获取BaseAdapter中getView所消耗的时间出错

public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub

    //文艺式 >>
    long start = System.nanoTime();
    ViewHolder viewHolder;
    if(convertView == null){
        viewHolder = new ViewHolder();
        convertView = mInflater.inflate(R.layout.item,null);
        viewHolder.imageView = (ImageView) convertView.findViewById(R.id.iv_image);
        viewHolder.title = (TextView) convertView.findViewById(R.id.tv_title);
        viewHolder.content = (TextView) convertView.findViewById(R.id.tv_content);
        convertView.setTag(viewHolder);
    }else{
        viewHolder = (ViewHolder) convertView.getTag();     
    }
    ItemBean bean = mList.get(position);
    viewHolder.imageView.setImageResource(bean.ItemImageResid);
    viewHolder.title.setText(bean.ItemTitle);       
    viewHolder.content.setText(bean.ItemContent);
    long end = System.nanoTime();
    long dValue = end - start;
    mSumTime += dValue;
    Log.d("xys",String.valueOf(mSumTime));
    return convertView;

    //文艺式 >>
}
class ViewHolder{
    public ImageView imageView;
    public TextView title;
    public TextView content;
}

}

在BaseAdapter适配器中已经加入成员变量private Long mSumTime;没有long start = System.nanoTime();和long end = System.nanoTime();
long dValue = end - start;
mSumTime += dValue;
Log.d("xys",String.valueOf(mSumTime));
系统运行是正常的，加入获取getView方法所消耗的时间

用这个方法：System.currentTimeMillis();开始和结束各调用一次，然后相减。