You cannot add items to combobox through SceneBuilder. Either you can add through the FXML file, like you, or through the controller, as shown below.
@Override public void initialize(URL location, ResourceBundle resources) { comboBox.getItems().removeAll(comboBox.getItems()); comboBox.getItems().addAll("Option A", "Option B", "Option C"); comboBox.getSelectionModel().select("Option B"); }
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