来源：https://segmentfault.com/a/1190000007133405

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.text.style.ImageSpan;
import java.lang.ref.WeakReference;

/**
 * 图片垂直居中显示
 * Created by liuguoquan on 16/9/5.
 */
public class CenterImageSpan extends ImageSpan {

  private WeakReference<Drawable> mDrawableRef;

  public CenterImageSpan(Context context, int resourceId, int verticalAlignment) {
    super(context, resourceId, verticalAlignment);
  }

  @Override public int getSize(Paint paint, CharSequence text, int start, int end,
      Paint.FontMetricsInt fontMetricsInt) {
    Drawable drawable = getDrawable();
    Rect rect = drawable.getBounds();
    if (fontMetricsInt != null) {
      Paint.FontMetricsInt fmPaint = paint.getFontMetricsInt();
      int fontHeight = fmPaint.descent - fmPaint.ascent;
      int drHeight = rect.bottom - rect.top;
      int centerY = fmPaint.ascent + fontHeight / 2;

      fontMetricsInt.ascent = centerY - drHeight / 2;
      fontMetricsInt.top = fontMetricsInt.ascent;
      fontMetricsInt.bottom = centerY + drHeight / 2;
      fontMetricsInt.descent = fontMetricsInt.bottom;
    }
    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 drawable = getCachedDrawable();
    canvas.save();
    Paint.FontMetricsInt fmPaint = paint.getFontMetricsInt();
    int fontHeight = fmPaint.descent - fmPaint.ascent;
    int centerY = y + fmPaint.descent - fontHeight / 2;
    int transY = centerY - (drawable.getBounds().bottom - drawable.getBounds().top) / 2;
    canvas.translate(x, transY);
    drawable.draw(canvas);
    canvas.restore();
  }

  private Drawable getCachedDrawable() {
    WeakReference<Drawable> wr = mDrawableRef;
    Drawable d = null;
    if (wr != null) {
      d = wr.get();
    }

    if (d == null) {
      d = getDrawable();
      mDrawableRef = new WeakReference<>(d);
    }

    return d;
  }
}

// 评论内容，设置标签、链接跳转
Spannable content = new SpannableStringBuilder("占位  " + comment.getContent());
CenterImageSpan span = new CenterImageSpan(mActivity,R.drawable.ic_btn_ask,ImageSpan.ALIGN_BASELINE);
// 用ImageSpan替换文本
content.setSpan(span, 0, 2, Spannable.SPAN_INCLUSIVE_EXCLUSIVE);
holder.mAskText.setText(content);