由于其他工作，好多天又没有对MetaModelEngine进行思考了，这两天又腾出时间可以思考一下了，本篇介绍一下在图形编辑器中对操作如何实现Undo操作。
在图形设计器操作中，每个操作按钮都对应到一个命令，很多情况下我们都应该允许用户执行操作后回滚这些操作，或者回滚后又再次执行。在我做的报表引擎中，我是在每次操作后把设计文件都保留下来，这个在报表设计中是没有问题，但是在毕竟不是很好的设计。接下来要考虑对OpenExpressApp提供建模支持了，所以也需要考虑一下如何让图形设计器更好的支持这种Undo操作。
在公司的一个项目组中内部是使用命令模式，只是在传统命令模式中增加了一个UnExecute方法，这个方法就是用来做Undo操作的。在codeplex上我找到了一类似的轻量级UndoFramework，后期准备就用它了，在这里我就给大家介绍一下。
UndoFramework项目
Codeplex网站地址：http://undo.codeplex.com/
下载地址：http://undo.codeplex.com/releases/view/29440
项目描述：
It's a simple framework to add Undo/Redo functionality to your applications, based on the classical Command design pattern. It supports merging actions, nested transactions, delayed execution (execution on top-level transaction commit) and possible non-linear undo history (where you can have a choice of multiple actions to redo).
The status of the project is Stable (released). I might add more stuff to it later, but right now it fully satisfies my needs. It's implemented in C# 3.0 (Visual Studio 2008) and I can build it for both desktop and Silverlight. The release has both binaries.
现有应用
A good example of where this framework is used is the Live Geometry project (http://livegeometry.codeplex.com). It defines several actions such as AddFigureAction, RemoveFigureAction, MoveAction and SetPropertyAction.
如何使用
我学习这些东西一般都喜欢先看如何使用，因为从使用方式就能看出封装得是否简单易用。
以下是一个控制台的演示程序，代码如下：
运行后界面如下：
下载代码你会看到，它还自带一个Form的例子，感兴趣可以自己去看看
Actions
所有操作都从 IAction继承下来，必须实现两个操作：一个是执行操作，一个是反执行操作
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/// <summary>
/// Encapsulates a user action (actually two actions: Do and Undo)
/// Can be anything.
/// You can give your implementation any information it needs to be able to
/// execute and rollback what it needs.
/// </summary>
public
interface
IAction
{
/// <summary>
/// Apply changes encapsulated by this object.
/// </summary>
void
Execute();
/// <summary>
/// Undo changes made by a previous Execute call.
/// </summary>
void
UnExecute();
/// <summary>
/// For most Actions, CanExecute is true when ExecuteCount = 0 (not yet executed)
/// and false when ExecuteCount = 1 (already executed once)
/// </summary>
/// <returns>true if an encapsulated action can be applied</returns>
bool
CanExecute();
/// <returns>true if an action was already executed and can be undone</returns>
bool
CanUnExecute();
/// <summary>
/// Attempts to take a new incoming action and instead of recording that one
/// as a new action, just modify the current one so that it's summary effect is
/// a combination of both.
/// </summary>
/// <param name="followingAction"></param>
/// <returns>true if the action agreed to merge, false if we want the followingAction
/// to be tracked separately</returns>
bool
TryToMerge(IAction followingAction);
/// <summary>
/// Defines if the action can be merged with the previous one in the Undo buffer
/// This is useful for long chains of consecutive operations of the same type,
/// e.g. dragging something or typing some text
/// </summary>
bool
AllowToMergeWithPrevious {
get
;
set
; }
}
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ActionManager
ActionManager负责跟踪undo/redo记录，提供RecordAction(IAction)来记录操作步骤，提供ActionManager.Undo(), ActionManager.Redo(), CanUndo(), CanRedo()等其他方法。
其完整代码如下：
参考
http://blogs.msdn.com/kirillosenkov/archive/2009/06/29/new-codeplex-project-a-simple-undo-redo-framework.aspx
http://blogs.msdn.com/kirillosenkov/archive/2009/07/02/samples-for-the-undo-framework.aspx
其他Undo框架
- http://dejavu.codeplex.com/ by Sergei Arhipenko
- http://www.codeproject.com/KB/cs/undoredobuffer.aspx by Marc Clifton
- http://msmvps.com/blogs/matthieu/archive/2009/06/08/ef-undo-redo.aspx - Undo/Redo for Entity Framework by Matthieu MEZIL
欢迎转载，转载请注明：转载自周金根 [ http://zhoujg.cnblogs.com/ ]
