Android：暂时返回错误的触摸指针ID

Question

我正在使用以下代码为android创建一个多边形列表供以后重绘。 问题是由于某种原因，当一个手指被按住而另一个手指被按到屏幕时，返回的指针ID是0。但是，当一个或多个手指同时按下屏幕时，会生成正确的Id。

public boolean onTouchEvent(MotionEvent e) {
    //Cycle through all pointer indexes
    for(int i=0; i < e.getPointerCount(); i++){
        int PointerId=e.getPointerId(i);                    //Get the pointer Id for that index.
        int x= (int)e.getX(e.findPointerIndex(PointerId));  //Get the x coordinate for the current pointer id.
        int y= (int)e.getY(e.findPointerIndex(PointerId));  //Get the y coordinate for the current pointer id.
            //Handle Touch events.
            switch(e.getActionMasked()){
                case MotionEvent.ACTION_POINTER_DOWN:           //Check for subsequent Pointer down events.
                case MotionEvent.ACTION_DOWN:{                  //Check for first finger down.  
                    pntsU.put(PointerId,new Polygon(x,y,Color));//Create a new polygon finger down event, and associate with the Pointer Id.
                    Log.i("Pointer Id: ","" + PointerId);       //Log the pointer id for testing.
                    break;
                }
                case MotionEvent.ACTION_MOVE:{                  //A finger move event has occured.
                    pntsU.get(PointerId).Points.add(new Point(x,y));//Add a point to the Associated polygon.
                    break;
                }
                case MotionEvent.ACTION_POINTER_UP:             //A finger has been lifted.
                case MotionEvent.ACTION_UP:{
                    pntsCommited.add(pntsU.get(PointerId));     //Store the associated polygon in a permanent list.
                    break;
                }
            }

    }
    invalidate();
    return true;
}

编辑：对于任何关心或有此问题的人，我已经解决了。 这是我更新的代码。

    public boolean onTouchEvent(MotionEvent e) {
    int x,y;
    int PointerId,PointerIndex;
        //Handle Touch events.
        switch(e.getActionMasked()){
            case MotionEvent.ACTION_POINTER_DOWN:                       //Check for subsequent Pointer down events.
            case MotionEvent.ACTION_DOWN:{                              //Check for first finger down.
                PointerIndex = (e.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
                PointerId= e.getPointerId(PointerIndex);
                x= (int) e.getX(PointerIndex);
                y= (int) e.getY(PointerIndex);
                pntsU.put(PointerId,new Polygon(x,y,Color));            //Create a new polygon finger down event, and associate with the Pointer Id.
                break;
            }
            case MotionEvent.ACTION_MOVE:{                              //A finger move event has occurred.
                //Cycle through all pointer indexes
                for(int i=0; i < e.getPointerCount(); i++){
                    PointerId=e.getPointerId(i);                        //Get the pointer Id for that index.
                    x= (int)e.getX(e.findPointerIndex(PointerId));      //Get the x coordinate for the current pointer id.
                    y= (int)e.getY(e.findPointerIndex(PointerId));      //Get the y coordinate for the current pointer id.
                    x=Math.max(x,0);                                    //Enforce x and y boundaries.
                    x=Math.min(x,getWidth());
                    y=Math.max(y,0);
                    y=Math.min(y,getHeight());
                    pntsU.get(PointerId).Points.add(new Point(x,y));    //Add a point to the Associated polygon.
                }
                break;
            }
            case MotionEvent.ACTION_POINTER_UP:                         //A finger has been lifted.
            case MotionEvent.ACTION_UP:{
                PointerIndex = (e.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
                PointerId= e.getPointerId(PointerIndex);
                pntsCommited.add(pntsU.get(PointerId));                 //Store the associated polygon in a permanent list.
                break;
            }
        }
    invalidate();
    return true;
}

请注意，我已将for循环代码移动到修复问题的Action_Move部分。我不确定为什么会这样，但我的猜测是它可能与Action_Move事件总是返回指针Id为0的事实有关，因此在某些情况下导致第二次点击返回0。强制在Action_Move中循环指针索引将解决此问题，并确保您获得正确的指针Id。