title: Allow deselection of RadioButton with a ToggleGroup
body: <p>I'm trying to get a group of <code>RadioButton</code>s in JavaFX 8, with the functionality that at most one can be selected, but it is also possible to remove any selection.  </p>
  
  <p>It seems <code>RadioButton</code> supports deselection only as long as it has no <code>ToggleGroup</code> defined. However, if no <code>ToggleGroup</code> is defined more than one <code>RadioButton</code> may be selected.  </p>
  
  <p>I have tried adding a listener to each button's <code>onAction</code> event:  </p>
  
  <pre><code>for (final RadioButton rb : myRadioButtons) {
      rb.setToggleGroup(myToggleGroup);
      rb.setOnAction(event -&gt; {
          if (rb.isSelected()) {
              myToggleGroup.selectToggle(null);
          }
      });
  }
  </code></pre>
  
  <p>However, there are two problems which make this attempt fail - the first is that the <code>selected</code> property seems to be updated before the <code>action</code> event is fired, so the condition is always true, making it impossible to select <em>any</em> button. 
  The second problem is that the <code>action</code> event is not even fired if the button was selected when it was clicked.   </p>
  
  <p>Adding a listener to the <code>mouseClicked</code> event isn't any better, as it also fires only after the selected button was changed. </p>
  
  <p>Is there a straightforward way to achieve a group of <code>RadioButton</code>s with at-most one selected? Or is the only supported option to handle the <code>ToggleGroup</code>'s responsibilities with change listeners etc.? </p>