Animate splitpane divider

I have a horizontal split pane, and i would like to on button click, change divider position, so that i create sort of "slide" animation.

divider would start at 0 (complete left) and on my click it would open till 0.2, when i click again, it would go back to 0;

now i achived this, i just use

spane.setdividerPositions(0.2);

and divider position changes, but i cant manage to do this slowly i would really like that slide feeling when changing divider position.

Could anyone help me ? all examples i found on google, show some DoubleTransition, but that does not exist anymore in java 8, at least i dont have import for that.

You can call getDividers().get(0) to get the first divider. It has a positionProperty() that you can animate using a timeline:

import javafx.animation.KeyFrame;
import javafx.animation.KeyValue;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.beans.property.BooleanProperty;
import javafx.beans.property.SimpleBooleanProperty;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.SplitPane;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;
import javafx.util.Duration;

public class AnimatedSplitPane extends Application {

    @Override
    public void start(Stage primaryStage) {
        SplitPane splitPane = new SplitPane(new Pane(), new Pane());
        splitPane.setDividerPositions(0);

        BooleanProperty collapsed = new SimpleBooleanProperty();
        collapsed.bind(splitPane.getDividers().get(0).positionProperty().isEqualTo(0, 0.01));

        Button button = new Button();
        button.textProperty().bind(Bindings.when(collapsed).then("Expand").otherwise("Collapse"));

        button.setOnAction(e -> {
            double target = collapsed.get() ? 0.2 : 0.0 ;
            KeyValue keyValue = new KeyValue(splitPane.getDividers().get(0).positionProperty(), target);
            Timeline timeline = new Timeline(new KeyFrame(Duration.millis(500), keyValue));
            timeline.play();
        });

        HBox controls = new HBox(button);
        controls.setAlignment(Pos.CENTER);
        controls.setPadding(new Insets(5));
        BorderPane root = new BorderPane(splitPane);
        root.setBottom(controls);
        Scene scene = new Scene(root, 600, 600);
        primaryStage.setScene(scene);
        primaryStage.show();

    }

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