JavaFX应用程序中的ComboBox不显示数据 [英] ComboBox in JavaFX application doesn't show the data

问题描述

我上课了：

public class Element {
    private final IntegerProperty id;
    private final StringProperty name;

    ...constructors...

    public Integer getId() {
        return id.get();
    }

    public void setId(Integer id) {
        this.id.set(id);
    }

    public IntegerProperty idProperty() {
        return id;
    }

    public String getName() {
        return name.get();
    }

    public void setName(String name) {
        this.name.set(name);
    }

    public StringProperty nameProperty() {
        return name;
    } 

    @Override
    public String toString() {
        return name.get();
    }

我尝试在ComboBox中显示这些元素的列表。在我的控制器中，我有：

And I try to display List of those elements in ComboBox. In my controller I have:

@FXML
private ComboBox<Element> combo;

然后我在函数中有以下代码填充其他GUI元素：

And then I have following code in function that fill other GUI elements:

ObservableList<Element> elements = FXCollections.observableArrayList(ElRep.getElements());
combo = new ComboBox<Element>(elements);
combo.getSelectionModel().selectFirst();

我也尝试过：

combo.setItems(elements);

似乎没有任何效果。我得到空的ComboBox。

and nothing seems to work. I get empty ComboBox.

推荐答案

你应该从不初始化带注释的字段 @ FXML ：该注释的关键是该对象是作为加载FXML文件的一部分创建的，并被注入控制器。如果您创建一个新对象，您将不再引用FXML加载器创建的对象（并显示在UI中）：因此您对该对象属性所做的任何更改都不会显示在UI中。

You should never initialize fields annotated @FXML: the point of that annotation is that the object is created as part of loading the FXML file and is injected into the controller. If you create a new object, you will no longer be referencing the object created by the FXML loader (and displayed in the UI): so any changes you make to that object's properties will not appear in the UI.

因此，省略对新ComboBox<>（...）的调用，并使用 combo.setItems（。 ..）（或 combo.getItems（）。setAll（...））初始化现有的组合框：

So omit the call to new ComboBox<>(...) and use combo.setItems(...) (or combo.getItems().setAll(...)) to initialize the existing combo box:

示例控制器：

import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.fxml.FXML;
import javafx.scene.control.ComboBox;

public class Controller {


    @FXML
    private ComboBox<Element> combo ;

    public void initialize() {
        ObservableList<Element> elements = FXCollections.observableArrayList(
            new Element(1, "Element 1"),
            new Element(2, "Element 2")
        );

        combo.setItems(elements);
        combo.getSelectionModel().selectFirst();
    }
}

FXML文件：

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.control.ComboBox?>

<BorderPane xmlns:fx="http://javafx.com/fxml/1" fx:controller="Controller">
    <top>
        <ComboBox fx:id="combo" />
    </top>
</BorderPane>

测试：

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class Test extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception {
        Scene scene = new Scene(FXMLLoader.load(getClass().getResource("sample.fxml")), 400, 400);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

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