OnTouchEvent 中仔细选择文本

Question

我写了一个代码来选择文本的一部分，但是我找不到开始和结束的确切点。

我的代码：

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        final int action = event.getAction();

        switch (action) {
        case MotionEvent.ACTION_DOWN:
        {
            lastX = (int) event.getX();
            lastY = (int) event.getY();
            break;
        }
        case MotionEvent.ACTION_UP:
        {
                int currentX = (int) event.getX();
                int currentY = (int) event.getY();
                int xDistance = Math.abs(currentX - lastX);
                int yDistance = Math.abs(currentY - lastY);

            final Spannable WordtoSpan = (Spannable) mText;

                int line = mLayout.getLineForVertical(yDistance);
                int offset = mLayout.getOffsetForHorizontal(line, xDistance);
                WordtoSpan.setSpan(new BackgroundColorSpan(0xFFFFFF00), line,
offset, Spannable.SPAN_INCLUSIVE_EXCLUSIVE);
                txtContent.setText(WordtoSpan);

                break;
        }
        }
    }

请帮助我，我真的需要它。