# IConnectionPoint

The IConnectionPoint interface supports connection points for connectable objects.

Connectable objects support the following features:

- Outgoing interfaces, such as event sets

- The ability to enumerate the IIDs of the outgoing interfaces

- The ability to connect and disconnect sinks to the object for those outgoing IIDs

- The ability to enumerate the connections that exist to a particular outgoing interface

##### When to Implement

Implement this interface as part of support for connectable objects. To create a connectable object, you need to implement objects that provide four related interfaces:

- IConnectionPointContainer

- IEnumConnectionPoints

- IConnectionPoint

- IEnumConnections

The IConnectionPointContainer interface is implemented on the connectable object to indicate the existence of the outgoing interfaces. It provides access to an enumerator sub-object with the IEnumConnectionPoints interface. It also provides access to all the connection point sub-objects, each of which implements the IConnectionPoint interface. The IConnectionPoint interface provides access to an enumerator sub-object with the IEnumConnections interface.

Each connection point is a separate sub-object to avoid circular reference counting problems.

A connection point controls how many connections (one or more) it will allow in its implementation of IConnectionPoint::Advise. A connection point that allows only one interface can return E_NOTIMPL from the IConnectionPoint::EnumConnections method.

##### When to Use

A client can use the IConnectionPointContainer interface:

- To obtain access to an enumerator sub-object with the IEnumConnectionPoints interface. The IEnumConnectionPoints interface can then be used to enumerate connection points for each outgoing IID.

- To obtain access to connection point sub-objects with the IConnectionPoint interface for each outgoing IID. Through the IConnectionPoint interface, a client starts or terminates an advisory loop with the connectable object and the client’s own sink. The client can also use the IConnectionPoint interface to obtain an enumerator object with the IEnumConnections interface to enumerate the connections that it knows about.

Methods in Vtable Order

IUnknown Methods | Description
QueryInterface | Returns pointers to supported interfaces.
AddRef | Increments reference count.
Release | Decrements reference count.

IConnectionPoint Methods | Description
GetConnectionInterface | Returns the IID of the outgoing interface managed by this connection point.
GetConnectionPointContainer | Returns the parent (connectable) object’s IConnectionPointContainer interface pointer.
Advise | Creates a connection between a connection point and a client’s sink, where the sink implements the outgoing interface supported by this connection point.
Unadvise | Terminates a notification previously set up with Advise.
EnumConnections | Returns an object to enumerate the current advisory connections for this connection point.

See Also

IConnectionPoint, IConnectionPointContainer, IEnumConnectionPoints, IEnumConnections