不要在canvas android上使用drawString覆盖字符串

Question

我在imageview上写了一个字符串。现在，当在imageview上触摸手指时，前一个字符串将被覆盖。每次在imageview中的不同位置触摸手指时，我都不会覆盖前一个字符串。我怎么能做到这一点。谢谢

imageview.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {


 switch (action) {
                case MotionEvent.ACTION_DOWN:


                    Bitmap.Config config = bm.getConfig();
                    int width = bm.getWidth();
                    int height = bm.getHeight();

                    bm2 = Bitmap.createBitmap(width, height, config);

                    c = new Canvas(bm2);
                    c.drawBitmap(bm, 0, 0, null);

                    paint = new Paint();
                    paint.setTextSize("14");
                    paint.setColor(Color.RED);
                    paint.setTypeface(TYPEFACE.NORMAL);

                   c.drawText(words, x, y, paint);
                    imageview.setImageBitmap(bm2);


                    break;


 case MotionEvent.ACTION_UP:
                    break;

            }


            return true;