javafx change css at runtime

Question

Is it possible to change css for a JavaFX application while it is running?

The effect I am looking for is changing skins or themes at the click of a button.

The UI is in an FXML file if that makes any difference.

I have tried

Scene.getStylesheets()
  .add(getClass().getResource(skinFileName).toExternalForm()); 

which has no effect.

thanks

Answer 1

It should have the effect. Try this full demo code:

public class CssThemeDemo extends Application {

    private String theme1Url = getClass().getResource("theme1.css").toExternalForm();
    private String theme2Url = getClass().getResource("theme2.css").toExternalForm();

    @Override
    public void start(Stage primaryStage) {
        StackPane root = new StackPane();
        final Scene scene = new Scene(root, 300, 250);
        System.out.println("scene stylesheets: " + scene.getStylesheets());
        scene.getStylesheets().add(theme1Url);
        System.out.println("scene stylesheets: " + scene.getStylesheets());

        final Button btn = new Button("Load Theme 1");
        btn.getStyleClass().add("buttonStyle");
        btn.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                scene.getStylesheets().remove(theme2Url);
                System.out.println("scene stylesheets on button 1 click: " + scene.getStylesheets());
                if(!scene.getStylesheets().contains(theme1Url)) scene.getStylesheets().add(theme1Url);
                System.out.println("scene stylesheets on button 1 click: " + scene.getStylesheets());
            }
        });

        final Button btn2 = new Button("Load Theme 2");
        btn2.getStyleClass().add("buttonStyle");
        btn2.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                scene.getStylesheets().remove(theme1Url);
                System.out.println("scene stylesheets on button 2 click: " + scene.getStylesheets());
                if(!scene.getStylesheets().contains(theme2Url)) scene.getStylesheets().add(theme2Url);
                System.out.println("scene stylesheets on button 2 click: " + scene.getStylesheets());
            }
        });

        ComboBox<String> comboBox = new ComboBox<String>(FXCollections.observableArrayList("Just", "another", "control"));
        root.getChildren().add(VBoxBuilder.create().spacing(10).children(btn, btn2, comboBox).build());

        primaryStage.setScene(scene);
        primaryStage.show();
    }

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

theme1 css:

.root{
    -fx-font-size: 14pt;
    -fx-font-family: "Tahoma";
    -fx-base: #DFB951;
    -fx-background: #A78732;
    -fx-focus-color: #B6A678;
}

.buttonStyle {
    -fx-text-fill: #006464;
    -fx-background-color: #DFB951;
    -fx-border-radius: 20;
    -fx-background-radius: 20;
    -fx-padding: 5;
}

theme2 css:

.root{
    -fx-font-size: 16pt;
    -fx-font-family: "Courier New";
    -fx-base: rgb(132, 145, 47);
    -fx-background: rgb(225, 228, 203);
}

.buttonStyle {
    -fx-text-fill: red;
    -fx-background-color: lightcyan;
    -fx-border-color: green;
    -fx-border-radius: 5;
    -fx-padding: 3 6 6 6;
}

Note the same named CSS selectors in both theme1 and theme2 css files.