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