android(多点触控)绘图app撤消功能

声明：

int tHelastLinEID=0;
private Bitmap bitmap; // drawing area for display or saving
private Canvas bitmapCanvas; // used to draw on bitmap
private Paint paintScreen; // use to draw bitmap onto screen
private Paint paintLine; // used to draw lines onto bitmap
private HashMap<Integer,Path> pathMap; // current Paths being drawn
private HashMap<Integer,Path> reservedpathMap; // for saving the paths being undone
private HashMap<Integer,Point> prevIoUsPointMap; // current Points

构造函数：

pathMap = new HashMap<Integer,Path>();
reservedpathMap = new HashMap <Integer,Path>(); // for storing path being undone
prevIoUsPointMap = new HashMap<Integer,Point>();

onDraw有：

@Override
   protected void onDraw(Canvas canvas) 
   {
       canvas.drawBitmap(bitmap,paintScreen);
       // for each path currently being drawn
       for (Integer key : pathMap.keySet()) 
            canvas.drawPath(pathMap.get(key),paintLinE); // draw line     
   }

的onTouchEvent：

@Override
   public Boolean onTouchEvent(MotionEvent event) 
   {                  
      int action = event.getActionMasked(); // event type 
      int actionIndex = event.getActionIndex(); // pointer (i.e.,finger)

      if (action == MotionEvent.ACTION_DOWN) 
      {       
          touchStarted(event.getX(actionIndeX),event.getY(actionIndeX),event.getPointerId(actionIndeX));
      } 
      else if (action == MotionEvent.ACTION_Up) 
      {
          touchEnded(event.getPointerId(actionIndeX));
      } 
      else 
      {
         touchMoved(event); 
      } 

      invalidate();
      return true; 
   }

touchStarted：

private void touchStarted(float x,float y,int linEID) // linEID represents how many fingers,1 finger 1 line
   {      
      Path path; // used to store the path for the given touch id
      Point point; // used to store the last point in path

      // if there is already a path for linEID
      if (pathMap.containsKey(linEID)) 
      {
         path = pathMap.get(linEID); // get the Path
         path.reset(); // reset the Path because a new touch has started
         point = prevIoUsPointMap.get(linEID); // get Path's last point
      } 
      else 
      {
         path = new Path(); // create a new Path
         pathMap.put(linEID,path); // add the Path to Map
         point = new Point(); // create a new Point
         prevIoUsPointMap.put(linEID,point); // add the Point to the Map
      } 

      path.moveTo(x,y);
      point.x = (int) x;  
      point.y = (int) y;  
   }

touchMoved：

private void touchMoved(MotionEvent event) 
   {
      // for each of the pointers in the given MotionEvent
      for (int i = 0; i < event.getPointerCount(); i++) 
      {
         // get the pointer ID and pointer index
         int pointerID = event.getPointerId(i);
         int pointerIndex = event.findPointerIndex(pointerID);

         // if there is a path associated with the pointer
         if (pathMap.containsKey(pointerID)) 
         {
            float newX = event.getX(pointerIndeX);
            float newY = event.getY(pointerIndeX);

            // get the Path and prevIoUs Point associated with this pointer
            Path path = pathMap.get(pointerID);
            Point point = prevIoUsPointMap.get(pointerID);

            float deltaX = Math.abs(newX - point.X);
            float deltaY = Math.abs(newY - point.y);
            if (deltaX >= TOUCH_TOLERANCE || deltaY >= TOUCH_TOLERANCE) 
            {
               path.quadTo(point.x,point.y,((newX + point.X)/2),((newY + point.y)/2));

               point.x = (int) newX ; 
               point.y = (int) newY ; 
         } 
      }      
   }

touchEnded：

private void touchEnded(int linEID)
   {
      Path path = pathMap.get(linEID); // get the corresponding Path
      bitmapCanvas.drawPath(path,paintLinE); 
      path.reset();           
   }

撤消：

public void undo()
   {
       Toast.makeText(getContext(),"undo button pressed" + tHelastLinEID,Toast.LENGTH_SHORT).show();

       Path path = pathMap.get(tHelastLinEID); 
       reservedpathMap.put(tHelastLinEID,path); // add the Path to reservedpathMap for later redo
       pathMap.remove(tHelastLinEID);   

       invalidate();          
   }

题：

我正在尝试使用如上所示的代码实现UNDO方法：尝试从HashMap路径图中删除tHelastLindId键(并将其放到HashMap后面的稍后重做的路径映射),这样当invalidate()时它将调用OnDraw()并且重绘

for (Integer key : pathMap.keySet()) 
                canvas.drawPath(pathMap.get(key),paintLinE);

但是,按下撤消按钮可以启动“撤消被点击”的祝酒,但最后绘制的行无法消失.

有人可以给我一个Undo()和Redo()的线索吗？提前谢谢了！！