How to update JavaFX binding reference of an Object

Question

Consider the following models, Apple

public class Apple { private StringProperty appleName = new SimpleStringProperty("Apple"); public String getAppleName() { return appleName.get(); } public StringProperty appleNameProperty() { return appleName; } public void setAppleName(String appleName) { this.appleName.set(appleName); } }

and Basket

public class Basket { private Apple apple = new Apple(); public Apple getApple() { return apple; } public void setApple(Apple apple) { this.apple = apple; } }

Basket has an apple. Now I'm trying to bind a simple string property as below.

public class Food{ public static void main(String[] args) { StringProperty localApple = new SimpleStringProperty("lGreenApple"); Basket basket = new Basket(); Apple rGreenApple = new Apple(); rGreenApple.setAppleName("rGreenApple"); basket.setApple(rGreenApple); Bindings.bindBidirectional(localApple, rGreenApple.appleNameProperty()); rGreenApple.appleNameProperty().set("rGreenApple 2"); System.out.println(localApple.getValue()); //rGreenApple 2 Apple redApple = new Apple(); redApple.setAppleName("rRedApple"); basket.setApple(redApple); redApple.appleNameProperty().set("rRedApple 2"); System.out.println(localApple.getValue());//Still rGreenApple 2 } }

While trying to retrieve value after binding, still localApple object has reference to rGreenApple. What is the clean way to get the red apple?

James_D · Accepted Answer · 2015-04-06 15:12:48Z

You need two things:

Make the apple property in Basket a JavaFX observable property, instead of a regular JavaBean-style property.
Bind the local string property to a "property of a property", i.e. the appleName property of the apple property of the Basket.

The first part is easy:

public class Basket { private final ObjectProperty<Apple> apple = new SimpleObjectProperty<>(); public ObjectProperty<Apple> appleProperty() { return apple ; } public final Apple getApple() { return appleProperty().get(); } public final void setApple(Apple apple) { appleProperty().set(apple); } }

For the second part, the cleanest way is to use the EasyBind framework:

public class Food{ public static void main(String[] args) { Basket basket = new Basket(); Apple rGreenApple = new Apple(); rGreenApple.setAppleName("rGreenApple"); basket.setApple(rGreenApple); Property<String> localApple = EasyBind.monadic(basket.appleProperty()) .selectProperty(Apple::appleNameProperty); rGreenApple.appleNameProperty().set("rGreenApple 2"); System.out.println(localApple.getValue()); //rGreenApple 2 Apple redApple = new Apple(); redApple.setAppleName("rRedApple"); basket.setApple(redApple); System.out.println(localApple.getValue());// rRedApple redApple.appleNameProperty().set("rRedApple 2"); System.out.println(localApple.getValue());// rRedApple 2 } }

Without EasyBind, you have to manage the intermediate listeners by hand. Something like:

 StringProperty localApple = new SimpleStringProperty(); localApple.bindBidirectional(basket.getApple().appleNameProperty()); basket.appleProperty().addListener((obs, oldApple, newApple) -> { if (oldApple != null) { localApple.unbindBidirectional(oldApple.appleNameProperty()); } if (newApple == null) { localApple.set(""); } else { localApple.bindBidirectional(newApple.appleNameProperty()); } });

Not easily... You'd basically just end up replicating the relevant parts of the framework code.
Added a way to do this without EasyBind. If you have a longer chain of properties, it gets pretty ugly.
Tried both. Though it's EasyBind is nice, I'll go with listener for approach to know more. Much thanks.

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