Paint.Net笔记(X3) Action 与 HistoryFunction

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上一篇介绍了ToolForm的操作机制, 这一篇看一下菜单项的操作.

看ImageMenus.cs会发现如下代码

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private void MenuImageCrop_Click(object sender, System.EventArgs e)
{
	if (AppWorkspace.ActiveDocumentWorkspace != null)
	{
		if (!AppWorkspace.ActiveDocumentWorkspace.Selection.IsEmpty)
		{
			AppWorkspace.ActiveDocumentWorkspace.ExecuteFunction(new CropToSelectionFunction());
		}
	}
}

private void MenuImageResize_Click(object sender, System.EventArgs e)
{
	if (AppWorkspace.ActiveDocumentWorkspace != null)
	{
		AppWorkspace.ActiveDocumentWorkspace.PerformAction(new ResizeAction());
	}
}

有些菜单项是ExecuteFunction, 有些菜单项是PerformAction. 各种Action和Function如下图所示
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)
ResizeAction继承DocumentWorkspaceAction, CropToSelectionFunction继承HistoryFunctiont

另外AppWorkspace也能执行Action

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private void MenuFileOpen_Click(object sender, System.EventArgs e)
{
	AppWorkspace.PerformAction(new OpenFileAction());
}

OpenFileAction继承AppWorkspaceAction, 另外有些Action不继承其他类.

它们之间的区别是什么?

DocumentWorkspaceAction与AppWorkspaceAction的区别, 一个是作用的对象不同, 另一个是DocumentWorkspaceAction还能够撤销(命令模式+备忘录模式). 如下所示

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   internal abstract class AppWorkspaceAction
   {
       public abstract void PerformAction(AppWorkspace appWorkspace);

       public AppWorkspaceAction()
       {
           SystemLayer.Tracing.LogFeature("AWAction(" + GetType().Name + ")");
       }
   }


/// <summary>
   /// Provides a way to do a tool-less action that operates on the DocumentWorkspace.
   /// DocumentActions must NOT touch directly the History -- they should return history 
   /// actions that can undo what they have already done. These history actions will
   /// then be placed in to the history by whomever invoked the DocumentAction.
   /// If the action does not affect the Document, it should return null from its
   /// PerformAction method.
   /// DocumentActions should ONLY mutate the DocumentWorkspace and any contained
   /// objects.
   /// </summary>
   internal abstract class DocumentWorkspaceAction
   {
       private ActionFlags actionFlags;
       public ActionFlags ActionFlags
       {
           get
           {
               return this.actionFlags;
           }
       }

       /// <summary>
       /// Implement this to provide an action. You must return a HistoryMemento so that you
       /// can be undone. However, you should return null if you didn't do anything that
       /// affected the document.
       /// </summary>
       /// <returns>A HistoryMemento object that will be placed onto the HistoryStack.</returns>
       public abstract HistoryMemento PerformAction(DocumentWorkspace documentWorkspace);

       /// <summary>
       /// Initializes an instance of a class dervied from DocumentAction.
       /// </summary>
       /// <param name="documentWorkspace">The DocumentWorkspace to interact with.</param>
       /// <param name="actionFlags">Flags that describe action behavior or requirements.</param>
       public DocumentWorkspaceAction(ActionFlags actionFlags)
       {
           this.actionFlags = actionFlags;
           SystemLayer.Tracing.LogFeature("DWAction(" + GetType().Name + ")");
       }
   }

那HistoryFunction呢? HistoryFunction与DocumentWorkspaceAction有什么不同

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public HistoryMemento Execute(IHistoryWorkspace historyWorkspace);
public abstract HistoryMemento OnExecute(IHistoryWorkspace historyWorkspace);

从前面2张图片对比, 从名称上看, HistoryFunction貌似更多在和layer和selection打交道.