FXObservableWithList.java

import java.util.ArrayList;
import java.util.List;

import javafx.beans.property.ListProperty;
import javafx.beans.property.Property;
import javafx.beans.property.SimpleListProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.beans.value.WritableObjectValue;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;

public class FXObservableWithList
{
    private Object theList;

    public List<String> getTheList()
    {
        if (theList == null)
        {
            theList = new ArrayList<String>();
        }
        if (theList instanceof WritableObjectValue)
        {
            return ((WritableObjectValue<ObservableList<String>>)theList).get();
        }
        return (List<String>)theList;
    }

    public void setTheList(List<String> theList)
    {
        if (this.theList instanceof Property)
        {
            ((Property<ObservableList<String>>)this.theList).setValue(toObservableList(theList));
        }
        else
        {
            this.theList = theList;
        }
    }

    public ObservableList<String> theListObservables()
    {
        if (this.theList instanceof Property)
        {
            return ((Property<ObservableList<String>>)this.theList).getValue();
        }
        theList = toObservableList((List<String>)theList);
        return (ObservableList<String>)theList;
    }

    public Property<ObservableList<String>> theListProperty()
    {
        if (!(theList instanceof WritableObjectValue))
        {
            theList = new SimpleObjectProperty<List<String>>(this, "theList", theListObservables());
        }
        return (Property<ObservableList<String>>)theList;
    }

    public ListProperty<String> theListListProperty()
    {
        if (!(theList instanceof ListProperty))
        {
            Property<ObservableList<String>> oldProperty = null;
            if (theList instanceof Property)
            {
                oldProperty = (Property<ObservableList<String>>)theList;
            }
            theList = new SimpleListProperty<String>(this, "theList", theListObservables());
            if (oldProperty != null)
            {
                oldProperty.bind((ListProperty<String>)theList);
            }
        }
        return (ListProperty<String>)theList;
    }

    private ObservableList<String> toObservableList(List<String> list)
    {
        if (list instanceof ObservableList)
        {
            return (ObservableList<String>)list;
        }
        if (list != null)
        {
            return FXCollections.observableList(list);
        }
        return FXCollections.observableArrayList();
    }
}

FXObservableWithListSpec.groovy

import javafx.beans.property.*
import javafx.collections.*
import spock.lang.Specification

class FXObservableWithListSpec extends Specification {

    FXObservableWithList observable = new FXObservableWithList()

    def "list is never null"() {
        expect:
        observable.getTheList() == []
        !(observable.getTheList() instanceof ObservableList)
    }

    def "can add and remove a list"() {
        when:
        observable.setTheList(['foo'])

        then:
        observable.getTheList() == ['foo']
    }

    def "can get the observable list"() {
        expect:
        observable.theListObservables() == []
        (observable.theListObservables() instanceof ObservableList)
        (observable.getTheList() instanceof ObservableList)
    }

    def "can get the Property"() {
        expect:
        observable.theListProperty() instanceof ObjectProperty
        observable.getTheList() == []
    }

    def "can get the ListProperty"() {
        expect:
        observable.theListListProperty() instanceof ListProperty
        observable.theListProperty() instanceof ListProperty
    }

    def "when bound to the property changing to listProperty notifies the listener"() {
        given:
        Property<ObservableList<String>> property = observable.theListProperty()
        ListProperty listProperty = new SimpleListProperty<String>()

        expect:
        listProperty.get() == null

        when:
        listProperty.bind(property)

        then:
        listProperty.get() == []

        when:
        observable.setTheList(['foo'])

        then:
        listProperty.get() == ['foo']

        when:
        observable.theListListProperty()
        observable.setTheList(['bar'])

        then:
        listProperty.get() == ['bar']
    }
}