android中listview滑动的时候卡

具体代码如下，大家帮忙看看 getView方法有什么问题吗？为什么滑动会卡private class ViewHolder{ ImageView iv_thumbnail; TextView tv_filename; TextView tv_filesize; } private ViewHolder viewHolder = null; @Override public View getView(int position, View convertView, ViewGroup parent) { //如果convertView为空，从布局解压缩器中解压缩行布局 if (convertView == null) { viewHolder = new ViewHolder(); convertView = inflater.inflate(R.layout.item_main_list, null); viewHolder.iv_thumbnail = (ImageView) convertView.findViewById(R.id.iv_thumbnail); viewHolder.tv_filename = (TextView) convertView.findViewById(R.id.tv_filename); viewHolder.tv_filesize = (TextView) convertView.findViewById(R.id.tv_filesize); convertView.setTag(viewHolder); } else { viewHolder = (ViewHolder) convertView.getTag(); } //为布局视图设置内容 File video = files.get(position); viewHolder.iv_thumbnail.setImageBitmap(ThumbnailUtils.createVideoThumbnail(video.getAbsolutePath(), Thumbnails.MINI_KIND)); viewHolder.tv_filename.setText("片名："+video.getName().substring(0, video.getName().lastIndexOf("."))); DecimalFormat formater = new DecimalFormat("#.00"); viewHolder.tv_filesize.setText("大小："+formater.format(video.length()*1.0/(1024*1024)) + "MB"); return convertView; }