How to change TreeView Color in JavaFX programmatically without using css?

Question

I am trying to implement dark mode functionality. For that purpose I need to change the color of treeView to dark grey. The following code is not working.

treeView.setStyle("-fx-background-color:#242424;");

I am not using CSS separately. So solution like the above code will be highly appreciated.

Answer 1

You need to change the background colors of the cells. Doing this in Java code is tricky, because it forces you to use a custom cellFactory on the tree to access the cells. Instead, I recommend using an external style sheet. You can do

.tree-cell {
    -fx-background-color:#242424;
}

By default, the background of a tree cell (and many other controls) is set to a "looked-up color" (essentially a CSS variable) called -fx-background. The text in the tree cell (and again, in many other controls) is set to a color dependent on that value, so it will automatically become a light color if the background is dark (and vice-versa). So it's probably better to do

.tree-cell {
    -fx-background:#242424;
}

In general, for "theming" your application, the default stylesheet modena.css defines all colors in terms of a small collection of looked-up colors. Those colors, and their defaults, are

/* A light grey that is the base color for objects.  Instead of using
 * -fx-base directly, the sections in this file will typically use -fx-color.
 */
-fx-base: #ececec;


/* A very light grey used for the background of windows.  See also
 * -fx-text-background-color, which should be used as the -fx-text-fill
 * value for text painted on top of backgrounds colored with -fx-background.
 */
-fx-background: derive(-fx-base,26.4%);

/* Used for the inside of text boxes, password boxes, lists, trees, and
 * tables.  See also -fx-text-inner-color, which should be used as the
 * -fx-text-fill value for text painted on top of backgrounds colored
 * with -fx-control-inner-background.
 */
-fx-control-inner-background: derive(-fx-base,80%);
/* Version of -fx-control-inner-background for alternative rows */
-fx-control-inner-background-alt: derive(-fx-control-inner-background,-2%);

/* A bright blue for highlighting/accenting objects.  For example: selected
 * text; selected items in menus, lists, trees, and tables; progress bars */
-fx-accent: #0096C9;

/* Default buttons color, this is similar to accent but more subtle */
-fx-default-button: #ABD8ED;

/* A bright blue for the focus indicator of objects. Typically used as the
 * first color in -fx-background-color for the "focused" pseudo-class. Also
 * typically used with insets of -1.4 to provide a glowing effect.
 */
-fx-focus-color: #039ED3;
-fx-faint-focus-color: #039ED322;

So a good strategy for "theming" your entire application is to change the definitions of some of these and apply it to the root of the scene. For example, a "dark mode" might be implemented just with

.root {
  -fx-base: #242424 ;
  -fx-control-inner-background: derive(-fx-base,20%);
  -fx-control-inner-background-alt: derive(-fx-control-inner-background,-10%);
  -fx-accent: #006689;
  -fx-focus-color: #036E83;
  -fx-faint-focus-color: #036E8322;
}

Here's a complete example:

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.stream.IntStream;

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ComboBox;
import javafx.scene.control.Label;
import javafx.scene.control.ListView;
import javafx.scene.control.TextField;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeView;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

/**
 * JavaFX App
 */
public class App extends Application {


    @Override
    public void start(Stage stage) {

        TreeView<String> tree = createRandomTree();
        BorderPane root = new BorderPane(tree);

        HBox controls = new HBox(5,
            new Button("Click"),
            new Label("Choose one:"),
            new ComboBox<>(FXCollections.observableArrayList("One", "Two", "Three")),
            new TextField()
        );
        controls.setAlignment(Pos.CENTER);
        controls.setPadding(new Insets(5));
        root.setTop(controls);

        ListView<String> list = new ListView<>();
        IntStream.range(1, 51).mapToObj(i -> "Item "+i).forEach(list.getItems()::add);
        root.setLeft(list);


        Scene scene = new Scene(root);
        scene.getStylesheets().add(getClass().getResource("darkmode.css").toExternalForm());

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



    private TreeView<String> createRandomTree() {
        Random rng = new Random();
        List<TreeItem<String>> items = new ArrayList<>();
        TreeItem<String> root = new TreeItem<>("Item 1");
        root.setExpanded(true);
        items.add(root);
        TreeView<String> tree = new TreeView<>(root);
        for (int i = 2 ; i <=20 ; i++) {
            TreeItem<String> item = new TreeItem<>("Item "+i);
            item.setExpanded(true);
            items.get(rng.nextInt(items.size())).getChildren().add(item);
            items.add(item);
        }
        return tree ;
    }



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

}

Where darkmode.css is the CSS file above. This gives:

Note that if you really want to do this without an external CSS file, you can just set those inline styles directly on your root node:

Pane root = ... ;

root.setStyle(
        "  -fx-base: #242424 ;\n" + 
        "  -fx-control-inner-background: derive(-fx-base,20%);\n" + 
        "  -fx-control-inner-background-alt: derive(-fx-control-inner-background,-10%);\n" + 
        "  -fx-accent: #006689;\n" + 
        "  -fx-focus-color: #036E83;\n" + 
        "  -fx-faint-focus-color: #036E8322;");

And you could even just set them for a TreeView, which would apply them only to the tree:

TreeView<String> tree = new TreeView<>();

tree.setStyle(
        "  -fx-base: #242424 ;\n" + 
        "  -fx-control-inner-background: derive(-fx-base,20%);\n" + 
        "  -fx-control-inner-background-alt: derive(-fx-control-inner-background,-10%);\n" + 
        "  -fx-accent: #006689;\n" + 
        "  -fx-focus-color: #036E83;\n" + 
        "  -fx-faint-focus-color: #036E8322;");

but generally, using and external style sheet is better in a number of ways.