IDataObject::EnumFormatEtc

A version of this page is also available for

Windows Embedded CE 6.0 R3

4/8/2010

This method creates an object for enumerating the FORMATETC structures for a data object. These structures are used in calls to the IDataObject::GetData or IDataObject::SetData method.

Syntax

HRESULT EnumFormatEtc(
  DWORD dwDirection, 
  IEnumFORMATETC** ppenumFormatetc
);

Parameters

• dwDirection
  [in] Direction of the data through a value from the enumeration DATADIR.

  typedef enum tagDATADIR 
  { 
      DATADIR_GET = 1, 
      DATADIR_SET = 2, 
  } DATADIR; 
  

  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.

• ppenumFormatetc
  [out] Address of the IEnumFORMATETC* pointer variable that receives the interface pointer to the new enumerator object.

Return Value

This method supports the standard return values E_INVALIDARG and E_OUTOFMEMORY. The following table shows the additional return values for this method.

Remarks

IDataObject::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 supplies 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. Accordingly, applications should treat the enumeration as a hint of the format types that can be passed.

The caller is responsible for calling IEnumFormatEtc::Release when it is finished with the enumeration.

IDataObject::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.

To determine whether the platform supports this interface, see Determining Supported COM APIs.

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 OleRegEnumFormatEtc must be called 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 IDataObject::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

See Also

Reference

IEnumFORMATETC
IDataObject::GetData
IDataObject::SetData
DATADIR
FORMATETC