How to fix it
Remove the line countChoiceBox = new ChoiceBox();
and everything will work fine, assuming you have no other bugs elsewhere in your application.
The program will use the reference to the countChoiceBox which is part of the node hierarchy created by the FXMLLoader and set in your scene.
What is happening
Loading a new FXML in onChangeCountClick
will:
- Create a new
supermarket.ManageWindowCC
controller. - Create a hierarchy of Nodes based upon the FXML definition.
- One of the nodes in the hierarchy will be a ChoiceBox.
- The ChoiceBox which the FXML loader automatically creates for you will be assigned to the countChoiceBox member.
- You then take the hierarchy of nodes assigned to root and add it to your new Scene on your new Stage.
So, after you load the FXML, countChoiceBox is initialized to an empty ChoiceBox instantiated by your FXMLLoader
This is all fine so far . . .
What you then do is (incorrectly) write:
countChoiceBox = new ChoiceBox();
The rule of thumb you violate is => never use new
to assign a value to a members tagged @FXML
.
Also see the somewhat related example for populating a ComboBox using FXML (though that sample uses a ComboBox and populates its data directly in FXML, so it is not directly applicable to your situation).