IDataObject::EnumFormatEtc method (objidl.h)

Artykuł
10/13/2021

Creates an object to enumerate the formats supported by a data object.

Syntax

HRESULT EnumFormatEtc(
  [in]  DWORD          dwDirection,
  [out] IEnumFORMATETC **ppenumFormatEtc
);

Parameters

[in] dwDirection

The direction of the data. Possible values come from the DATADIR enumeration.

The value DATADIR_GET enumerates the formats that can be passed in to a call to IDataObject::GetData. The value DATADIR_SET enumerates those formats that can be passed in to a call to IDataObject::SetData.

[out] ppenumFormatEtc

A pointer to an IEnumFORMATETC pointer variable that receives the interface pointer to the new enumerator object.

Return value

This method returns S_OK on success. Other possible values include the following.

Return code	Description
E_INVALIDARG	The supplied dwDirection is invalid.
E_OUTOFMEMORY	Insufficient memory available for this operation.
E_NOTIMPL	The direction specified by dwDirection is not supported.
OLE_S_USEREG	Requests that OLE enumerate the formats from the registry.

Remarks

EnumFormatEtc creates an enumerator object that can be used to determine all of the ways the data object can describe data in a FORMATETC structure, and provides a pointer to its IEnumFORMATETC interface. This is one of the standard enumerator interfaces.

Notes to Callers

Having obtained the pointer, the caller can enumerate the FORMATETC structures by calling the enumeration methods of IEnumFORMATETC. Because the formats can change over time, there is no guarantee that an enumerated format is currently supported because the formats can change over time. Accordingly, applications should treat the enumeration as a hint of the format types that can be passed. The caller is responsible for calling Release when it is finished with the enumerator.

EnumFormatEtc is called when one of the following actions occurs:

An application calls OleSetClipboard. OLE must determine what data to place on the clipboard and whether it is necessary to put OLE 1 compatibility formats on the clipboard.
Data is being pasted from the clipboard or dropped. An application uses the first acceptable format.
The Paste Special dialog box is displayed. The target application builds the list of formats from the FORMATETC entries.

Notes to Implementers

Formats can be registered statically in the registry or dynamically during object initialization. If an object has an unchanging list of formats and these formats are registered in the registry, OLE provides an implementation of a FORMATETC enumeration object that can enumerate formats registered under a specific CLSID in the registry. A pointer to its IEnumFORMATETC interface is available through a call to the helper function OleRegEnumFormatEtc. In this situation, therefore, you can implement the EnumFormatEtc method simply with a call to this function.

EXE applications can effectively do the same thing by implementing the method to return the value OLE_S_USEREG. This return value instructs the default object handler to call OleRegEnumFormatEtc. Object applications that are implemented as DLL object applications cannot return OLE_S_USEREG, so must call OleRegEnumFormatEtc directly.

Private formats can be enumerated for OLE 1 objects, if they are registered with the RequestDataFormats or SetDataFormats keys in the registry. Also, private formats can be enumerated for OLE objects (all versions after OLE 1), if they are registered with the GetDataFormats or SetDataFormats keys.

For OLE 1 objects whose servers do not have RequestDataFormats or SetDataFormats information registered in the registry, a call to EnumFormatEtc passing DATADIR_GET only enumerates the native and metafile formats, regardless of whether they support these formats or others. Calling EnumFormatEtc passing DATADIR_SET on such objects only enumerates native, regardless of whether the object supports being set with other formats.

The FORMATETC structure returned by the enumeration usually indicates a NULL target device (ptd). This is appropriate because, unlike the other members of FORMATETC, the target device does not participate in the object's decision as to whether it can accept or provide the data in either a SetData or GetData call.

The tymed member of FORMATETC often indicates that more than one kind of storage medium is acceptable. You should always mask and test for this by using a Boolean OR operator.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	objidl.h

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