[SOLVED] Custom combobox, centered text in JavaFX

Custom combobox, centered text in JavaFX

I want to centre align the text in a combobox button cell and make it a default behaviour. I already know how to do that when a combobox Object has been created. How can i implement that method inside of a derived class of combobox ?

box.setButtonCell(new ListCell<String>() {
    @Override
    public void updateItem(String item, boolean empty) {
        super.updateItem(item, empty);
        if (item != null) {
            setText(item);
            setAlignment(Pos.CENTER_RIGHT);
            Insets old = getPadding();
            setPadding(new Insets(old.getTop(), 0, old.getBottom(), 0));
        }
    }
});

Solution

Of course you could move the code (with box replaced with this) to the constructor of your class (or put it in a initializer block).

But why create a subclass when CSS easily allows you to do this:

Add the following style sheet to the scene

.combo-box>.list-cell {
    -fx-alignment: center;
}

If you want to be able to change this behaviour for individual ComboBoxes, you just need add a way to tell centered ComboBoxes apart from others with a css selector, e.g. a class

java code

comboBox.getStyleClass().add("center-aligned");

CSS

.combo-box.center-aligned>.list-cell {
    -fx-alignment: center;
}

Using a pseudoclass would allow you to switch the behavour on and of more easily though. The following code center aligns every item at even indices:

@Override
public void start(Stage primaryStage) {
    ComboBox<String> combo = new ComboBox<>();

    PseudoClass centerAligned = PseudoClass.getPseudoClass("center-aligned");
    combo.pseudoClassStateChanged(centerAligned, true);
    combo.getSelectionModel().selectedIndexProperty().addListener((o, oldValue, newValue)
            -> combo.pseudoClassStateChanged(centerAligned, newValue.intValue() % 2 == 0));

    for (int i = 0; i < 5; i++) {
        combo.getItems().add("item " + i);
    }
    combo.setValue("item 0");
    combo.setMaxWidth(Double.MAX_VALUE);

    VBox root = new VBox(combo);
    root.setFillWidth(true);
    root.setPrefWidth(300);
    Scene scene = new Scene(root);
    scene.getStylesheets().add("style.css");
    primaryStage.setScene(scene);
    primaryStage.show();
}

style.css

.combo-box:center-aligned>.list-cell {
    -fx-alignment: center;
}