IPersistStorage
The
IPersistStorage interface enables a container application to pass a storage object to one of
its contained objects and to load and save the storage object. This interface
supports the structured storage scheme in which each component object has its
own storage that is nested within the container's storage.
When to Implement
Any object that can be embedded in a container object must implement the
IPersistStorage interface. This interface is one of the primary interfaces for a compound
document object. It is part of the aggregate object that includes the
IOleObject and
IDataObject interfaces.
The OLE default handler for embedded objects provides an implementation of the
IPersistStorage interface that is used when the object is in the loaded state. Similarly, the
OLE default link handler provides an
IPersistStorage implementation that manages storage for a linked object. These default
handlers both interact with the OLE default cache implementation, which has its own
IPersistStorage implementation.
If you are providing a custom embedding or link handler for your objects, the
handler must include an implementation of
IPersistStorage. You can delegate calls to the default handler so you can take advantage of
the default cache implementation.
When to Use
When an OLE container creates a new object, loads an existing object from
storage, or inserts a new object in a clipboard or a drag-and-drop operation, the
container uses the
IPersistStorage interface to initialize the object and put it in the loaded or running state.
When a component is loaded or running, an OLE container uses the other
IPersistStorage methods to instruct the component to perform various save operations or to
instruct the component to release its storage.
Typically, applications use helper functions such as
OleLoad or
OleCreate, rather than calling the
IPersistStorage::Load or
IPersistStorage::InitNew methods directly. Similarly, applications typically call the
OleSave helper function rather than calling
IPersistStorage::Save directly.
Methods in Vtable Order
IPersistStorage Methods
| Description
|
IsDirty
| Indicates whether the object has changed since it was last saved to its
current storage.
|
InitNew
| Initializes a new storage object.
|
Load
| Initializes an object from its existing storage.
|
Save
| Saves an object, and any nested objects that it contains, into the specified
storage object. The object enters NoScribble mode.
|
SaveCompleted
| Notifies the object that it can revert from NoScribble or HandsOff mode, in
which in must not write to its storage object, to Normal mode in which it can.
|
HandsOffStorage
| Instructs the object to release all storage objects that have been passed to
it by its container and to enter HandsOffAfterSave or HandsOffFromNormal mode.
|
See Also
IDataObject,
IOleObject,
OleCreate,
OleLoad,
OleSave
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