Android ImageSpan与TextView同一行图片居中

 public static class FontMetrics {
        /**
         * The maximum distance above the baseline for the tallest glyph in
         * the font at a given text size.
         */
        public float   top;//最高字符到baseline的值，即ascent的最大值
        /**
         * The recommended distance above the baseline for singled spaced text.
         */
        public float   ascent;//系统建议的，绘制单个字符时，baseline至字符最高处的距离
        /**
         * The recommended distance below the baseline for singled spaced text.
         */
        public float   descent;//系统建议的，绘制单个字符时，baseline至字符最低处的距离
        /**
         * The maximum distance below the baseline for the lowest glyph in
         * the font at a given text size.
         */
        public float   bottom;//最低字符到baseline的值
        /**
         * The recommended additional space to add between lines of text.
         */
        public float   leading;//上一行字符的descent到下一行字符ascent之间的距离，行间距
    }

 @Override
    public void draw(Canvas canvas, CharSequence text, int start, int end, float x, int top, int y, int bottom, Paint paint) {
        Drawable drawable = getDrawable();
        Paint.FontMetricsInt fontMetricsInt = paint.getFontMetricsInt();
        int transY = (y + fontMetricsInt.descent + y + fontMetricsInt.ascent) / 2 - drawable.getBounds().bottom/2;
        canvas.save();
        canvas.translate(x,transY);
        drawable.draw(canvas);
        canvas.restore();
    }