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Using IConnectionPoint

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When the client has a pointer to a connection point, it can perform the following operations as expressed through IConnectionPoint:

  • First, IConnectionPoint::GetConnectionInterface retrieves the outgoing interface IID supported by the connection point. When used in conjunction with IEnumConnectionPoints, this method allows the client to examine the IIDs of all outgoing interfaces supported on the connectable object.
  • Second, a client can navigate from the connection point back to the connectable object's IConnectionPointContainer interface through the IConnectionPoint::GetConnectionPointContainer method.
  • Third, the most interesting methods for the client are IConnectionPoint::Advise and IConnectionPoint::Unadvise. When a client wishes to connect its own sink object to the connectable object, the client passes the sink's IUnknown pointer (or any other interface pointer on the same object) to Advise. The connection point queries the sink for the specific outgoing interface that is expected. If that interface is available on the sink, the connection point then stores the interface pointer. From this point until Unadvise is called, the connectable object will make calls to the sink through this interface when events occur. To disconnect the sink from the connection point, the client passes a key returned from Advise to the Unadvise method. Unadvise must call Release on the sink interface.
  • Finally, a client can ask a connection point to enumerate all the connections to it that exist through IConnectionPoint::EnumConnections. This method creates an enumerator object (with a separate reference count) returning an IEnumConnections pointer to it. The client must call Release when the enumerator is no longer needed. Additionally, the enumerator returns a series of CONNECTDATA structures, one for each connection. Each structure describes one connection using the IUnknown pointer of the sink as well as the connection key originally returned from Advise. When done with these sink interface pointers, the client must call Release on each pointer returned in a CONNECTDATA structure.

Connectable Object Interfaces