceSite::QueryInterface to obtain these interface pointers.

The IServiceProvider interface is a general way to provide interface pointers for services, so that the site object need not implement ad hoc solutions as the need arises.

When to Use

This interface itself has only one method, IServiceProvider::QueryService. The caller specifies a GUID for the service and the IID of the requested interface. The interface pointer is returned in a caller-supplied variable.

Methods in Vtable Order

IUnknown Methods                          Description                                  
                                                                                       

QueryInterface                            

Returns pointers to supported interfaces.    
                                                                                       

AddRef                                    Increments the reference count.              
                                                                                       

Release                                   Decrements the reference count.              
                                                                                       

IServiceProvider Methods                  Description                                  
                                                                                       

QueryService                              

Returns an interface pointer to the requested 
                                          interface on a service.                       
                                                                                       

See Also