title: Why emit signal in constructor doesnt work?
body: <p>I want to emit signals in constructor, like this:</p>
  
  <pre><code>VideoStream::VideoStream(QWidget *parent):
      QMainWindow(parent),
      ui(new Ui::VideoStream)
  {
      ui-&gt;setupUi(this);
      ……  //m_deviceIP already intialized here
      emit streamReq(m_deviceIP);//emitting at here
      recentRecordReq();//this function include a emit sentence,too
  }
  </code></pre>
  
  <p>But it doesnt work!
  For test, I add a Button and then move the emit sentence into the slot, it works well:</p>
  
  <pre><code>void VideoStream::on_streamReqBtn_clicked()
  {
      emit streamReq(m_deviceIP);
  }
  </code></pre>
  
  <p>I don't know why.</p>