Question

我是Java新手，有一点问题。

有两个类，我试图从PopupCarEntryController类写入ChoiceCarController类中的 ArrayList 。使用addCarToList方法。

但每次启动此方法时，ArrayList都为空或被覆盖。

ChoiceCarController：

import Car;
import java.net.URL;
import java.util.ResourceBundle;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Button;
import javafx.scene.control.ChoiceBox;
import javafx.scene.control.ComboBox;
import javafx.scene.control.Label;
import javafx.scene.control.Separator;

public class FXMLChoiceCarController implements Initializable {

    private FahrtenbuchFX application;

    public FXMLChoiceCarController() {
        this.carChoiceBox = new ChoiceBox(carChoiceBoxData);
    }

    @FXML
    private void handleSelectButtonAction(ActionEvent event) {
        if (!carChoiceBox.getSelectionModel().isEmpty()) {
            application.FahrtenbuchView();
        } else {

        }
    }

    @FXML
    private void handleAddButtonAction(ActionEvent event) {
        application.showPopup();
    }

    @FXML
    private void handleExitButtonAction(ActionEvent event) {
        System.exit(0);
    }


    public ObservableList<Car> carChoiceBoxData = FXCollections.observableArrayList();

    @FXML
    private ChoiceBox carChoiceBox;

    @FXML
    private void handleCarChoiceBoxAction(ActionEvent event) {

    }

    @Override
    public void initialize(URL url, ResourceBundle rb) {
        carChoiceBox.getSelectionModel().selectFirst();
        carChoiceBox.setItems(carChoiceBoxData);
//        this.carChoiceBoxData.add(new Car("asdf", "asdf"));
        System.out.println(getCarList());
    }

    public void addCarToList(Car car) {
        System.out.println(getCarList());
        carChoiceBoxData.add(car);
        System.out.println(getCarList());
    }

    public String getCarList() {
        return carChoiceBoxData.toString();
    }

    public void setApp(FahrtenbuchFX application) {
        this.application = application;
    }

}

和PopupCarEntryController

import Car;
import java.net.URL;
import java.util.ResourceBundle;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Button;
import javafx.scene.control.ChoiceBox;
import javafx.scene.control.ComboBox;
import javafx.scene.control.Label;
import javafx.scene.control.Separator;
import javafx.scene.control.TextField;


public class FXMLPopupCarEntryController implements Initializable {

    private FahrtenbuchFX application;

    @FXML
    private Label labelErrorMessage;

    @FXML
    private TextField textFieldProducer;

    @FXML
    private TextField textFieldModel;

    @FXML
    private TextField textFieldEngine;

    @FXML
    private TextField textFieldFuel;

    @FXML
    private TextField textFieldFlag;

    @FXML
    private void handleSaveButtonAction(ActionEvent event) {
        FXMLChoiceCarController carController = new FXMLChoiceCarController();
        carController.addCarToList(new Car(textFieldProducer.getText(), textFieldModel.getText()));

    }

    @FXML
    private void handleCloseButtonAction(ActionEvent event) {
        application.hidePopup();
    }

    @Override
    public void initialize(URL url, ResourceBundle rb) {
        //TODO
    }

    public void setApp(FahrtenbuchFX application) {
        this.application = application;
    }
}

我不理解的是，当我在void initialize方法中初始化List并在addCarToList方法中执行 out.println 时，结果是不同的。就像变量指向不同的ArrayList一样。

Answer 1

那是因为每次你像这样实例化控制器类：

FXMLChoiceCarController carController = new FXMLChoiceCarController();

所以你每次都在创建列表，如：

public ObservableList<Car> carChoiceBoxData = FXCollections.observableArrayList();

如果您想重复使用列表，请将列表设为静态，如：

public static ObservableList<Car> carChoiceBoxData = FXCollections.observableArrayList();

所以你只有一个列表实例。

JavaFX observableArrayList总是被覆盖

1 个答案: