JavaFX 下拉框

组合框允许用户选择几个选项之一。用户可以滚动到下拉列表。组合框可以是可编辑和不可编辑的。

创建组合框

以下代码将选项列表包装到ObservableList中，然后使用observable列表实例化ComboBox类。

ObservableList<String> options = 
    FXCollections.observableArrayList(
    "1",
    "2",
    "3"
);
ComboBox comboBox = new ComboBox(options);

我们还可以使用空构造函数创建一个组合框，并调用其setItems方法设置数据。

ComboBox comboBox = new ComboBox(options);
comboBox.setItems(options);

向具有新值的项目的组合框中添加更多项目。

comboBox.getItems().addAll(
    "4",
    "5",
    "6"
);

setValue 方法设置在组合框中选择的项目。在调用setValue方法时，即使值不在组合框项目列表中，selectionModel属性的选定项也会更改为此值。

getValue方法返回所选的值。

要限制下拉列表中可见行的数量，请使用以下代码。

comboBox.setVisibleRowCount(3)

可编辑的组合框

setEditable(true)方法使组合框可编辑。使用setPromptText方法，当不执行选择时，我们可以指定显示在组合框编辑区域中的文本。

ComboBox myComboBox = new ComboBox();
myComboBox.getItems().addAll(
    "s@example.com",
    "i@example.com",
    "e@example.com",
    "m@example.com"  
);
myComboBox.setPromptText("Email address");
myComboBox.setEditable(true);        
myComboBox.setOnAction((Event ev) -> {
    address =  myComboBox.getSelectionModel().getSelectedItem().toString();    
});
myComboBox.setValue("s@example.com");

以下代码创建一个简单的可编辑组合框

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.stage.Stage;

public class Main extends Application {
    public static void main(String[] args) {
        launch(args);
    }
    
    @Override
    public void start(Stage stage) {
        Scene scene = new Scene(new Group(), 450, 250);
        
        ComboBox<String> myComboBox = new ComboBox<String>();
        myComboBox.getItems().addAll("A","B","C","D","E");
        myComboBox.setEditable(true);        
        
        Group root = (Group) scene.getRoot();
        root.getChildren().add(myComboBox);
        stage.setScene(scene);
        stage.show();
        
    }
}

组合框单元格

我们可以使用单元格工厂来改变组合框的默认行为或外观。

以下代码创建一个单元格工厂，并将其应用到组合框。

单元格工厂生成ListCell对象。每个单元格与一个组合框项目相关联。

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.scene.control.ListCell;
import javafx.scene.control.ListView;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import javafx.util.Callback;

public class Main extends Application {
    public static void main(String[] args) {
        launch(args);
    }
    @Override
    public void start(Stage stage) {
        Scene scene = new Scene(new Group(), 200, 200);
        ComboBox<String> myComboBox = new ComboBox<String>();
        myComboBox.getItems().addAll("A", "B", "C", "D", "E");
        myComboBox
            .setCellFactory(new Callback<ListView<String>, ListCell<String>>() {
                @Override
                public ListCell<String> call(ListView<String> param) {
                    final ListCell<String> cell = new ListCell<String>() {
                        {
                            super.setPrefWidth(100);
                        }
                        
                        @Override
                        public void updateItem(String item, boolean empty) {
                            super.updateItem(item, empty);
                            if (item != null) {
                                setText(item);
                                if (item.contains("A")) {
                                    setTextFill(Color.RED);
                                } else if (item.contains("B")) {
                                    setTextFill(Color.GREEN);
                                } else {
                                    setTextFill(Color.BLACK);
                                }
                            } else {
                                setText(null);
                            }
                        }
                    };
                    return cell;
                }
            });
        Group root = (Group) scene.getRoot();
        root.getChildren().add(myComboBox);
        stage.setScene(scene);
        stage.show();
    }
}

例1

将值设置为null以清除ComboBox

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.stage.Stage;

public class Main extends Application {
    public static void main(String[] args) {
        launch(args);
    }
    @Override
    public void start(Stage stage) {
        Scene scene = new Scene(new Group(), 450, 250);
        ComboBox<String> myComboBox = new ComboBox<String>();
        myComboBox.getItems().addAll("A","B","C","D","E");
        myComboBox.setValue("A");
        System.out.println(myComboBox.getValue());
        
        myComboBox.setValue(null);
        
        Group root = (Group) scene.getRoot();
        root.getChildren().add(myComboBox);
        stage.setScene(scene);
        stage.show();
    }
}

例2

设置和获取ComboBox的值

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.stage.Stage;

public class Main extends Application {
    public static void main(String[] args) {
        launch(args);
    }
    @Override
    public void start(Stage stage) {
        Scene scene = new Scene(new Group(), 450, 250);
        ComboBox<String> myComboBox = new ComboBox<String>();
        myComboBox.getItems().addAll("A","B","C","D","E");
        myComboBox.setValue("A");
        System.out.println(myComboBox.getValue());
        
        
        Group root = (Group) scene.getRoot();
        root.getChildren().add(myComboBox);
        stage.setScene(scene);
        stage.show();
    }
}

例3

将更改监听器添加到ComboBox valueProperty

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.stage.Stage;

public class Main extends Application {
    public static void main(String[] args) {
        launch(args);
    }
    @Override
    public void start(Stage stage) {
        Scene scene = new Scene(new Group(), 450, 250);
        ComboBox<String> myComboBox = new ComboBox<String>();
        myComboBox.getItems().addAll("A","B","C","D","E");
        myComboBox.setValue("A");
        System.out.println(myComboBox.getValue());
        myComboBox.valueProperty().addListener(new ChangeListener<String>() {
            @Override public void changed(ObservableValue ov, String t, String t1) {
                System.out.println(ov);
                System.out.println(t);
                System.out.println(t1);
            }    
        });
        
        Group root = (Group) scene.getRoot();
        root.getChildren().add(myComboBox);
        stage.setScene(scene);
        stage.show();
    }
}

例4

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.stage.Stage;

public class Main extends Application {
    public static void main(String[] args) {
        launch(args);
    }
    @Override
    public void start(Stage stage) {
        Scene scene = new Scene(new Group(), 450, 250);
        ComboBox<String> myComboBox = new ComboBox<String>();
        myComboBox.getItems().addAll("A","B","C","D","E");
        myComboBox.setEditable(true);
        myComboBox.setPromptText("Email address");
        
        Group root = (Group) scene.getRoot();
        root.getChildren().add(myComboBox);
        stage.setScene(scene);
        stage.show();
    }
}

例5

在ComboBox中显示矩形

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.scene.layout.GridPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

public class Main extends Application {
    public static void main(String[] args) {
        Application.launch(args);
    }
    @Override
    public void start(final Stage primaryStage) {
        Group root = new Group();
        Scene scene = new Scene(root, 400, 300, Color.WHITE);
        
        GridPane gridpane = new GridPane();
        
        ComboBox<Rectangle> cmb = new ComboBox<Rectangle>();
        cmb.getItems().addAll(
            new Rectangle(10, 10, Color.RED), 
            new Rectangle(10, 10, Color.GREEN), 
            new Rectangle(10, 10, Color.BLUE));
        
        gridpane.add(cmb, 2, 0);
        
        root.getChildren().add(gridpane);   
        primaryStage.setScene(scene);
        
        primaryStage.show();
    }
    
}

例6

以下代码显示了如何使用CellFactory显示组合框值。

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.scene.control.ContentDisplay;
import javafx.scene.control.ListCell;
import javafx.scene.control.ListView;
import javafx.scene.layout.GridPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;
import javafx.util.Callback;

public class Main extends Application {
    public static void main(String[] args) {
        Application.launch(args);
    }
    
    @Override
    public void start(final Stage primaryStage) {
        Group root = new Group();
        Scene scene = new Scene(root, 400, 300, Color.WHITE);
        GridPane gridpane = new GridPane();
        ComboBox<Color> cmb = new ComboBox<Color>();
        cmb.getItems().addAll(Color.RED, Color.GREEN, Color.BLUE);
        cmb.setCellFactory(new Callback<ListView<Color>, ListCell<Color>>() {
            @Override
            public ListCell<Color> call(ListView<Color> p) {
                return new ListCell<Color>() {
                    private final Rectangle rectangle;
                    {
                        setContentDisplay(ContentDisplay.GRAPHIC_ONLY);
                        rectangle = new Rectangle(10, 10);
                    }
                    
                    @Override
                    protected void updateItem(Color item, boolean empty) {
                        super.updateItem(item, empty);
                        
                        if (item == null || empty) {
                            setGraphic(null);
                        } else {
                            rectangle.setFill(item);
                            setGraphic(rectangle);
                        }
                    }
                };
            }
        });
        
        gridpane.add(cmb, 2, 0);
        
        root.getChildren().add(gridpane);
        primaryStage.setScene(scene);
        
        primaryStage.show();
    }
    
}