非同步載入圖片：先返回一個LevelListDrawable，之後載入圖片，獲取到Bitmap之後轉為Drawable，並設定到之前的LevelListDrawable中，更新level。這裡要注意，要重新設定一下Textview的text，不然圖片顯示不出來。

public class HtmlTool {

	public static SpannableStringBuilder fromHtml(String source, final TextView textView){

		textView.setMovementMethod(LinkMovementMethod.getInstance());

		Spanned spanned = Html.fromHtml(source, new Html.ImageGetter() {
			@Override
			public Drawable getDrawable(String source) {
				final LevelListDrawable drawable = new LevelListDrawable();
				Ion.with(TumlodrApp.mContext)
						.load(source)
						.asBitmap()
						.setCallback(new FutureCallback<Bitmap>() {
							@Override
							public void onCompleted(Exception e, Bitmap result) {
								if(result != null) {
									BitmapDrawable bitmapDrawable = new BitmapDrawable(result);
									drawable.addLevel(1, 1, bitmapDrawable);
									drawable.setBounds(0, 0, result.getWidth(), result.getHeight());
									drawable.setLevel(1);
									CharSequence text = textView.getText();
									textView.setText(text);
									textView.refreshDrawableState();
								}
							}
						});
				return drawable;
			}
		}, null);

		SpannableStringBuilder sp = (SpannableStringBuilder) spanned;
		QuoteSpan[] quoteSpans = sp.getSpans(0, sp.length(), QuoteSpan.class);
		for(QuoteSpan quoteSpan : quoteSpans){
			int start = sp.getSpanStart(quoteSpan);
			int end = sp.getSpanEnd(quoteSpan);
			sp.removeSpan(quoteSpan);
			CustomQuoteSpan customQuoteSapan = new CustomQuoteSpan();
			sp.setSpan(customQuoteSapan, start, end, 0);
		}

		return sp;
	}
}