将值添加到表视图（JavaFx）

Question

我在这个文件中出现了NullPointerException：

Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.reflect.misc.Trampoline.invoke(Unknown Source)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.reflect.misc.MethodUtil.invoke(Unknown Source)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
... 48 more
Caused by: java.lang.NullPointerException
at Controller.RocketController.addItem(RocketController.java:55)
at Controller.SurvayController.acceptButtonClicked(SurvayController.java:45)

以下是可能导致错误的代码部分

RocketController：

    public void addItem(Aims aim)
    {
        ArrayList<Aims> list = new ArrayList();
        list.add(aim);
        ObservableList<Aims> observableList = FXCollections.observableList(list);
        listView.setItems(observableList);
    }

此功能由另一个阶段的按钮触发：

SurvayController：

@FXML
void acceptButtonClicked()
{
    Aims newAim = new Aims(directionField.getText(),comboBox.getSelectionModel().getSelectedItem(),distanceField.getText(),speedField.getText());
    rocketController.addItem(newAim);
    Stage stage=(Stage) speedField.getScene().getWindow();
    stage.close();

}

你知道我为什么会这样做吗？