android（singletouch）绘图应用程序撤消方法无法正常工作

我正在开发一个绘图应用程序，但面临一些撤消问题。编码如下：

public class DoodleView extends View 
{
    Context context_new;

    private static final float TOUCH_TOLERANCE = 5;
    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 Path mPath; 
    private ArrayList<Path> paths = new ArrayList<Path>();
    private ArrayList<Path> undonePaths = new ArrayList<Path>();
    private float mX, mY;

   // DoodleView constructor initializes the DoodleView
   public DoodleView(Context context, AttributeSet attrs) 
   {
       super(context, attrs); // pass context to View's constructor
       this.context_new=context;

       paintScreen = new Paint(); // used to display bitmap onto screen

       // set the initial display settings for the painted line
       paintLine = new Paint();
       paintLine.setAntiAlias(true); // smooth edges of drawn line
       paintLine.setColor(Color.BLACK); // default color is black
       paintLine.setStyle(Paint.Style.STROKE); // solid line

       mPath = new Path();
       paths.add(mPath);

   } // end DoodleView constructor

onDraw:

   @Override
   protected void onDraw(Canvas canvas)  
   {
       canvas.drawBitmap(bitmap, 0, 0, paintScreen); 
       // for each path currently being drawn
       for (Path p : paths){canvas.drawPath(p, paintLine);}                
   } 

onTouchEvent:

   @Override
   public void onSizeChanged(int w, int h, int oldW, int oldH)
   {
      super.onSizeChanged(w, h, oldW, oldH);
      DoodlzViewWidth = w;     
      DoodlzViewHeight = h;

      bitmap = Bitmap.createBitmap(getWidth(), DoodlzViewHeight, Bitmap.Config.ARGB_8888);

      bitmapCanvas = new Canvas(bitmap);
      bitmap.eraseColor(Color.WHITE); // erase the BitMap with white 
   } 

   @Override
   public boolean onTouchEvent(MotionEvent event) 
   {          
          float x = event.getX();
          float y = event.getY();

          switch (event.getAction())
          {
              case MotionEvent.ACTION_DOWN:
                  touchStarted(x, y);
                  invalidate();
                  break;
              case MotionEvent.ACTION_MOVE:
                  touchMoved(x, y);
                  invalidate();
                  break;
              case MotionEvent.ACTION_UP:
                  touchEnded();
                  invalidate();
                  break;
          }
          return true;
    }

   private void touchStarted(float x, float y) 
   {
       mPath.reset();
       mPath.moveTo(x, y);
       mX = x;
       mY = y;
   }

   private void touchMoved(float x, float y) 
   {
       float dx = Math.abs(x - mX);
       float dy = Math.abs(y - mY);
       if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) 
       {
           mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
           mX = x;
           mY = y;               
       }
   }

   private void touchEnded() 
   {
      mPath.lineTo(mX, mY);      
      bitmapCanvas.drawPath(mPath, paintLine);
      mPath = new Path();
      paths.add(mPath);
      Toast.makeText(getContext(), "touchEnded" + paths.size(), Toast.LENGTH_SHORT).show();
   }

public void onClickUndo() 
{ 
   Toast.makeText(getContext(), "before undo button pressed " + paths.size(), Toast.LENGTH_SHORT).show();  
   if (paths.size()>0) 
    { 
       undonePaths.add(paths.remove(paths.size()-1));
       Toast.makeText(getContext(), "after undo button pressed " + paths.size(), Toast.LENGTH_SHORT).show();
       Log.i("UNDOING", "PREPARE INVALIDATE");
       invalidate();
       Log.i("UNDOING", "FINISH INVALIDATE");
    }      
   else Toast.makeText(getContext(), "nothing to undo" + paths.size(), Toast.LENGTH_SHORT).show();  
}

TouchStart:

   @Override
   public void onSizeChanged(int w, int h, int oldW, int oldH)
   {
      super.onSizeChanged(w, h, oldW, oldH);
      DoodlzViewWidth = w;     
      DoodlzViewHeight = h;

      bitmap = Bitmap.createBitmap(getWidth(), DoodlzViewHeight, Bitmap.Config.ARGB_8888);

      bitmapCanvas = new Canvas(bitmap);
      bitmap.eraseColor(Color.WHITE); // erase the BitMap with white 
   } 

   @Override
   public boolean onTouchEvent(MotionEvent event) 
   {          
          float x = event.getX();
          float y = event.getY();

          switch (event.getAction())
          {
              case MotionEvent.ACTION_DOWN:
                  touchStarted(x, y);
                  invalidate();
                  break;
              case MotionEvent.ACTION_MOVE:
                  touchMoved(x, y);
                  invalidate();
                  break;
              case MotionEvent.ACTION_UP:
                  touchEnded();
                  invalidate();
                  break;
          }
          return true;
    }

   private void touchStarted(float x, float y) 
   {
       mPath.reset();
       mPath.moveTo(x, y);
       mX = x;
       mY = y;
   }

   private void touchMoved(float x, float y) 
   {
       float dx = Math.abs(x - mX);
       float dy = Math.abs(y - mY);
       if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) 
       {
           mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
           mX = x;
           mY = y;               
       }
   }

   private void touchEnded() 
   {
      mPath.lineTo(mX, mY);      
      bitmapCanvas.drawPath(mPath, paintLine);
      mPath = new Path();
      paths.add(mPath);
      Toast.makeText(getContext(), "touchEnded" + paths.size(), Toast.LENGTH_SHORT).show();
   }

public void onClickUndo() 
{ 
   Toast.makeText(getContext(), "before undo button pressed " + paths.size(), Toast.LENGTH_SHORT).show();  
   if (paths.size()>0) 
    { 
       undonePaths.add(paths.remove(paths.size()-1));
       Toast.makeText(getContext(), "after undo button pressed " + paths.size(), Toast.LENGTH_SHORT).show();
       Log.i("UNDOING", "PREPARE INVALIDATE");
       invalidate();
       Log.i("UNDOING", "FINISH INVALIDATE");
    }      
   else Toast.makeText(getContext(), "nothing to undo" + paths.size(), Toast.LENGTH_SHORT).show();  
}

触摸移动：

   @Override
   public void onSizeChanged(int w, int h, int oldW, int oldH)
   {
      super.onSizeChanged(w, h, oldW, oldH);
      DoodlzViewWidth = w;     
      DoodlzViewHeight = h;

      bitmap = Bitmap.createBitmap(getWidth(), DoodlzViewHeight, Bitmap.Config.ARGB_8888);

      bitmapCanvas = new Canvas(bitmap);
      bitmap.eraseColor(Color.WHITE); // erase the BitMap with white 
   } 

   @Override
   public boolean onTouchEvent(MotionEvent event) 
   {          
          float x = event.getX();
          float y = event.getY();

          switch (event.getAction())
          {
              case MotionEvent.ACTION_DOWN:
                  touchStarted(x, y);
                  invalidate();
                  break;
              case MotionEvent.ACTION_MOVE:
                  touchMoved(x, y);
                  invalidate();
                  break;
              case MotionEvent.ACTION_UP:
                  touchEnded();
                  invalidate();
                  break;
          }
          return true;
    }

   private void touchStarted(float x, float y) 
   {
       mPath.reset();
       mPath.moveTo(x, y);
       mX = x;
       mY = y;
   }

   private void touchMoved(float x, float y) 
   {
       float dx = Math.abs(x - mX);
       float dy = Math.abs(y - mY);
       if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) 
       {
           mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
           mX = x;
           mY = y;               
       }
   }

   private void touchEnded() 
   {
      mPath.lineTo(mX, mY);      
      bitmapCanvas.drawPath(mPath, paintLine);
      mPath = new Path();
      paths.add(mPath);
      Toast.makeText(getContext(), "touchEnded" + paths.size(), Toast.LENGTH_SHORT).show();
   }

public void onClickUndo() 
{ 
   Toast.makeText(getContext(), "before undo button pressed " + paths.size(), Toast.LENGTH_SHORT).show();  
   if (paths.size()>0) 
    { 
       undonePaths.add(paths.remove(paths.size()-1));
       Toast.makeText(getContext(), "after undo button pressed " + paths.size(), Toast.LENGTH_SHORT).show();
       Log.i("UNDOING", "PREPARE INVALIDATE");
       invalidate();
       Log.i("UNDOING", "FINISH INVALIDATE");
    }      
   else Toast.makeText(getContext(), "nothing to undo" + paths.size(), Toast.LENGTH_SHORT).show();  
}

touchEnded:

   @Override
   public void onSizeChanged(int w, int h, int oldW, int oldH)
   {
      super.onSizeChanged(w, h, oldW, oldH);
      DoodlzViewWidth = w;     
      DoodlzViewHeight = h;

      bitmap = Bitmap.createBitmap(getWidth(), DoodlzViewHeight, Bitmap.Config.ARGB_8888);

      bitmapCanvas = new Canvas(bitmap);
      bitmap.eraseColor(Color.WHITE); // erase the BitMap with white 
   } 

   @Override
   public boolean onTouchEvent(MotionEvent event) 
   {          
          float x = event.getX();
          float y = event.getY();

          switch (event.getAction())
          {
              case MotionEvent.ACTION_DOWN:
                  touchStarted(x, y);
                  invalidate();
                  break;
              case MotionEvent.ACTION_MOVE:
                  touchMoved(x, y);
                  invalidate();
                  break;
              case MotionEvent.ACTION_UP:
                  touchEnded();
                  invalidate();
                  break;
          }
          return true;
    }

   private void touchStarted(float x, float y) 
   {
       mPath.reset();
       mPath.moveTo(x, y);
       mX = x;
       mY = y;
   }

   private void touchMoved(float x, float y) 
   {
       float dx = Math.abs(x - mX);
       float dy = Math.abs(y - mY);
       if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) 
       {
           mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
           mX = x;
           mY = y;               
       }
   }

   private void touchEnded() 
   {
      mPath.lineTo(mX, mY);      
      bitmapCanvas.drawPath(mPath, paintLine);
      mPath = new Path();
      paths.add(mPath);
      Toast.makeText(getContext(), "touchEnded" + paths.size(), Toast.LENGTH_SHORT).show();
   }

public void onClickUndo() 
{ 
   Toast.makeText(getContext(), "before undo button pressed " + paths.size(), Toast.LENGTH_SHORT).show();  
   if (paths.size()>0) 
    { 
       undonePaths.add(paths.remove(paths.size()-1));
       Toast.makeText(getContext(), "after undo button pressed " + paths.size(), Toast.LENGTH_SHORT).show();
       Log.i("UNDOING", "PREPARE INVALIDATE");
       invalidate();
       Log.i("UNDOING", "FINISH INVALIDATE");
    }      
   else Toast.makeText(getContext(), "nothing to undo" + paths.size(), Toast.LENGTH_SHORT).show();  
}

撤消：

   @Override
   public void onSizeChanged(int w, int h, int oldW, int oldH)
   {
      super.onSizeChanged(w, h, oldW, oldH);
      DoodlzViewWidth = w;     
      DoodlzViewHeight = h;

      bitmap = Bitmap.createBitmap(getWidth(), DoodlzViewHeight, Bitmap.Config.ARGB_8888);

      bitmapCanvas = new Canvas(bitmap);
      bitmap.eraseColor(Color.WHITE); // erase the BitMap with white 
   } 

   @Override
   public boolean onTouchEvent(MotionEvent event) 
   {          
          float x = event.getX();
          float y = event.getY();

          switch (event.getAction())
          {
              case MotionEvent.ACTION_DOWN:
                  touchStarted(x, y);
                  invalidate();
                  break;
              case MotionEvent.ACTION_MOVE:
                  touchMoved(x, y);
                  invalidate();
                  break;
              case MotionEvent.ACTION_UP:
                  touchEnded();
                  invalidate();
                  break;
          }
          return true;
    }

   private void touchStarted(float x, float y) 
   {
       mPath.reset();
       mPath.moveTo(x, y);
       mX = x;
       mY = y;
   }

   private void touchMoved(float x, float y) 
   {
       float dx = Math.abs(x - mX);
       float dy = Math.abs(y - mY);
       if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) 
       {
           mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
           mX = x;
           mY = y;               
       }
   }

   private void touchEnded() 
   {
      mPath.lineTo(mX, mY);      
      bitmapCanvas.drawPath(mPath, paintLine);
      mPath = new Path();
      paths.add(mPath);
      Toast.makeText(getContext(), "touchEnded" + paths.size(), Toast.LENGTH_SHORT).show();
   }

public void onClickUndo() 
{ 
   Toast.makeText(getContext(), "before undo button pressed " + paths.size(), Toast.LENGTH_SHORT).show();  
   if (paths.size()>0) 
    { 
       undonePaths.add(paths.remove(paths.size()-1));
       Toast.makeText(getContext(), "after undo button pressed " + paths.size(), Toast.LENGTH_SHORT).show();
       Log.i("UNDOING", "PREPARE INVALIDATE");
       invalidate();
       Log.i("UNDOING", "FINISH INVALIDATE");
    }      
   else Toast.makeText(getContext(), "nothing to undo" + paths.size(), Toast.LENGTH_SHORT).show();  
}

问题： 以上内容来源于在线搜索的其他示例。不知道在实现

touchStarted

时为什么需要设置path.reset（）

问题1。当我按下undo the按钮时，它将正确显示按下的

toast

undo按钮，并报告

path.size（）

为0，因此前面绘制的直线未被删除。我真的不知道为什么是0？？它不是已经添加到路径数组中了吗？如何修改代码

**在采纳android开发者的建议后修改了代码！谢谢它现在可以正确显示path.size（）。很抱歉我错过了！*但上一条绘制的线仍然无法删除=（

Q2.当手指在屏幕上移动并立即显示线条时，应用程序运行正常，但当我按下“撤消”按钮时，除了上面提到的前一行没有被删除之外，按下按钮后，线条进一步拉到屏幕上，直到手指抬起，才会显示出来

第二季度的答案： 将以下两行从

touchEnded（）

移动到

touchStart（）

谢谢！！！

更新并生效：

去除油漆网

在onDraw中，不要放置

canvas.drawBitmap（位图，0，0，paintScreen）；

或

canvas.drawBitmap（位图，0，0，paintLine）；

---

我看不到

路径。在
mPath.reset（）；
之后添加（mPath）；

。将当前路径添加到arraylist的位置？感谢您的建议！！我已修改了愚蠢的遗漏错误！路径。大小（）现在可以正确显示，即，当再画一条线时，大小将增加1。但是之前的路径仍然无法删除（尽管toast undo显示），并且按下按钮时会产生奇怪的绘图效果：直到手指被删除，绘制时才会显示线。您是说即使是路径。size（）大于0时，按下的

undo按钮将显示toast？undo part Codeing已更新..如果绘制了4行，它将显示“undo button pressed4”。感谢您的及时回复~您能帮我检查一下吗？按下undo按钮后，它是否真的从arraylist中删除了最后一条路径，并且正在调用
onDraw（）
无效（）后的方法
？