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android canvas 删除之前绘制的路径

转载 作者：塔克拉玛干 更新时间：2023-11-02 08:02:49 29 4
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我正在制作一个绘图应用程序，并想实现一个撤消功能以删除紧邻的先前绘制的路径。

编码:

private HashMap<Integer, Path> pathMap; // current Paths being drawn
private HashMap<Integer, Point> previousPointMap; // current Points
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

public DrawView(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
      paintLine.setStrokeWidth(5); // set the default line width
      paintLine.setStrokeCap(Paint.Cap.ROUND); // rounded line ends
      pathMap = new HashMap<Integer, Path>();
      previousPointMap = new HashMap<Integer, Point>();
} // end DrawView constructor

@Override
protected void onDraw(Canvas canvas)  
{
    canvas.drawBitmap(bitmap, 0, 0, paintScreen); 
    for (Integer key : pathMap.keySet()) 
    canvas.drawPath(pathMap.get(key), paintLine);
} 

// called when the user finishes a touch    
   private void touchEnded(int lineID)   
   {
      Path path = pathMap.get(lineID); // get the corresponding Path
      bitmapCanvas.drawPath(path, paintLine); // draw to bitmapCanvas
      path.reset(); // reset the Path
      rememberLineId = lineID;
   } // end method touch_ended

//undo       
   private void undo()
   {
      Path path = pathMap.get(rememberLineId); // get the corresponding Path
      pathMap.remove(rememberLineId);
      bitmapCanvas.clearPath(path, paintLine); 
      path.reset(); // reset the Path
   }

问题:

不过，好像没有bitmapCanvas.clearPath这个方法？如果可以，怎么修改？

代码修改:

声明:

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, Point> previousPointMap; // current Points

private Bitmap bitmapBackup;

OnSizeChanged

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

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

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

FirsttoBackup 方法，将在下面的 TouchedStart 执行时调用

public void firsttobackup()
{ 
   bitmapBackup=bitmap;
       Toast message = Toast.makeText(getContext(), "backuped 123", Toast.LENGTH_SHORT);
   message.show(); //THIS TOAST CAN BE SUCESSFULLY PRESENTED when touching screen starting to draw
}

画图

@Override
protected void onDraw(Canvas canvas) 
{
canvas.drawBitmap(bitmap, 0, 0, paintScreen); 
    for (Integer key : pathMap.keySet()) 
     canvas.drawPath(pathMap.get(key), paintLine);

}

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 || action == MotionEvent.ACTION_POINTER_DOWN) 
  {
      firsttobackup(); //TOAST CAN SHOW "BACKUP 123"

      touchStarted(event.getX(actionIndex), event.getY(actionIndex), 
        event.getPointerId(actionIndex));
  }

撤消:用户按下撤消按钮将调用此操作

public void undo()
{
  bitmap = bitmapBackup.copy(Bitmap.Config.ARGB_8888, true);
  bitmapCanvas = new Canvas(bitmap);        
}

修改问题:

现在使用方法 firsttobackup()，这样 bitmapBackup 在执行 OnTouchEvent touchStarted 时会设置 = bitmap。我已经在其中 toast ，当用户按下屏幕并开始绘制时，它成功呈现“备份 123”。

当用户点击撤消按钮时，它会调用撤消方法，但是现在按下撤消按钮，看不到任何 Action ...为什么？

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