JavaFX Tip 11: Updating Read-Only Properties

Custom controls often feature “read-only” properties. This means that they can not be set from outside the control, not even from their own skin class. It is often the behaviour of a control that leads to a change of the read-only property. In JavaFX this behaviour can be implemented in the control itself and in the skin. So we sometimes end up with a skin wanting to update a read-only property of the control. How can this be done?

Backdoor: Property Map

The solution is quite simple: use the properties map of the control as a backdoor to the control class. The properties map is observable, so if the skin sets a value in the map then the control will be informed and can update the value of the read-only property itself.

The Control Class

The property in the control class might be defined like this:

private final ReadOnlyDoubleWrapper myReadOnly =
   new ReadOnlyDoubleWrapper();

public final ReadOnlyDoubleProperty myReadOnlyProperty() {
    return myReadOnly.getReadOnlyProperty();
}

public final Double ge