介绍一个UndoFramework

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; }
}


 

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

 

欢迎转载,转载请注明:转载自周金根 [ http://zhoujg.cnblogs.com/ ]

posted @ 2011-12-20 20:01  楚广明  阅读(231)  评论(0编辑  收藏  举报