Slider bindBidirectional - javafx

Question

Hi I'm stuck in situation where to use bidirectional binding for 2 sliders valueProperty
The task is: there's 2 sliders each of them has maximum value 100
But this value is divided between these 2 sliders, for example if you move first slider to value 20 then second slider value must be 80 and vice versa.
I know this should be done with bind bidirectional but how can I bind expression to the property?
slider1.valueProperty().bindBidirectional(slider2.getMax() - slider2.valueProperty()); ???
Any help will be highly appriciated.

Answer 1

You can't do this with bidirectional binding: you need to use two listeners:
slider1.valueProperty().addListener((obs, oldValue, newValue) ->
slider2.setValue(slider2.getMax() - newValue.doubleValue()));
slider2.valueProperty().addListener((obs, oldValue, newValue) ->
slider1.setValue(slider1.getMax() - newValue.doubleValue()));
SSCCE:
import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Slider;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
public class ConverselyBoundSliders extends Application {
#Override
public void start(Stage primaryStage) {
Slider slider1 = new Slider(0, 100, 50);
Slider slider2 = new Slider(0, 100, 50);
slider1.valueProperty().addListener((obs, oldValue, newValue) ->
slider2.setValue(slider2.getMax() - newValue.doubleValue()));
slider2.valueProperty().addListener((obs, oldValue, newValue) ->
slider1.setValue(slider1.getMax() - newValue.doubleValue()));
VBox root = new VBox(5, slider1, slider2);
root.setPadding(new Insets(12));
primaryStage.setScene(new Scene(root));
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
This seems to work just fine without any infinite recursion occurring; however since it involves floating-point arithmetic and comparisons for that to be true, you might want to make sure that rounding errors in the slider.getMax() - newValue.doubleValue() calculation don't end up with each listener calling the other without escaping from the recursion. The following is a bullet-proof way to do it:
import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Slider;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
public class ConverselyBoundSliders extends Application {
#Override
public void start(Stage primaryStage) {
Slider slider1 = new Slider(0, 100, 50);
Slider slider2 = new Slider(0, 100, 50);
new ConverseSliderBinding(slider1, slider2);
VBox root = new VBox(5, slider1, slider2);
root.setPadding(new Insets(12));
primaryStage.setScene(new Scene(root));
primaryStage.show();
}
private static class ConverseSliderBinding {
private ChangeListener<Number> listener1 ;
private ChangeListener<Number> listener2 ;
private final Slider slider1 ;
private final Slider slider2 ;
private boolean adjusting ;
public ConverseSliderBinding(Slider slider1, Slider slider2) {
this.slider1 = slider1 ;
this.slider2 = slider2 ;
listener1 = (obs, oldValue, newValue) -> {
if (adjusting) return ;
adjusting = true ;
slider2.setValue(slider2.getMax() - newValue.doubleValue());
adjusting = false ;
};
listener2 = (obs, oldValue, newValue) -> {
if (adjusting) return ;
adjusting = true ;
slider1.setValue(slider1.getMax() - newValue.doubleValue());
adjusting = false ;
};
slider1.valueProperty().addListener(listener1);
slider2.valueProperty().addListener(listener2);
}
public void dispose() {
slider1.valueProperty().removeListener(listener1);
slider2.valueProperty().removeListener(listener2);
}
}
public static void main(String[] args) {
launch(args);
}
}