ChoiceBox（选择框）

JavaFX ChoiceBox 控件使用户能够从预定义的选项列表中选择一个选项。JavaFX ChoiceBox 控件由 javafx.scene.control.ChoiceBox 类表示。这个 JavaFX ChoiceBox 教程将解释如何使用 ChoiceBox 类。

The JavaFX ChoiceBox control enables users to choose an option from a predefined list of choices. The JavaFX ChoiceBox control is represented by the class javafx.scene.control.ChoiceBox . This JavaFX ChoiceBox tutorial will explain how to use the ChoiceBox class.

创建一个 ChoiceBox

您只需通过创建 ChoiceBox 类的新实例来创建 ChoiceBox。这是一个 JavaFX ChoiceBox 实例化的示例：

You create a ChoiceBox simply by creating a new instance of the ChoiceBox class. Here is a JavaFX ChoiceBox instantiation example:

ChoiceBox choiceBox = new ChoiceBox();

将选项添加到 ChoiceBox

您可以通过获取其选项集合并向其添加项目来将选项添加到 ChoiceBox。这是一个向 JavaFX ChoiceBox 添加选项的示例：

You can add choices to a ChoiceBox by obtaining its item collection and add items to it. Here is an example that adds choices to a JavaFX ChoiceBox:

choiceBox.getItems().add("Choice 1");
choiceBox.getItems().add("Choice 2");
choiceBox.getItems().add("Choice 3");

向场景图中添加 ChoiceBox

要使 ChoiceBox 可见，您必须将其添加到场景图中。这意味着您必须将 ChoiceBox 添加到 Scene 对象或某些布局组件，然后将其附加到 Scene 对象。

To make a ChoiceBox visible you must add it to the scene graph. This means that you must add the ChoiceBox to a Scene object or to some layout component which is then attached to the Scene object.

下面是一个示例，展示了如何将 JavaFX ChoiceBox 添加到场景图中：

Here is an example showing how to add a JavaFX ChoiceBox to the scene graph:

package com.jenkov.javafx.controls;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ChoiceBox;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;
public class ChoiceBoxExperiments extends Application  {
    @Override
    public void start(Stage primaryStage) throws Exception {
        primaryStage.setTitle("ChoiceBox Experiment 1");
        ChoiceBox choiceBox = new ChoiceBox();
        choiceBox.getItems().add("Choice 1");
        choiceBox.getItems().add("Choice 2");
        choiceBox.getItems().add("Choice 3");
        HBox hbox = new HBox(choiceBox);
        Scene scene = new Scene(hbox, 200, 100);
        primaryStage.setScene(scene);
        primaryStage.show();
    }
    public static void main(String[] args) {
        Application.launch(args);
    }
}

运行此示例生成的应用程序将类似于以下内容：

The application resulting from running this example would look similar to this:

读取选定的值

您可以通过 getValue() 方法读取 ChoiceBox 的选定值。如果未选择任何选项，则 getValue() 方法将返回 null。以下是调用 getValue() 的示例：

You can read the selected value of a ChoiceBox via its getValue() method. If no choice is selected, the getValue() method returns null. Here is an example of calling getValue():

String value = (String) choiceBox.getValue();

侦听选择

可以通过其 setOnAction() 方法在 ChoiceBox 上设置一个动作侦听器来侦听 JavaFX ChoiceBox 中选择的更改。下面是在 ChoiceBox 上设置动作侦听器的示例，该侦听器读取在 ChoiceBox 中选择的值：

It is possible to listen for selection changes in a JavaFX ChoiceBox by setting an action listener on the ChoiceBox via its setOnAction() method. Here is an example of setting an action listener on a ChoiceBox which reads what value was selected in the ChoiceBox:

ChoiceBox choiceBox = new ChoiceBox();
choiceBox.getItems().add("Choice 1");
choiceBox.getItems().add("Choice 2");
choiceBox.getItems().add("Choice 3");
choiceBox.setOnAction((event) -> {
    int selectedIndex = choiceBox.getSelectionModel().getSelectedIndex();
    Object selectedItem = choiceBox.getSelectionModel().getSelectedItem();
    System.out.println("Selection made: [" + selectedIndex + "] " + selectedItem);
    System.out.println("   ChoiceBox.getValue(): " + choiceBox.getValue());
});