# IOleCache::Cache

Specifies the format and other data to be cached inside an embedded object.

HRESULT Cache(

FORMATETC * pFormatetc, | //Pointer to the format and data to be cached
DWORD advf, | //Flags that control the caching
DWORD * pdwConnection | //Pointer to the connection for future calls to uncache
); |

Parameters

pFormatetc
  [in] Pointer to the format and other data to be cached. View caching is specified by passing a zero clipboard format in pFormatetc.
advf
  [in] Contains a group of flags that control the caching. Valid values can be derived by using an OR operation on the values in the ADVF enumeration. When used in this context, for a cache, these values have specific meanings, which are outlined in the Remarks. Refer to the ADVF enumeration for a more detailed description.
pdwConnection
  [out] Pointer to a returned DWORD token that identifies this connection and can later be used to turn caching off (by passing it to IOleCache::Uncache). If this value is zero, the connection was not established. The OLE-provided implementation uses nonzero numbers for connection identifiers.

Return Values

This method supports the standard return values E_INVALIDARG, E_OUTOFMEMORY, and E_UNEXPECTED, as well as the following:

S_OK
  Requested data or view successfully cached.
CACHE_S_FORMATETC_NOTSUPPORTED
  The cache was created, but the object application does not support the specified format. Cache creation succeeds even if the format is not supported, allowing the caller to fill the cache. If, however, the caller does not need to keep the cache, call IOleCache::UnCache.
CACHE_S_SAMECACHE
  A cache already exists for the FORMATETC passed to IOleCache::Uncache. In this case, the new advise flags are assigned to the cache, and the previously assigned connection identifier is returned.
DV_E_LINDEX
  Invalid value for lindex; currently only -1 is supported.
DV_E_TYMED
  The value is not valid for pFormatetc->tymed.
DV_E_DVASPECT
  The value is not valid for pFormatetc->dwAspect.
DV_E_CLIPFORMAT
  The value is not valid for pFormatetc->cfFormat.
CO_E_NOTINITIALIZED
  The cache’s storage is not initialized.
DV_E_DVTARGETDEVICE
  The value is not valid for pFormatetc->ptd.
OLE_E_STATIC
  The cache is for a static object and it already has a cache node.

Remarks

IOleCache::Cache can specify either data caching or view (presentation) caching. To specify data caching, a valid data format must be passed in pFormatetc. For view caching, the cache object itself decides on the format to cache, so a caller would pass a zero data format in pFormatetc as follows:

    pFormatetc->cfFormat == 0

A custom object handler can choose not to store data in a given format. Instead, it can synthesize it on demand when requested.

The advf value specifies a member of the ADVF enumeration. When one of these values (or an OR’d combination of more than one value) is used in this context, these values mean the following:

ADVF Value | Description
ADVF_NODATA | The cache is not to be updated by changes made to the running object. Instead, the container will update the cache by explicitly calling IOleCache::SetData, IDataObject::SetData, or IOleCache2::UpdateCache. This flag is usually used when the iconic aspect of an object is being cached.
ADVF_ONLYONCE | Update the cache one time only. After the update is complete, the advisory connection between the object and the cache is disconnected. The source object for the advisory connection calls the IAdviseSink::Release method.
ADVF_PRIMEFIRST | The object is not to wait for the data or view to change before updating the cache. OR’d with ADVF_ONLYONCE, this parameter provides an asynchronous GetData call.
ADVFCACHE_NOHANDLER | Synonym for ADVFCACHE_FORCEBUILTIN.
ADVFCACHE_FORCEBUILTIN | Used by DLL object applications and object handlers that draw their objects to cache presentation data to ensure that there is a presentation in the cache. This ensures that the data can be retrieved even when the object or handler code is not available.
ADVFCACHE_ONSAVE | Updates the cached representation only when the object containing the cache is saved. The cache is also updated when the OLE object changes from the running state back to the loaded state (because a subsequent save operation would require running the object again).

See Also

ADVF, IOleCache::Uncache