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connection-maps.md

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Learn more about: Connection Maps
Connection Maps
8/1/2023
connection maps

Connection maps

OLE controls are able to expose interfaces to other applications. These interfaces only allow access from a container into that control. If an OLE control wants to access external interfaces of other OLE objects, a connection point must be established. This connection point allows a control outgoing access to external dispatch maps, such as event maps or notification functions.

The Microsoft Foundation Class Library offers a programming model that supports connection points. In this model, "connection maps" are used to designate interfaces or connection points for the OLE control. Connection maps contain one macro for each connection point. For more information on connection maps, see the CConnectionPoint class.

Typically, a control supports just two connection points: one for events and one for property notifications. These are implemented by the COleControl base class and require no extra work by the control writer. Any other connection points you want to implement in your class must be added manually. To support connection maps and points, MFC provides the following macros:

Connection Map declaration and demarcation

Name Description
BEGIN_CONNECTION_PART Declares an embedded class that implements an additional connection point (must be used in the class declaration).
END_CONNECTION_PART Ends the declaration of a connection point (must be used in the class declaration).
CONNECTION_IID Specifies the interface ID of the control's connection point.
DECLARE_CONNECTION_MAP Declares that a connection map will be used in a class (must be used in the class declaration).
BEGIN_CONNECTION_MAP Begins the definition of a connection map (must be used in the class implementation).
END_CONNECTION_MAP Ends the definition of a connection map (must be used in the class implementation).
CONNECTION_PART Specifies a connection point in the control's connection map.

The following functions assist a sink in establishing and disconnecting a connection using connection points:

Initialization/termination of connection points

Name Description
AfxConnectionAdvise Establishes a connection between a source and a sink.
AfxConnectionUnadvise Breaks a connection between a source and a sink.

BEGIN_CONNECTION_PART

Use the BEGIN_CONNECTION_PART macro to begin the definition of additional connection points beyond the event and property notification connection points.

BEGIN_CONNECTION_PART(theClass, localClass)

Parameters

theClass Specifies the name of the control class whose connection point this is.

localClass Specifies the name of the local class that implements the connection point.

Remarks

In the declaration (.h) file that defines the member functions for your class, start the connection point with the BEGIN_CONNECTION_PART macro. Then add the CONNECTION_IID macro and any other member functions you wish to implement. Finally, complete the connection point map with the END_CONNECTION_PART macro.

Requirements

Header afxdisp.h

END_CONNECTION_PART

Ends the declaration of your connection point.

END_CONNECTION_PART(localClass)

Parameters

localClass
Specifies the name of the local class that implements the connection point.

Requirements

Header afxdisp.h

CONNECTION_IID

Use between the BEGIN_CONNECTION_PART and END_CONNECTION_PART macros to define an interface ID for a connection point supported by your OLE control.

CONNECTION_IID(iid)

Parameters

iid
The interface ID of the interface called by the connection point.

Remarks

The iid argument is an interface ID used to identify the interface that the connection point calls on its connected sinks. For example:

[!code-cppNVC_MFCConnectionPoints#10]

Specifies a connection point that calls the ISinkInterface interface.

Requirements

Header afxdisp.h

DECLARE_CONNECTION_MAP

Each COleControl-derived class in your program can provide a connection map to specify additional connection points that your control supports.

DECLARE_CONNECTION_MAP()

Remarks

If your control supports additional points, use the DECLARE_CONNECTION_MAP macro at the end of your class declaration. Then, in the .cpp file that defines the member functions for the class, use the BEGIN_CONNECTION_MAP macro, CONNECTION_PART macros for each of the control's connection points, and the END_CONNECTION_MAP macro to declare the end of the connection map.

Requirements

Header afxdisp.h

BEGIN_CONNECTION_MAP

Each COleControl-derived class in your program can provide a connection map to specify connection points that your control will support.

BEGIN_CONNECTION_MAP(theClass, theBase)

Parameters

theClass
Specifies the name of the control class whose connection map this is.

theBase
Specifies the name of the base class of theClass.

Remarks

In the implementation (.CPP) file that defines the member functions for your class, start the connection map with the BEGIN_CONNECTION_MAP macro, then add macro entries for each of your connection points using the CONNECTION_PART macro. Finally, complete the connection map with the END_CONNECTION_MAP macro.

Requirements

Header afxdisp.h

END_CONNECTION_MAP

Ends the definition of your connection map.

END_CONNECTION_MAP()

Requirements

Header afxdisp.h

CONNECTION_PART

Maps a connection point for your OLE control to a specific interface ID.

CONNECTION_PART(theClass, iid, localClass)

Parameters

theClass
Specifies the name of the control class whose connection point this is.

iid
The interface ID of the interface called by the connection point.

localClass
Specifies the name of the local class that implements the connection point.

Remarks

For example:

[!code-cppNVC_MFCConnectionPoints#2]

implements a connection map, with a connection point, that calls the IID_ISinkInterface interface.

Requirements

Header afxdisp.h

AfxConnectionAdvise

Call this function to establish a connection between a source, specified by pUnkSrc, and a sink, specified by pUnkSink.

BOOL AFXAPI AfxConnectionAdvise(
    LPUNKNOWN pUnkSrc,
    REFIID iid,
    LPUNKNOWN pUnkSink,
    BOOL bRefCount,
    DWORD FAR* pdwCookie);

Parameters

pUnkSrc
A pointer to the object that calls the interface.

pUnkSink
A pointer to the object that implements the interface.

iid
The interface ID of the connection.

bRefCount
For out-of-process connections, this parameter must be TRUE, and indicates that creating the connection should cause the reference count of pUnkSink to be incremented.

For in-process connections, TRUE indicates that creating the connection should cause the reference count of pUnkSink to be incremented. FALSE indicates that the reference count shouldn't be incremented.

Warning: In general, it can't be predicted which connections are in-process and which connections are out-of-process, so it is recommended to always set this parameter to TRUE.

pdwCookie
A pointer to a DWORD where a connection identifier is returned. This value should be passed as the dwCookie parameter to AfxConnectionUnadvise when disconnecting the connection.

Return Value

Nonzero if a connection was established; otherwise 0.

Example

[!code-cppNVC_MFCConnectionPoints#8]

Requirements

Header: afxctl.h

AfxConnectionUnadvise

Call this function to disconnect a connection between a source, specified by pUnkSrc, and a sink, specified by pUnkSink.

BOOL AFXAPI AfxConnectionUnadvise(
    LPUNKNOWN pUnkSrc,
    REFIID iid,
    LPUNKNOWN pUnkSink,
    BOOL bRefCount,
    DWORD dwCookie);

Parameters

pUnkSrc
A pointer to the object that calls the interface.

pUnkSink
A pointer to the object that implements the interface.

iid
The interface ID of the connection point interface.

bRefCount
For out-of-process connections, this parameter must be TRUE, and indicates that creating the connection should cause the reference count of pUnkSink to be decremented.

For in-process connections, TRUE indicates that creating the connection should cause the reference count of pUnkSink to be decremented. FALSE indicates that the reference count shouldn't be decremented.

Warning: In general, it can't be predicted which connections are in-process and which connections are out-of-process, so it is recommended to always set this parameter to TRUE.

dwCookie
The connection identifier returned by AfxConnectionAdvise.

Return value

Nonzero if a connection was disconnected; otherwise 0.

Example

[!code-cppNVC_MFCConnectionPoints#9]

Requirements

Header: afxctl.h

See also

Macros and Globals