Question

我正在制作一个绘图应用程序，但我不知道为什么当从图库加载图片时，当进一步绘制时，刚刚绘制的线将出现在Touch上，但当手指离开屏幕时会消失，即绘制的线不能固定在Bitmap上。

有没有人知道如何修改它？非常感谢!!!

编码：

public class DrawView extends View  // the main screen that is painted
{
   private static final float TOUCH_TOLERANCE = 10;

   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   

   public DrawView(Context context, AttributeSet attrs) 
   {
      super(context, attrs);     
      paintScreen = new Paint(); 

      // set the default settings
      paintLine = new Paint();
      paintLine.setColor(Color.BLACK); 
      paintLine.setStyle(Paint.Style.STROKE);
      paintLine.setStrokeWidth(5);
      pathMap = new HashMap<Integer, Path>();
      previousPointMap = new HashMap<Integer, Point>();
   }

   // Method onSizeChanged creates BitMap and Canvas after app displays
   @Override
   public void onSizeChanged(int w, int h, int oldW, int oldH)
   {
      bitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
      bitmapCanvas = new Canvas(bitmap);
      bitmap.eraseColor(Color.WHITE); // erase the BitMap with white
   }       

   public void load_pic(String picturePath) // load a picture from gallery
   {
      pathMap.clear(); // remove all paths
      previousPointMap.clear(); // remove all previous points
      bitmap = BitmapFactory.decodeFile(picturePath);
      invalidate(); // refresh the screen
   }   

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

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

      // determine which type of action the given MotionEvent represents, then call the corresponding handling method
      if (action == MotionEvent.ACTION_DOWN || action == MotionEvent.ACTION_POINTER_DOWN) 
      {
         touchStarted(event.getX(actionIndex), event.getY(actionIndex), event.getPointerId(actionIndex));
      } // end if
      else if (action == MotionEvent.ACTION_UP || action == MotionEvent.ACTION_POINTER_UP) 
      {
         touchEnded(event.getPointerId(actionIndex));
      } // end else if
      else 
      {
         touchMoved(event); 
      } // end else

      invalidate(); // redraw
      return true; // consume the touch event
   } // end method onTouchEvent

   // called when the user touches the screen
   private void touchStarted(float x, float y, int lineID) 
   {
      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
      } // end if
      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
      } // end else

      // move to the coordinates of the touch
      path.moveTo(x, y);
      point.x = (int) x;
      point.y = (int) y;
   }

...similar for other on Touch event

Answer 1

Touch事件结束时是否删除了pathMap（即touchEnded方法）？

这会导致您描述的行为，因为您没有在Bitmap上绘图，而是在Canvas上绘制了直线和位图（并且每次onDraw事件都会重绘Canvas））;也就是说，对于每个onDraw，您将绘制上一个绘图。

Answer 2

我使用以下代码解决了这个问题。需要复制位图以进行编辑。

bitmap = (BitmapFactory.decodeFile(picturePath));
bitmap = bitmap.copy(Bitmap.Config.ARGB_8888, true);    
bitmapCanvas = new Canvas(bitmap);
invalidate();

android绘图应用程序：无法在从库中加载的位图上绘制线条

编码：

2 个答案: