IDataObject::DAdvise

Creates a connection between a data object and an advise sink so the advise sink can receive notifications of changes in the data object.

HRESULT DAdvise(

FORMATETC * pFormatetc,	//Description of data that is of interest to the advise sink
DWORD advf,	//Flags that specify how the notification takes place
IAdviseSink * pAdvSink,	//The advise sink that is requesting notification
DWORD * pdwConnection	//Identifies the connection for future calls to the Unadvise method
);

Parameters

pFormatetc

[in]Points to the particular format, target device, aspect, and medium that will be used for future notifications. For example, one sink may want to know only when the bitmap representation of the data in the the data object changes. Another sink may be interested in only the metafile format of the same object. Each advise sink is notified when the data of interest changes. This data is passed back to the advise sink when notification occurs.

advf

[in]Contains a group of flags for controlling the advisory connection. Valid values are from the enumeration ADVF. However, only some of the possible ADVF values are relevant for this method. The following table briefly describes the relevant values. You can find a more detailed description in ADVF.

ADVF Value	Description
ADVF_NODATA	Asks the data object to avoid sending data with the notifications. Typically data is sent. This flag is a way to override the default behavior. When ADVF_NODATA is used, the TYMED member of the STGMEDIUM structure that is passed to OnDataChange will usually contain TYMED_NULL. The caller can then retrieve the data with a subsequent IDataObject::GetData call.
ADVF_ONLYONCE	Causes the advisory connection to be destroyed after the first change notification is sent. An implicit call to IDataObject::DUnadvise is made on behalf of the caller to remove the connection.
ADVF_PRIMEFIRST	Asks for an additional initial notification. The combination of ADVF_ONLYONCE and ADVF_PRIMEFIRST provides, in effect, an asynchronous IDataObject::GetData call.
ADVF_DATAONSTOP	When specified with ADVF_NODATA, this flag causes a last notification with the data included to to be sent before the data object is destroyed. If used without ADVF_NODATA, IDataObject::DAdvise can be implemented in one of the following ways:
	the ADVF_DATAONSTOP can be ignored.
	the object can behave as if ADVF_NODATA was specified.
	a change notification is sent only in the shutdown case. Data changes prior to shutdown do not cause a notification to be sent.

pAdvSink

[in]Points to the advisory sink that will receive the change notification.

pdwConnection

[in]Points to the location of a returned token that identifies this connection. You can use this token later to delete the advisory connection (by passing it to IDataObject::DUnadvise). If this value is zero, the connection was not established.

Return Values

S_OK

The advisory connection was created.

E_INVALIDARG

One or more arguments are invalid.

E_UNEXPECTED

An unexpected error occurred.

E_OUTOFMEMORY

The connection was not created because the system ran out of memory.

E_NOTIMPL

This method is not implemented for the data object.

DV_E_LINDEX

Invalid value for lindex; currently, only -1 is supported.

DV_E_FORMATETC

Invalid value for pFormatetc.

OLE_E_ADVISENOTSUPPORTED

The data object does not support change notification.

Comments

The IDataObject::DAdvise method creates a connection between the data object and the caller. The caller provides an advisory sink through which the notifications can be sent when the object's data changes. The advise sink issues the call to IDataObject::DAdvise. Advisory connections are associated with a particular description of the data. Data clients specify the format, aspect, medium, and/or target device of interest in the FORMATETC structure passed in. If the data object does not support one or more of the requested attributes or the sending of notifications at all. It can refuse the connection by returning OLE_E_ADVISENOTSUPPORTED.

Objects used for data transfer typically do not support advisory notifications and return OLE_E_ADVISENOTSUPPORTED from IDataObject::DAdvise.

Containers of linked objects can set up advisory connections directly with the bound link source or indirectly via the standard OLE link object that manages the connection. Connections set up with the bound link source are not automatically deleted. The container must explicitly call IDataObject::DUnAdvise on the bound link source to delete it. Connections set up through the OLE link object are destroyed when the link object is deleted.

The OLE default link object creates a "wildcard advise" with the link source so OLE can maintain the time of last change. This advise is specifically used to note the time that anything changed. OLE ignores all data formats that may have changed, noting only the time of last change. To allow wildcard advises, set the FORMATETC members as follows before calling IDataObject::DAdvise:

cf == 0;

ptd == NULL;

dwAspect ==-1;

lindex == -1

tymed == -1;

The advise flags should also include ADVF_NODATA. Wildcard advises from OLE should always be accepted by applications.

For those data objects that support notifications, a data advise holder object can be used to simplify the implementation of DAdvise and the other notification methods in IDataObject (DUnadvise and EnumAdvise). The data advise holder is an object provided by OLE that manages the registration and sending of notifications. With the first invocation of DAdvise, the helper function CreateDataAdviseHolder can be called to create the data advise holder and provide the data object with a pointer to it. The data object then delegates to the IDataAdviseHolder::Advise method in the data advise holder to create the requested connection.

See also

ADVF, FORMATETC, CreateDataAdviseHolder, IAdviseSink::OnDataChange, IDataObject::DUnAdvise

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