android(singletouch)绘图应用程序撤消方法无法正常工作

Question

我正在开发一个绘图应用程序，但遇到一些撤消问题。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

OnSizeChanged:

   @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 
   } 

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 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;
    }

touchStarted:

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

触摸移动:

   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;               
       }
   }

触摸结束:

   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();
   }

撤消:

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:

以上内容来源于网上搜索到的其他例子。不知道为什么在实现touchStarted时需要设置path.reset()？

Q1。当我按下撤消按钮时，它会正确显示 toast 撤消按钮已按下，并报告 path.size() 为 0，因此之前立即绘制的线未删除。我真的不知道为什么它是0？它不是已经添加到路径数组了吗？如何修改代码？

** 在听取了 android 开发者的建议后修改了代码!谢谢!!它现在正确显示 path.size()。抱歉，愚蠢的错过了!* 但是之前画的线仍然无法删除？ =(

Q2。当手指在屏幕上移动并立即显示线条时应用程序正常运行时，当我按下撤消按钮时，除了上面没有删除上一行之外，按下后线条进一步绘制到屏幕上在手指抬起之前，按钮不会显示出来。

Q2 的答案:将以下两行从 touchEnded() 移动到 touchStarted()

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

.

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

   private void touchEnded() 
   {
       mPath.lineTo(mX, mY);      
       bitmapCanvas.drawPath(mPath, paintLine);// commit the path to our offscreen                   
       Toast.makeText(getContext(), "touchEnded" + paths.size(), Toast.LENGTH_SHORT).show();
   }

谢谢!!!

Answer 1

更新和工作:

1. 移除了 Paint paintScreen；

2. 在 onDraw 中不要放置 canvas.drawBitmap(bitmap, 0, 0, paintScreen); 或 canvas.drawBitmap(bitmap, 0, 0, paintLine);

   private Bitmap bitmap; // drawing area for display or saving
   private Canvas bitmapCanvas; // used to draw on bitmap
   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;
   private static final float TOUCH_TOLERANCE = 4;    
   
   // DoodleView constructor initializes the DoodleView
   
   public DoodleView(Context context, AttributeSet attrs) 
   {
      super(context, attrs); // pass context to View's constructor
      this.context_new=context;
      setFocusable(true);
      setFocusableInTouchMode(true);      
   
      // set the initial display settings for the painted line
      paintLine = new Paint();
      paintLine.setAntiAlias(true); // smooth edges of drawn line
      paintLine.setDither(true);
      paintLine.setColor(Color.BLACK); // default color is black
      paintLine.setStyle(Paint.Style.STROKE); // solid line
      paintLine.setStrokeJoin(Paint.Join.ROUND);
      paintLine.setStrokeWidth(5); // set the default line width
      paintLine.setStrokeCap(Paint.Cap.ROUND); // rounded line ends
   
      bitmapCanvas = new Canvas();
      mPath = new Path();            
    } // end DoodleView constructor
   
    // Method onSizeChanged creates BitMap and Canvas after app displays
   
    @Override
    public void onSizeChanged(int w, int h, int oldW, int oldH)
    {
       super.onSizeChanged(w, h, oldW, oldH);
       DoodlzViewWidth = w;       
       DoodlzViewHeight = h;           
    } 
   
    @Override
   
    protected void onDraw(Canvas canvas) 
    {         
      for (Path p : paths){canvas.drawPath(p, paintLine);}  
      canvas.drawPath(mPath, paintLine);
      Log.i("OnDRAWING", "REACH ON DRAW");        
   } 
   

   //START TOUCH:处理触摸事件 @覆盖

    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;
       }
   }  
   
   private void touch_up() 
   {
       mPath.lineTo(mX, mY);      
       bitmapCanvas.drawPath(mPath, paintLine);// commit the path to our offscreen  
       paths.add(mPath);
       mPath = new Path(); 
   }
   
   public void onClickUndo() 
   { 
      if (paths.size()>0) 
       { 
          undonePaths.add(paths.remove(paths.size()-1));
          invalidate();
       }      
      else Toast.makeText(getContext(), "nothing more to undo", Toast.LENGTH_SHORT).show();  
   }