title: PyQt4: self.hide() only hide the content
body: <p>I tried to to subclass QMainWindows and make a call to self.hide() when the minimize event was caught. When I pressed the minimize button, it is minimized to taskbar, and when I pressed it at the taskbar so that it appear again on the screen, I found that it is not invisible. Only the content of the QMainWindows is hide and the frame is still there. </p>
  
  <p>Is it what self.hide() supposed to behave?</p>
  
  <p>I want to make it minimize to system tray, but many of the answers I found from this <a href="https://stackoverflow.com/q/758256/248296">question</a> didn't work.</p>
  
  <p><img src="https://i.stack.imgur.com/CnXMp.png" alt="enter image description here"></p>