Implementing custom JavaFx Bindings

Built in Bindings

Probably you know the JavaFx property binding. (If not here is a tutorial). There are several ways to create a binding. The easiest way is to use the bind or bindBidirectional methods of the property you want to bind. For more complex bindings you can use the Bindings class. It provide a lot of special bindings as static methods e.g. ones that calulate number values, concat string properties, bind ObservableLists, ObservableMaps etc., but nothing for BigDecimal...

Here we have certain excamples for that:

Custom implemented Bindings

If the built in bindings do not fit your needs, JavaFx provides base classes, that you can use for custom implemented bindings. You find them in the package javafx.beans.bindings and all their names end with Binding.

There are only two things to do in your subclass of one of the Binding classes:

• Think about on which other properties your new binding is dependand of. Normally this are the properties you calculate your new value of. Use the bind method to add those properties to the dependencies of the new binding in the initializer block (as done in the examples below) or in the constructor. If the value of one of those changes, the binding value is newly calculated.
• Implement the computeValue method, which returns the new value of the binding.

Normally you think of numbers to compute a value. But you can do this with every object, that can be created from other values, if you use the ObjectBinding class. 

Here are several examples for that:

Nested or dependant JavaFx Properties

In JavaFx the concept of bindable properties makes life pretty much easier. Here is an example: You want the text of a Label be the same, as in one of your properties: myLabel.textProperty().bind(myProperty);

But sometimes you want to bind to a property of an object, that is held in another property. Lets make an example. You have a property selectedCustomer which holds a Customer object. In that Customer object you have a String property called name. If you bind directly to name with bind(selectedCustomer.get().nameProperty()) you get in trouble, if the value of selectedCustomer changes. Of course you can fix that with implementing a ChangeListener and add it to selectedCustomer and rebind it on the change.

Here is a class, that encapsulated that for you, here is the code for your free use:


This is a Java 8 example and makes use of the new Lamda features. Of course you can use that with replacing the lambdas with anonymous inner classes.

The use is very easy:
ObjectProperty<Customer> selectedCustomer =...;
ObjectProperty<String> selectedName = new NestedObjectProperty<>(selectedCustomer, 
  (Customer customer)-> customer.nameProperty(), false);


The Parameters of the constructor are:

• The property that delivers the property to bind against, in our example selectedCustomer
• A Function implementation, that returns the property to bind against, in our example it gets a Customer as parameter and returns a String property
• A boolean, if the binding should be unidirectional or bidirectional