即使添加元素后ComboBox也为空

Question

我创建了一个ComboBox并向其中添加了元素，但是它始终显示为空白。我在这里做错了什么？预先感谢！

我的FXML文件：

<GridPane fx:id="gridEdits"
              style="-fx-padding: 10 10 10 10" hgap="10" vgap="10">
        <Label GridPane.columnIndex="0" GridPane.rowIndex="0">
            Starting Time After: </Label>
        <TextField GridPane.columnIndex="1" GridPane.rowIndex="0"
                   fx:id="tfShowingID" editable="false"/>

        <Label GridPane.columnIndex="0" GridPane.rowIndex="1">
            Ending Time Before:</Label>
        <TextField GridPane.columnIndex="1" GridPane.rowIndex="1"
                   fx:id="tfVenue" editable="false"/>

        <Label GridPane.columnIndex="0" GridPane.rowIndex="2">
            Advisory Rating:</Label>
        <SearchableComboBox GridPane.columnIndex="1" GridPane.rowIndex="2"
                            fx:id="selector" editable="true"/> </GridPane>

在我的Java文件中：

public SearchableComboBox<String> selector;   
ObservableList<String> data = FXCollections.observableArrayList("14 Accompaniment (14A)", "18 
ccompaniment (18A)","General (G)", "Parent Guidance (PG)", "Restricted (R)", "Unrated (U)");
selector = new SearchableComboBox<>(data);