The IPersistFile interface provides methods for an object to load and save itself in a disk file, instead of saving itself to a storage object. Because the information needed to open a file varies greatly from one application to another, the object must be responsible for opening its disk file.

When to Implement

The IPersistFile interface is implemented by any object or container application that can be linked through a file moniker, including the following:

  • Any object that supports links to its files or to pseudo-objects within its files

  • A container application that supports links to component objects within its compound file

Typically, you implement the IPersistFile interface as part of an aggregate object that includes other interfaces that are appropriate for the type of moniker binding that is supported.

For example, in either of the cases mentioned above, the moniker for the linked object can be a composite moniker. In the first case, a composite moniker identifies the pseudo-object contained within the file. In the second case, a composite moniker identifies the embedded object contained within the compound file. In either case of composite monikers, you must implement the IPersistFile interface as part of same object that also implements the IOleItemContainer interface. Then, when the application for the linked object is run, OLE queries for the IOleItemContainer interface to locate the embedded object or the pseudo-object contained in the file.

As another example, if the moniker is a simple file moniker (i.e., the link is to the entire file), OLE queries for the interface that the initiator of the bind operation requested. Typically, this is one of the compound document interfaces, such as IOleObject, IDataObject, or IPersistStorage.

When to Use

You call methods in the IPersistFile interface to load or save a linked component object in a specified file.

When the application for the linked object is run, OLE calls the IPersistFile::Load method. Once the file is loaded, OLE calls IPersistFile::QueryInterface to get another interface pointer to the loaded object. The IPersistFile interface is typically part of an aggregate object that offers other interfaces.

Note that OLE calls only the IPersistFile::Load method. It does not call any of the other IPersistFile methods. Typically, applications do not call these methods either. The IPersistFile::Load method enables OLE to load a file on behalf of a container application when the container needs to run the application for the linked object. The other IPersistFile methods support saving a component to a file, but container applications do not tell a linked object to save itself. It is entirely up to the end user and the application for the linked object to decide when the component should be saved. This differs from the situation for an embedded component, in which the container application uses the IPersistStorage interface to provide the storage and to tell the component when to save itself.

Methods in Vtable Order

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

IPersistFile Methods
Checks an object for changes since it was last saved to its current file.
Opens the specified file and initializes an object from the file contents.
Saves the object into the specified file.
Notifies the object that it can revert from NoScribble mode to Normal mode.
Gets the current name of the file associated with the component.

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