根据这个信号
这是我现在写的
double timeNow = 0;
timeNow = timer.elapsed();
m_intervalSent += _used - m_currentSent;
m_currentSent = _used;
if(timeNow - m_timeInterval > 300)
{
double speed = m_intervalSent * 1000 / (1024 * 1024) / (timeNow - m_timeInterval);
double leftTime = (_total - _used) /(1024 *1024) / speed;
m_intervalSent = 0;
m_timeInterval = timeNow;
}