Properties Extractor: Best way to get the ListView instantly updating its elements

Jens DetersNovember 24th, 2014Last Updated: November 23rd, 2014

0 162 3 minutes read

This post is about how to deal with JavaFX ListViews and TableViews and how these controls are getting informed about changed content of the contained elements. I wonder why I didn’t find anything about the following pattern in the relevant books as this is a really crucial mechanism. Many posts out there suggest to force triggering a ChangeEvent getting a ListView to refresh by calling:

list.remove(POJO); list.add(index,POJO);
after each commited change! Brrr!

But there is a much better way:

Enable your list to report changes on the element by providing an properties extractor.

The Demo App

I have created a small demo app to play with for giving it a try. Basically two TableViews and one ListView all sharing the same data. To change properties of the elements one TableView is editable:

The DataModel

The compulsive PersonBean folling the JavaFX Bean Pattern/Convention

public class PersonBean {

    private StringProperty firstName;
    private StringProperty lastName;
    private ObjectProperty<LocalDate> birthday;
    private ObjectBinding<Long> age;

    public PersonBean() {
    }

    public PersonBean(String firstName, String lastName, LocalDate birthday) {
        setFirstName(firstName);
        setLastName(lastName);
        setBirthday(birthday);
    }

    public final StringProperty firstNameProperty() {
        if (firstName == null) {
            firstName = new SimpleStringProperty();
        }
        return firstName;
    }

    public final String getFirstName() {
        return firstNameProperty().get();
    }

    public final void setFirstName(final java.lang.String firstName) {
        firstNameProperty().set(firstName);
    }

    public final StringProperty lastNameProperty() {
        if (lastName == null) {
            lastName = new SimpleStringProperty();
        }
        return lastName;
    }

    public final java.lang.String getLastName() {
        return lastNameProperty().get();
    }

    public final void setLastName(final java.lang.String lastName) {
        lastNameProperty().set(lastName);
    }

    public final ObjectProperty<LocalDate> birthdayProperty() {
        if (birthday == null) {
            birthday = new SimpleObjectProperty<>();
        }
        return birthday;
    }

    public final LocalDate getBirthday() {
        return birthdayProperty().get();
    }

    public final void setBirthday(final java.time.LocalDate birthday) {
        birthdayProperty().set(birthday);

    }

    public String stringValue() {
        return String.format("%s %s %s", getFirstName(), getLastName(), getBirthday().format(DateTimeFormatter.ISO_LOCAL_DATE));
    }

    public final ObjectBinding<Long> ageBinding() {
        if (age == null) {
            age = new ObjectBinding<Long>() {
                {
                    bind(birthdayProperty());
                }

                @Override
                protected Long computeValue() {
                    if (getBirthday() == null) {
                        return null;
                    }
                    return getBirthday().until(LocalDate.now(), ChronoUnit.YEARS);
                }
            };
        }
        return age;
    }

    public static Callback<PersonBean, Observable[]> extractor() {
        return (PersonBean p) -> new Observable[]{p.lastNameProperty(), p.firstNameProperty(), p.birthdayProperty(), p.ageBinding()};
    }
}

DataModel containing a List of randomly created PersonBeans:

public class DataModel {

    private ObservableList<PersonBean> personFXBeans;

    public DataModel() {
        init();
    }

    private void init() {
        personFXBeans = DataSource.getRandomPersonBeansList(100);
    }

    public ObservableList<PersonBean> getPersonFXBeans() {
        return personFXBeans;
    }
}

As you may know to assign a DataModel e.g. to a TableView or a ListView in JavaFX you just have to use the setItems(ObvervableList) method.

@FXML
public void onFillWithDemoDataFXBeans() {
  readOnlyListView.setItems(model.getPersonFXBeans());
  readOnlyTableView.setItems(model.getPersonFXBeans());
  editableTableView.setItems(model.getPersonFXBeans());
}

Now getting a TableView informed about property changes of contained elements is already done you for by the binding either in two ways: via a PropertyValueFactory and by more or less direct property binding:

readOnlyFirstNameColumn.setCellValueFactory(new PropertyValueFactory<>("firstName"));
readOnlyLastNameColumn.setCellValueFactory(new PropertyValueFactory<>("lastName"));
readOnlyBirthdayColumn.setCellValueFactory(new PropertyValueFactory<>("birthday"));
readOnlyAgeColumn.setCellValueFactory(i -> i.getValue().ageBinding());

editableFirstNameColumn.setCellValueFactory(i -> i.getValue().firstNameProperty());
editableLastNameColumn.setCellValueFactory(i -> i.getValue().lastNameProperty());
editableBirthdayColumn.setCellValueFactory(i -> i.getValue().birthdayProperty());
ageColumn.setCellValueFactory(i -> i.getValue().ageBinding());

But the ListView basically only observes the list and not the properties of each element of that list.

When using a ObservableList created by FXCollections.observableArrayList() the ListView will only refresh on ListChange Events like remove() an add() of elements. Therefore:

list.remove(POJO); list.add(index,POJO);
after each commited change.

But there is a much better way:

Enable your list to report changes on the element by providing an properties extractor. You don’t have to care about refreshing then!

ObservableList persons = FXCollections.observableArrayList(PersonBean.extractor());

See DataSource.getRandomPersonBeansList(int length):

public static ObservableList<PersonBean> getRandomPersonBeansList(int length) {
        ObservableList<PersonBean> persons = FXCollections.observableArrayList(PersonBean.extractor());
        for (int i = 0; i < length; i++) {
            persons.add(new PersonBean(getRandomName(), getRandomLastname(), getRandomLocalDate()));
        }
        return persons;
    }

This Extrator is basically a Callback containing an array of Obvervables which are then observed by the Obervablelist (more precicely: ObservableListWrapper):

My PersonBean already provides it’s extrator callback:

public static Callback<PersonBean, Observable[]> extractor() {
   return (PersonBean p) -> new Observable[]{p.lastNameProperty(), p.firstNameProperty(), p.birthdayProperty(), p.ageBinding()};
}

Following this pattern all controls are updated instantly after applying the change.