title: JavaFX lookup issues with ScrollPane and TitledPane
body: <p>I have a Scene called modSelectorScene, based on an fxml made in Scene Builder, the root element of which is a ScrollPane. The ScrollPane contains a VBox, which contains a few TitledPanes, each of which contains an AnchorPane, each of which contains a few Buttons.</p>
  
  <p>The trouble all started when I tried to use modSelectorScene.lookup() with each button's fx:id to assign the buttons to Button objects in my code - each one was turning up null. I found I could assign an fx:id to the ScrollPane and lookup that, but nothing else. If I wrap the ScrollPane in, say, an AnchorPane and move one of the buttons into the AnchorPane, I can get at it normally with the lookup method.</p>
  
  <p>So the solution I'm looking at right now involves alternating calls of getContent() and getChildren() on the ScrollPane and everything inside it to dig my way down and get my buttons that way. That works, but it's not very...elegant. So what I'd like to know is why the Buttons and all the other elements are somehow invisible to the lookup method while they're behind that ScrollPane, and whether there's any way to remedy that.</p>
  
  <p>Here's one example:</p>
  
  <pre><code>modSelectorScene = new Scene(FXMLLoader.load(getClass().getResource("Dialog/ModSelector.fxml")));
  ...
  ScrollPane modScrollPane = (ScrollPane) modSelectorScene.lookup("#modScrollPane");
  Button modStr = (Button) modSelectorScene.lookup("#modStr");
  </code></pre>
  
  <p>Trying to add an EventHandler to modStr, for instance, throws a NullPointerException, but the ScrollPane is assigned as expected. Even the VBox directly inside it returns a null on lookup.</p>