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Serves as the main interface on an undo unit. An undo unit encapsulates the information necessary to undo or redo a single action.
When an object's state changes and it needs to create an undo unit, it first needs to know what parent units are open. It calls the IOleUndoManager::GetOpenParentState method to determine this. If the call returns S_FALSE, then there is no enabling parent. If the call returns S_OK but the UAS_NOPARENTENABLE flag is set, then the open parent is a disabling parent. In either of these cases, the object calls IOleUndoManager::DiscardFrom(NULL) on the undo manager and skips creating the undo unit.
If the method returns S_OK, but the UAS_BLOCKED flag is set, then the open parent is a blocking parent. The object does not need to create an undo unit, since it would be immediately discarded. If the return value is S_OK and neither of the bit flags are set, then the object creates the undo unit and calls IOleUndoManager::Add on the undo manager.
The object should retain a pointer to the undo manager.
Inheritance
The IOleUndoUnit interface inherits from the IUnknown interface. IOleUndoUnit also has these types of members:
Methods
The IOleUndoUnit interface has these methods.
| IOleUndoUnit::Do Instructs the undo unit to carry out its action. Note that if it contains child undo units, it must call their Do methods as well. |
| IOleUndoUnit::GetDescription Retrieves a description of the undo unit that can be used in the undo or redo user interface. |
| IOleUndoUnit::GetUnitType Retrieves the CLSID and a type identifier for the undo unit. |
| IOleUndoUnit::OnNextAdd Notifies the last undo unit in the collection that a new unit has been added. |
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Windows 2000 Professional [desktop apps only] |
| Minimum supported server | Windows 2000 Server [desktop apps only] |
| Target Platform | Windows |
| Header | ocidl.h |