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

IUnknown Methods
Returns pointers to supported interfaces.
Increments reference count.
Decrements reference count.

IPersistStorage Methods
Indicates whether the object has changed since it was last saved to its current storage.
Initializes a new storage object.
Initializes an object from its existing storage.
Saves an object, and any nested objects that it contains, into the specified storage object. The object enters NoScribble mode.
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.
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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