title: Javafx adding dynamically pane to vbox Duplicate Children error
body: <p>I have a pane with a label, a text field and a combo box inside a VBox in fxml file. Let´s call it tempPane.
  In the same stage I have a button.
  Once the button is pressed I need to add to the VBox a pane exactly the same as tempPane. This is, adding dynamically a pane to the VBOX.
  I am able to add individual controls such as buttons or labels or text fields to the VBox, but I can´t obtain the same results when trying to add this new pane.</p>
  
  <p>Part of the controller code:</p>
  
  <pre><code>@FXML
  private Pane tempPane;
  
  @FXML 
  private Button btnAddNewPane;;
  
  @FXML
  private VBox vBox;
  
  @FXML
  void addNewPane(ActionEvent event) {
  
      ...
          Pane newPane = new Pane();
          newPane = tempPane;
          // New ID is set to the newPane, this String (NewID) should be 
          //different each time button is pressed
          newPane.setId(newID);
          vBox.getChildren().add(newPane);
      ...
  }
  </code></pre>
  
  <p>And the error I´m getting is:</p>
  
  <pre><code>Exception in thread "JavaFX Application Thread" java.lang.IllegalArgumentException: Children: duplicate children added: parent = VBox[id=filterBox]
  at javafx.graphics/javafx.scene.Parent$3.onProposedChange(Parent.java:580)
  at javafx.base/com.sun.javafx.collections.VetoableListDecorator.add(VetoableListDecorator.java:206)
  at com.sener.dbgui.controller.SearchController$1.run(SearchController.java:53)
  at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$9(PlatformImpl.java:418)
  at java.base/java.security.AccessController.doPrivileged(Native Method)
  at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:417)
  at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
  at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
  at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:175)
  at java.base/java.lang.Thread.run(Thread.java:844)
  </code></pre>
  
  <p>So, why am I getting this duplicate children error? I´m changing the newPane ID before adding it to the VBox.</p>