How to create conditional CellValueFactory for TableView?

Zephyr :

I have a TableView with a column that needs to display one of two values from my data object.

In the MCVE below, I have a Person object that may or may not have a nickname property. This nickname can either be populated, empty, or null.

---

Person.java:

import javafx.beans.property.IntegerProperty;
import javafx.beans.property.SimpleIntegerProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;

public class Person {

    private IntegerProperty id = new SimpleIntegerProperty();
    private StringProperty firstName = new SimpleStringProperty();
    private StringProperty lastName = new SimpleStringProperty();
    private StringProperty nickname = new SimpleStringProperty();

    public Person(int id, String firstName, String lastName, String nickname) {
        this.id.set(id);
        this.firstName.set(firstName);
        this.lastName.set(lastName);
        this.nickname.set(nickname);
    }

    public int getId() {
        return id.get();
    }

    public IntegerProperty idProperty() {
        return id;
    }

    public void setId(int id) {
        this.id.set(id);
    }

    public String getFirstName() {
        return firstName.get();
    }

    public StringProperty firstNameProperty() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName.set(firstName);
    }

    public String getLastName() {
        return lastName.get();
    }

    public StringProperty lastNameProperty() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName.set(lastName);
    }

    public String getNickname() {
        return nickname.get();
    }

    public StringProperty nicknameProperty() {
        return nickname;
    }

    public void setNickname(String nickname) {
        this.nickname.set(nickname);
    }
}

Main.java:

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.control.cell.PropertyValueFactory;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class Main extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) {

        // Simple Interface
        VBox root = new VBox(10);
        root.setAlignment(Pos.CENTER);
        root.setPadding(new Insets(10));

        // Build the simple TableView
        TableView<Person> tableView = new TableView<>();
        TableColumn<Person, String> colId = new TableColumn<>("ID");
        TableColumn<Person, String> colName = new TableColumn<>("Name");

        // Set the cell value factories
        colId.setCellValueFactory(new PropertyValueFactory<>("id"));
        colName.setCellValueFactory(new PropertyValueFactory<>("nickname"));

        // Add the column to the tableview
        tableView.getColumns().addAll(colId, colName);

        // Populate the tableview with a couple of samples
        tableView.getItems().addAll(
                new Person(1, "John", "Williams", null),
                new Person(2, "Marty", "McFly", "Chicken"),
                new Person(3, "Emmett", "Brown", "Doc"),
                new Person(4, "Hans", "Zimmer", "")
        );

        // Add the table to the scene
        root.getChildren().add(tableView);

        // Show the stage
        primaryStage.setScene(new Scene(root));
        primaryStage.setTitle("Sample");
        primaryStage.show();
    }
}

---

What I need is a CellValueFactory that will use the nickname property if it has a value, but the full first and last name of the person if nickname is empty or null.

How do I create a conditional CellValueFactory? I am assuming it requires creating a new Callback function for the factory, but I am not sure how that works.

Slaw :

As @kleopatra hints at, one way to do this is to create a conditional binding in the cellValueFactory. This is done via Bindings.when(ObservableBooleanValue).

nameCol.setCellValueFactory(features -> {
  var firstName = features.getValue().firstNameProperty();
  var lastName  = features.getValue().lastNameProperty();
  var nickname  = features.getValue().nicknameProperty();

  return Bindings.when(nickname.isEmpty())
      .then(firstName.concat(" ").concat(lastName))
      .otherwise(nickname);
});

The isEmpty() binding considers null values to be empty.

Note: If the value of this StringExpression is null, it is considered to be empty.