java JavaFX | ChoiceBox

JavaFX | ChoiceBox

原文:https://www.geeksforgeeks.org/javafx-choicebox/

ChoiceBox 是 JavaFX 包的一部分。ChoiceBox 显示一组项目，并允许用户选择一个选项，它将在顶部显示当前选择的项目。除非另外选择，否则默认情况下，选项框没有选定的项目。可以先指定项目，然后指定选定项目，也可以先指定选定项目，然后指定项目。

choice box 类的构造函数为:

ChoiceBox() :新建一个空的 ChoiceBox。
选择盒子(可观察的列表项目):用给定的一组项目创建一个新的选择盒子。

常用方法:

方法	说明
【getitem()	获取属性项的值。
getValue（）	获取属性值。
隐藏()	关闭选项列表。
设置项目(观察列表值)	设置属性项的值。
设定值(T 值)	设置属性值。
显示()	打开选项列表。

下面的程序说明了 ChoiceBox 的使用:

Program to create a ChoiceBox and add items to it: This program creates a ChoiceBox named c and add a list of string to it using(ChoiceBox(FXCollections.observableArrayList(string_array))). We would add the choice and a label to the tilepane(getChildren().add() function). Then we will create a stage (container) and add the tilepane to the scene and add the scene to the stage. Then display the stage using show() function.

```java // Java Program to create a ChoiceBox and add items to it. import javafx.application.Application; import javafx.scene.Scene; import javafx.scene.control.; import javafx.scene.layout.; import javafx.event.ActionEvent; import javafx.event.EventHandler; import javafx.collections.*; import javafx.stage.Stage; public class Choice_1 extends Application {

// launch the application     public void start(Stage s)     {         // set title for the stage         s.setTitle("creating ChoiceBox");

// create a button         Button b = new Button("show");

// create a tile pane         TilePane r = new TilePane();

// create a label         Label l = new Label("This is a choice box");

// string array         String st[] = { "Arnab", "Andrew", "Ankit", "None" };

// create a choiceBox         ChoiceBox c = new ChoiceBox(FXCollections.observableArrayList(st));

// add ChoiceBox         r.getChildren().add(l);         r.getChildren().add(c);

// create a scene         Scene sc = new Scene(r, 200, 200);

// set the scene         s.setScene(sc);

s.show();     }

public static void main(String args[])     {         // launch the application         launch(args);     } } ```

输出 :
Program to create a ChoiceBox and add listener to it: This program creates a ChoiceBox named c and add a list of string to it using(ChoiceBox(FXCollections.observableArrayList(string_array))). We would add a change listener to detect when the user selects an item of the choice (we will add the listener using addListener() function ). The change listener has a function(public void changed(ObservableValue ov, Number value, Number new_value)) which is invoked when the selection of choice is changed. We would add the choice and a label to the tilepane(getChildren().add() function). Then we will create a stage (container) and add the tilepane to the scene and add the scene to the stage. Finally, display the stage using show() function.

```java // Java Program to create a ChoiceBox and add listener to it. import javafx.application.Application; import javafx.scene.Scene; import javafx.scene.control.; import javafx.scene.layout.; import javafx.event.ActionEvent; import javafx.event.EventHandler; import javafx.collections.; import javafx.beans.value.; import javafx.stage.Stage; public class Choice_2 extends Application {

// launch the application     public void start(Stage s)     {         // set title for the stage         s.setTitle("creating ChoiceBox");

// create a button         Button b = new Button("show");

// create a tile pane         TilePane r = new TilePane();

// create a label         Label l = new Label("This is a choice box");         Label l1 = new Label("nothing selected");

// string array         String st[] = { "Arnab", "Andrew", "Ankit", "None" };

// create a choiceBox         ChoiceBox c = new ChoiceBox(FXCollections.observableArrayList(st));

// add a listener         c.getSelectionModel().selectedIndexProperty().addListener(new ChangeListener() {

// if the item of the list is changed             public void changed(ObservableValue ov, Number value, Number new_value)             {

// set the text for the label to the selected item                 l1.setText(st[new_value.intValue()] + " selected");             }         });

// add ChoiceBox         r.getChildren().add(l);         r.getChildren().add(c);         r.getChildren().add(l1);

// create a scene         Scene sc = new Scene(r, 200, 200);

// set the scene         s.setScene(sc);

s.show();     }

public static void main(String args[])     {         // launch the application         launch(args);     } } ```

输出 :