Windows 8：如何使用内置的墨迹功能撤消和重做墨迹？

Question

我已经根据 microsoft 的简化墨迹示例在我的应用中实现墨迹书写代码：http://code.msdn.microsoft.com/windowsapps/Input-simplified-ink-sample-11614bbf/view/SourceCode

首先我创建了一个类来保存操作（绘制/删除/清除）的数据，如下所示：

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;
    }
}

然后我做了一个堆栈用于撤消墨迹操作和一个用于重做操作

//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>();

当用户撤消笔画时，我将其推送到重做堆栈并使用以下方法从 inkmanager 中删除：

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时，笔画从重做堆栈中弹出并使用此方法绘制：

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());
}

这一切都奏效了，笔画又显示在网格上。 但是，当我尝试擦除新重绘的笔画时，我得到了这个异常：

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));

我认为问题在于向墨迹管理器添加笔画的过程。我尝试制作一个新的笔画，甚至从 InkStroke 继承以使其可定制，但 InkStroke 类是密封的并且它没有构造函数。我发现复制它的唯一方法是执行 inkStroke.Clone()。但即便如此，在尝试重绘已删除的墨迹（撤消已删除的笔划）时也会出现问题。

我试图用最少的代码尽可能清楚地说明这个问题以避免混淆，所以如果不够，请告诉我。

此外，在这个问题中，我将重点放在撤消平局操作上。撤消擦除操作（甚至“清除所有”操作）有其自身的一系列问题，因为我无法复制 InkStroke 对象。

提前感谢您的时间和考虑。

Answer 1

请参阅来自 MSDN 的 this 线程，这可能会有所帮助。