Supply undo support to designers
Designers, like editors, typically need to support undo operations so that users can reverse their recent changes when modifying a code element.
Most designers implemented in Visual Studio have "undo" support automatically provided by the environment.
Designer implementations that need to provide support for the undo feature:
Provide undo management by implementing the abstract base class UndoEngine
Supply persistence and CodeDOM support by implementing the IDesignerSerializationService and IComponentChangeService classes.
For more information on writing designers using .NET Framework, see Extend Design-Time Support.
The Visual Studio SDK provides a default undo infrastructure by:
Providing undo management implementations through the OleUndoEngine and OleUndoEngine.UndoUnit classes.
Supplying persistence and CodeDOM support through the default CodeDomComponentSerializationService and IComponentChangeService implementations.
Obtain Undo Support Automatically
Any designer created in Visual Studio has automatic and full undo support if, the designer:
Makes use of a Control based class for its user interface.
Employs standard CodeDOM-based code generation and parsing system for code generation and persistence.
For more information about working with Visual Studio CodeDOM support, see Dynamic Source Code Generation and Compilation.
When to Use Explicit Designer Undo Support
Designers must supply their own undo management if they use a graphical user interface, referred to as a view adapter, other than the one supplied by Control.
An example of this might be creating a product with a web-based graphical design interface rather than a .NET Framework-based graphical interface.
In such cases, one would need to register this view adapter with Visual Studio using ProvideViewAdapterAttribute, and provide explicit undo management.
Designers need to provide CodeDOM and persistence support if they do not use the Visual Studio code generation model provided in the System.CodeDom name space.
Undo Support Features of the Designer
The Environment SDK provides default implementations of interfaces needed to provide undo support that can be used by designers not using Control based classes for their user interfaces or the standard CodeDOM and persistence model.
The OleUndoEngine class derives from the .NET Framework UndoEngine class using an implementation of the IOleUndoManager class to manage undo operations.
Visual Studio provides the following feature to designer undo:
Linked undo functionality across multiple designers.
Child units within a designer can interact with their parents by implementing IOleUndoUnit and IOleParentUndoUnit on OleUndoEngine.UndoUnit.
The Environment SDK provides CodeDOM and persistence support by supplying:
CodeDomComponentSerializationService as an implementation of the IDesignerSerializationService
A IComponentChangeService provided by the Visual Studio design host.
Use the Environment SDK Features to Supply Undo Support
To obtain undo support, an object implementing a designer must instantiate and initialize an instance of the OleUndoEngine class with a valid IServiceProvider implementation. This IServiceProvider class must provide the following services:
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Designers using Visual Studio CodeDOM serialization may choose to use CodeDomComponentSerializationService provided with the Visual Studio SDK as its implementation of the IDesignerSerializationService.
In this case, the IServiceProvider class provided to the OleUndoEngine constructor should return this object as an implementation of the IDesignerSerializationService class.
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Designers using the default DesignSurface provided by the Visual Studio design host are guaranteed to have a default implementation of the IComponentChangeService class.
Designers implementing a OleUndoEngine based undo mechanism automatically tracks changes if:
Property changes are made through the TypeDescriptor object.
IComponentChangeService events are manually generated when an undoable change is committed.
Modification on the designer was created within the context of a DesignerTransaction.
The designer chooses to explicitly create undo units using either the standard undo unit provided by an implementation of UndoEngine.UndoUnit or the Visual Studio-specific implementation OleUndoEngine.UndoUnit, which derives from UndoEngine.UndoUnit and also provides an implementation of both IOleUndoUnit and IOleParentUndoUnit.