IAdviseSink::OnDataChange

Notifies a data object's currently registered advise sinks that data in the object has changed.

oid OnDataChange(

FORMATETC * pFormatetc,	//Pointer to format information
STGMEDIUM * pStgmed	//Pointer to storage medium
);

Parameters
pFormatetc

[in] Points to the FORMATETC structure, which describes the format, target device, rendering, and storage information of the calling data object.
pStgmed

[in] Points to the STGMEDIUM structure, which defines the storage medium (global memory, disk file, storage object, stream object, GDI object, or undefined) and ownership of that medium for the calling data object.

Comments
Object handlers and link objects implement IAdviseSink::OnDataChange to receive data-change notifications. They also must call IDataObject::DAdvise to set up an advisory connection with the data objects in which they are interested. (See IDataObject::DAdvise for more information on how to specify an advisory connection for data objects.)

Containers that take advantage of OLE's caching support do not need to register for data-change notifications, because the information necessary to update the container's presentation of the object, including any changes in its data, are maintained in the object's cache.

Notes to Implementors
If you implement IAdviseSink::OnDataChange for a container, remember that this method is asynchronous and that making synchronous calls within asynchronous methods is not valid. Therefore, you cannot call IDataObject::GetData to obtain the data you need to update your object. Instead, you either post an internal message or invalidate the rectangle for the changed data by calling InvalidateRect and then wait for a WM_PAINT message, at which point you are free to get the data and update the object.

The data itself, which is valid only for the duration of the call, is passed using the storage medium pointed to by pmedium. Since the medium is owned by the caller, the advise sink should not free it. Also, if pmedium points to an IStorage or IStream, the sink must not increment the reference count.