title: Alternative to QButtonGroup that allows no selection?
body: <p>I'm writing a <code>qt</code>-based c++ application.  I have a number of buttons that I want to be mutually exclusive - only one can be toggled at a time.  I generally use a <a href="http://qt-project.org/doc/qt-4.8/qbuttongroup.html" rel="noreferrer">QButtonGroup</a> for this - it provides a nice logical way to manage sets of buttons.  When one gets pressed, the previously-pressed one gets unpressed, which is exactly the behavior I want.</p>
  
  <p>This time, however, I'd like to allow for the group to be entirely unchecked. Unfortunately this seems to be disallowed by <code>QButtonGroup</code>:</p>
  
  <blockquote>
    <p>exclusive : bool</p>
    
    <p>This property holds whether the button group is exclusive.</p>
    
    <p>If this property is true then only one button in the group can be
    checked at any given time. The user can click on any button to check
    it, and that button will replace the existing one as the checked
    button in the group.</p>
    
    <p>In an exclusive group, <strong>the user cannot uncheck the currently checked
    button by clicking on it;</strong> instead, another button in the group must be
    clicked to set the new checked button for that group.</p>
  </blockquote>
  
  <p>There are a number of ways to work around this, of course.  I'm wondering if there's a pre-made alternative to <code>QButtonGroup</code> that allows this behavior, so that 1) I'm not reinventing the wheel and 2) I can stay within idiomatic <code>qt</code> to make project management easier in the future.</p>
  
  <p>Any suggestions?</p>