要实现这样的效果：

屏幕快照 2018-04-29 下午2.49.01.png

用UnderlineSpan、Html实现的效果不是很好，决定继承LineBackgroundSpan逐行画线，效果不错。记录下：

/**
 * 自定义的UnderlineSpan，用于给TextView底部画直线
 *
 * 建议在layout里给textView设置includeFontPadding=false，并且设置lineSpacingMultiplier/lineSpacingExtra
 * 和paddingBottom以留出底部空间画线
 */
public class CustomUnderlineSpan implements LineBackgroundSpan {
    private Paint paint;
    private TextView textView;
    private float offsetY;

    /**
     *
     * @param textView 被画线的textview
     * @param color 底部画线的颜色
     * @param lineHeight 画线的高度（像素值）
     * @param offsetY 画线相对于textView行高从上往下的偏移距离（像素值）
     */
    public CustomUnderlineSpan(TextView textView, int color, float lineHeight, float offsetY) {
        paint = new Paint();
        paint.setColor(color);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(lineHeight);
        this.textView = textView;
        this.offsetY = offsetY;
    }

    @Override
    public void drawBackground(Canvas canvas, Paint p, int left, int right, int top, int baseline,
                               int bottom, CharSequence text, int start, int end, int lnum) {
        int lineNum = textView.getLineCount();
        Layout layout = textView.getLayout();
        float y;
        for (int i = 0; i < lineNum; i++) {
            y = layout.getLineTop(i) + offsetY;
            canvas.drawLine(layout.getLineLeft(i), y, layout.getLineRight(i), y, paint);
        }
    }
}

调起来：

SpannableString ss = new SpannableString(text);
ss.setSpan(new CustomUnderlineSpan(binding.title,
                            Color.parseColor("#C7FFE921"),
                            UIUtil.INSTANCE.dipToPixels(8),
                            UIUtil.INSTANCE.dipToPixels(22)),
                    0, intSpannableStringBuilderLength,
                    Spanned.SPAN_INCLUSIVE_INCLUSIVE);
title.setText(ss);