Android：用橡皮擦画应用不起作用

Question

我正在一个绘画应用程序，与撤消/重做功能，并希望添加橡皮擦功能。

case R.id.undoBtn:          
     doodleView.onClickUndo();          
     break;

case R.id.redoBtn:          
     doodleView.onClickRedo();          
     break;

case R.id.eraserBtn:            
     Constants.mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT)); break; 

// Drawing Part    
    private Bitmap mBitmap;   
    private Paint  mBitmapPaint;
    private Canvas mCanvas; 
    private Path   mPath; 
    private int selectedColor = Color.BLACK;
    private int selectedWidth = 5;

    private ArrayList<Path> paths = new ArrayList<Path>();
    private ArrayList<Path> undonePaths = new ArrayList<Path>();
    private Map<Path, Integer> colorsMap = new HashMap<Path, Integer>();
    private Map<Path, Integer> widthMap = new HashMap<Path, Integer>();

    private float mX, mY;
    private static final float TOUCH_TOLERANCE = 4; 
    Context context_new;

   public DoodleView(Context c, AttributeSet attrs) 
   {
       super(c, attrs);
       context_new = c;    
       setFocusable(true);
       setFocusableInTouchMode(true);
       setLayerType(View.LAYER_TYPE_SOFTWARE, null); // for solely removing the black eraser

       mPath = new Path(); 
       mCanvas = new Canvas();  
       mBitmapPaint = new Paint(Paint.DITHER_FLAG);   

       Constants.mPaint = new Paint();
       Constants.mPaint.setAntiAlias(true); // smooth edges of drawn line
       Constants.mPaint.setDither(true);
       Constants.mPaint.setColor(Color.BLACK); // default color is black
       Constants.mPaint.setStyle(Paint.Style.STROKE); // solid line
       Constants.mPaint.setStrokeJoin(Paint.Join.ROUND);
       Constants.mPaint.setStrokeWidth(20); // set the default line width
       Constants.mPaint.setStrokeCap(Paint.Cap.ROUND); // rounded line ends 
       Constants.mPaint.setXfermode(null);
       Constants.mPaint.setAlpha(0xFF);
   } 

   @Override
   public void onSizeChanged(int w, int h, int oldW, int oldH)
   {
       super.onSizeChanged(w, h, oldW, oldH);
       mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);

      Constants.DRAW_W = w;
      Constants.DRAW_H = h;
      Log.d("TAG", "onSizeChanged!!!" + Constants.DRAW_W + Constants.DRAW_H + Constants.SCREEN_W + Constants.SCREEN_H);   
      // bitmap.eraseColor(Color.WHITE); // erase the BitMap with white    
   }   

   @Override
   protected void onDraw(Canvas canvas) 
   {
       canvas.drawBitmap(mBitmap, 0, 0, null); // draw the background screen

       for (Path p : paths)
       {
           Constants.mPaint.setColor(colorsMap.get(p));
           Constants.mPaint.setStrokeWidth(widthMap.get(p));
           canvas.drawPath(p, Constants.mPaint);           
       }       
       Constants.mPaint.setColor(selectedColor);
       Constants.mPaint.setStrokeWidth(selectedWidth);
       canvas.drawPath(mPath, Constants.mPaint);                   
   } 

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

          switch (event.getAction())
          {
              case MotionEvent.ACTION_DOWN:
                   touch_start(x, y);
                   invalidate();
                   break;
              case MotionEvent.ACTION_MOVE:
                   touch_move(x, y);
                   invalidate();
                   break;
              case MotionEvent.ACTION_UP:
                   touch_up();
                   invalidate();
                   break;
          }
          return true;
    }

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

   private void touch_move(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;

           startdrawing = true;
       }
   }

   private void touch_up() 
   {
       mPath.lineTo(mX, mY);      
       mCanvas.drawPath(mPath, Constants.mPaint); 
       paths.add(mPath);
       colorsMap.put(mPath,selectedColor);
       widthMap.put(mPath,selectedWidth);
       mPath = new Path(); 
   }

   public void onClickUndo() 
   { 
       if (paths.size()>0) 
        { 
           undonePaths.add(paths.remove(paths.size()-1));
           invalidate();
        }      
       else Toast.makeText(getContext(), R.string.toast_nothing_to_undo, Toast.LENGTH_SHORT).show();  
    }

   public void onClickRedo()
   {
       if (undonePaths.size()>0) 
       { 
           paths.add(undonePaths.remove(undonePaths.size()-1)); 
           invalidate();
       } 
       else 
           Toast.makeText(getContext(), R.string.toast_nothing_to_redo, Toast.LENGTH_SHORT).show(); 
    }  

   public void setDrawingColor(int color)
   {       
       selectedColor = color;
       Constants.mPaint.setColor(color);
   } 

   public int getDrawingColor()
   {
      return Constants.mPaint.getColor();
   } 

橡皮擦上的代码怎么写得合适？（保留撤消/重做）

提前多谢！

Answer 1

很难回答你的问题，但是。我将按以下方式实现擦除功能：

擦除功能将由简单的白色路径。因此，擦除模式意味着您正在绘制比绘制路径更宽的白色路径。这样，您就可以选择橡皮擦的宽度，并且撤消/重做功能将保持不变。