自定义ImageSpan

    /**
     * span图片垂直居中
     */
    public class VerticalImageSpan extends ImageSpan {

        @SuppressWarnings("unused")
        public VerticalImageSpan(Context arg0, int arg1) {
            super(arg0, arg1);
        }

        public VerticalImageSpan(Context context, Bitmap b) {
            super(context, b, ALIGN_BASELINE);
        }

        public int getSize(Paint paint, CharSequence text, int start, int end,
                           Paint.FontMetricsInt fm) {
            Drawable d = getDrawable();
            Rect rect = d.getBounds();
            if (fm != null) {
                Paint.FontMetricsInt fmPaint = paint.getFontMetricsInt();
                int fontHeight = fmPaint.bottom - fmPaint.top;
                int drHeight = rect.bottom - rect.top;

                int top = drHeight / 2 - fontHeight / 4;
                int bottom = drHeight / 2 + fontHeight / 4;

                fm.ascent = -bottom;
                fm.top = -bottom;
                fm.bottom = top;
                fm.descent = top;
            }
            return rect.right;
        }

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