How to add a hover property to button from the javafx controller instead of CSS

Question

Suppose I have a toggle button in JavaFX CSS defined as such.

.btn:hover{
    -fx-background-color: #ffffff;
}

I have several toggle buttons in a FlowPane, but they all need to have different colors that are determined in the controller. How can I change this hover color from the controller instead?

Answer 1

Define a looked-up color in the CSS file:

.root {
    button-hover-color: #ffffff ;
}
.button:hover {
    -fx-background-color: button-hover-color ;
}

Note that the default CSS actually sets the -fx-color property, from which the background is derived. So if you want to set this up so it behaves in the default way without further modification, experiment with

.root {
    button-hover-color: -fx-hover-base ;
}
.button:hover {
    -fx-color: button-hover-color ;
}

And then in your controller class you can just change the looked-up color on the buttons (or on any container to apply that to all buttons in the container):

public class MyController {
    @FXML
    private Button button ;

    public void initialize() {
        button.setStyle("button-hover-color: red ;");
    }
}

Here's a complete example, using the second CSS file above as style.css.

Main.fxml:

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

<?import javafx.scene.layout.VBox?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.Button?>
<?import javafx.geometry.Insets?>

<VBox alignment="CENTER" spacing="20.0" xmlns="http://javafx.com/javafx/8.0.171" xmlns:fx="http://javafx.com/fxml/1" fx:controller="org.jamesd.examples.hover.Controller">
    <Button fx:id="firstButton" text="First"/>
    <Button fx:id="secondButton" text="Second"/>
    <Button fx:id="thirdButton" text="Third"/>
</VBox>

Controller.java:

import javafx.fxml.FXML;
import javafx.scene.control.Button;

public class Controller {

    @FXML
    private Button firstButton ;
    @FXML
    private Button secondButton ;
    @FXML
    private Button thirdButton ;

    public void initialize() {
        firstButton.setStyle("button-hover-color: #7fc97f;");
        secondButton.setStyle("button-hover-color: #beaed4;");
        thirdButton.setStyle("button-hover-color: #fdc086;");
    }
}

and App.java:

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

import java.io.IOException;

public class App extends Application {

    @Override
    public void start(Stage stage) throws IOException {
        Scene scene = new Scene(FXMLLoader.load(getClass().getResource("Main.fxml")), 640, 480);
        scene.getStylesheets().add(getClass().getResource("style.css").toExternalForm());
        stage.setScene(scene);
        stage.show();
    }


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

}

Note you can also configure the buttons directly in the FXML:

<Button fx:id="firstButton" text="First" style="button-hover-color: #7fc97f;"/>

etc.