Windows 8：如何使用内置的墨迹功能撤消和重做墨迹？

Question

我已经通过微软实现着墨代码的基础上简化墨样品我的应用程序：http://code.msdn.microsoft.com/windowsapps/Input-simplified-ink-sample-11614bbf/view/SourceCode

首先我做了一个类，节省了操作的数据（平局/删除/清除）是这样的：

public enum eInkOperation 
{ 
    Draw, 
    Delete, 
    None 
} 

public class InkOperation 
{ 
    public InkStroke Stroke { get; set; } //requred for drawing from undo 
    public eInkOperation Operation { get; set; } 

    public InkOperation(InkStroke stroke, eInkOperation inkOperation) 
    { 
     Stroke = stroke.Clone(); //needs to be cloned for AddStroke to work 
     Operation = inkOperation; 
    } 
} 

然后我为撤消墨操作中的一个堆，一个用于重做操作

//stack of normal operations 
Stack<InkOperation> _undoStack = new Stack<InkOperation>(); 
//Undo action will pop them off of the undo stack and push them onto the redo stack 
Stack<InkOperation> _redoStack = new Stack<InkOperation>(); 

当用户撤消行程我推重做堆栈上和从这些方法的inkmanager删除：

private void RedoStackPush(InkOperation inkOperation) 
{ 
    inkOperation.Stroke = inkOperation.Stroke.Clone(); 
    _redoStack.Push(inkOperation); 
} 

    private void DeleteStroke(InkStroke stroke) 
    {        
     stroke = inkManager.GetStrokes().Last(); 
     stroke.Selected = true; 
     inkManager.DeleteSelected(); 
    } 

然后，当用户点击重做，笔划被弹出重做堆栈和使用该方法绘制：

private void DrawStroke(InkStroke stroke) 
{ 
     if (stroke!=null) 
     { 
      inkManager.Mode = InkManipulationMode.Inking; 
      inkManager.AddStroke(stroke); 
     } 
     renderer.Clear(); //this renderer object smooths the strokes 
     //and adds them as Path objects to the desired control (Grid, etc) 
     renderer.AddInk(inkManager.GetStrokes()); 
} 

这一切工作，并且显示回行程上的网格。 然而，当我试图抹掉新重绘行程我得到这个异常：

AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt. 

这发生在：

public void PointerMoved(PointerRoutedEventArgs e) 
{ 
    try 
    { 
     var pointerPoint = e.GetCurrentPoint(_inkingArea); 
     var pointerEventType = InkHelpers.GetPointerEventType(e); 
     if (pointerId == (int)pointerPoint.PointerId) 
     { 
      switch (inkManager.Mode) 
      { 
       case InkManipulationMode.Inking: 
       case InkManipulationMode.Selecting: 
        //process intermediate points 
        var intermediatePoints = e.GetIntermediatePoints(_inkingArea); 
        for (int i = intermediatePoints.Count - 1; i >= 0; i--) 
        { 
         inkManager.ProcessPointerUpdate(intermediatePoints[i]); 
        } 
        //live rendering 
        renderer.UpdateLiveRender(pointerPoint); 
        break; 
       case InkManipulationMode.Erasing: 
        //check if something has been erased 
        //in erase mode InkManager.ProcessPointerUpdate returns an invalidate rectangle: 
        //if it is not degenerate, something has been erased 
        //in erase mode don't bother processing intermediate points 

        //If inkManager.ProcessPointerUpdate throws an exception, it crashes the app regardless of any catches 
        Rect invalidateRect = (Rect)inkManager.ProcessPointerUpdate(e.GetCurrentPoint(_inkingArea)); 
        if (invalidateRect.Height != 0 && invalidateRect.Width != 0) 
        { 
         //we don't know what has been erased so we clear the render 
         //and add back all the ink saved in the ink manager 
         renderer.Clear(); 

         var remainingStrokes = inkManager.GetStrokes(); 
         renderer.AddInk(remainingStrokes); 
        } 
        break; 
       default: 
        break; 
      } 
     } 
    } 
    catch (Exception) { } 
} 

在这一行：

Rect invalidateRect = (Rect)inkManager.ProcessPointerUpdate(e.GetCurrentPoint(_inkingArea)); 

我觉得问题位于向笔墨管理器添加笔触的过程中。我尝试制作一个新笔画，甚至从InkStroke继承以使其可定制，但InkStroke类是密封的，并且没有构造函数。唯一的是我发现复制它是做inkStroke.Clone（）。但即使如此，在尝试重新绘制已删除的墨迹时也会遇到问题（撤消已删除的笔触）。

我试着用尽可能少的代码来尽量清楚这个问题以避免混淆，所以让我知道它是否不足。

同样在这个问题中，我专注于撤消抽签动作。撤消擦除动作（或者甚至“清除所有”动作）有它自己的一套问题，因为我无法复制InkStroke对象。

预先感谢您的时间和考虑。

Answer 1

请参阅this来自MSDN的线程，这可能会有所帮助。