title: How to disable hiding of combobox popup in JavaFX8?
body: <p>Is there a way to constantly show combobox popup? The question was about datepicker, but it is a descendant of combobox. I want to call show() method of combobox and then constantly show it until stage is closed.
  The best thing that it got till now is</p>
  
  <pre><code>    showingProperty().addListener({ ov, old, newValue -&gt;
          if (!newValue) this.show()
      })
  </code></pre>
  
  <p>It kinda works, but it hides popup and then shows it, and that is inconvinient.</p>