SimpleStringProperty and SimpleIntegerProperty TableView JavaFX

Question

So i am trying to learn how to use JavaFx Tableview and i stumpled across this tutorial:

Oracle tableview tutorial

in this tutorial they show that in order to fill you tableView you have to fill it with Strings, but not just any String you have to format you String to a SimpleStringProperty

i tried without the format and the result was that none of the information would show!

Also i found that if you want to add an Integer to the table you would have to declare it as an SimpleIntegerProperty

Now i am fairly new to JavaFx but does this mean that when i create an object i have to format all my Integers and Strings to be able to fill my TableView? it seems rather stupid but maybe there is a higher purpose? or is there a way to avoid it?

Answer 1

You don't need to use Properties in your table data objects for them to display, although use of Properties in certain circumstances is desirable.

The following code will display a table of people based on a Person class which has only String fields.

import javafx.application.Application;
import javafx.collections.*;
import javafx.geometry.Insets;
import javafx.scene.*;
import javafx.scene.control.*;
import javafx.scene.control.cell.PropertyValueFactory;
import javafx.scene.layout.VBox;
import javafx.scene.text.Font;
import javafx.stage.Stage;

public class ReadOnlyTableView extends Application {
  private TableView<Person> table = new TableView<Person>();
  private final ObservableList<Person> data =
    FXCollections.observableArrayList(
      new Person("Jacob", "Smith", "[email protected]"),
      new Person("Isabella", "Johnson", "[email protected]"),
      new Person("Ethan", "Williams", "[email protected]"),
      new Person("Emma", "Jones", "[email protected]"),
      new Person("Michael", "Brown", "[email protected]")
    );

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

  @Override public void start(Stage stage) {
    stage.setTitle("Table View Sample");
    stage.setWidth(450);
    stage.setHeight(500);

    final Label label = new Label("Address Book");
    label.setFont(new Font("Arial", 20));

    TableColumn firstNameCol = new TableColumn("First Name");
    firstNameCol.setMinWidth(100);
    firstNameCol.setCellValueFactory(new PropertyValueFactory<Person, String>("firstName"));

    TableColumn lastNameCol = new TableColumn("Last Name");
    lastNameCol.setMinWidth(100);
    lastNameCol.setCellValueFactory(new PropertyValueFactory<Person, String>("lastName"));

    TableColumn emailCol = new TableColumn("Email");
    emailCol.setMinWidth(200);
    emailCol.setCellValueFactory(new PropertyValueFactory<Person, String>("email"));

    table.setItems(data);
    table.getColumns().addAll(firstNameCol, lastNameCol, emailCol);

    final VBox vbox = new VBox();
    vbox.setSpacing(5);
    vbox.setPadding(new Insets(10, 0, 0, 10));
    vbox.getChildren().addAll(label, table);

    stage.setScene(new Scene(new Group(vbox)));
    stage.show();
  }

  public static class Person {
    private String firstName;
    private String lastName;
    private String email;

    private Person(String fName, String lName, String email) {
      this.firstName = fName;
      this.lastName = lName;
      this.email = email;
    }

    public String getFirstName() { return firstName; }
    public void setFirstName(String fName) { firstName = fName; }
    public String getLastName() { return lastName; }
    public void setLastName(String lName) { lastName = lName; }
    public String getEmail() { return email; }
    public void setEmail(String inMail) { email = inMail; }
  }
}

Explanation

The purpose of using Properties and ObservableLists is that these are listenable elements. When properties are used, if the value of a property attribute in the datamodel changes, the view of the item in the TableView is automatically updated to match the updated datamodel value. For example, if the value of a person's email property is set to a new value, that update will be reflected in the TableView because it listens for the property change. If instead, a plain String had been used to represent the email, the TableView would not refresh as it would be unaware of email value changes.

The PropertyValueFactory documentation describes this process in detail:

An example of how to use this class is:

TableColumn<Person,String> firstNameCol = new TableColumn<Person,String>("First Name");
firstNameCol.setCellValueFactory(new PropertyValueFactory<Person,String>("firstName"));  

In this example, the "firstName" string is used as a reference to an assumed firstNameProperty() method in the Person class type (which is the class type of the TableView items list). Additionally, this method must return a Property instance. If a method meeting these requirements is found, then the TableCell is populated with this ObservableValue. In addition, the TableView will automatically add an observer to the returned value, such that any changes fired will be observed by the TableView, resulting in the cell immediately updating.

If no method matching this pattern exists, there is fall-through support for attempting to call get() or is() (that is, getFirstName() or isFirstName() in the example above). If a method matching this pattern exists, the value returned from this method is wrapped in a ReadOnlyObjectWrapper and returned to the TableCell. However, in this situation, this means that the TableCell will not be able to observe the ObservableValue for changes (as is the case in the first approach above).

Update

Here is a contrasting example to the first example which demonstrates how a TableView can observe and automatically refresh based on changes to it's ObservableList of items and changes to the value of a property based item attribute.

import javafx.application.Application;
import javafx.beans.property.*;
import javafx.collections.*;
import javafx.event.*;
import javafx.geometry.Insets;
import javafx.scene.*;
import javafx.scene.control.*;
import javafx.scene.control.cell.PropertyValueFactory;
import javafx.scene.layout.VBox;
import javafx.scene.text.Font;
import javafx.stage.Stage;

public class PropertyBasedTableView extends Application {
  private TableView<Person> table = new TableView<Person>();
  private final ObservableList<Person> data = FXCollections.observableArrayList();
  private void initData() {
    data.setAll(
      new Person("Jacob", "Smith", "[email protected]"),
      new Person("Isabella", "Johnson", "[email protected]"),
      new Person("Ethan", "Williams", "[email protected]"),
      new Person("Emma", "Jones", "[email protected]"),
      new Person("Michael", "Brown", "[email protected]")
    );
  }

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

  @Override public void start(Stage stage) {
    initData();

    stage.setTitle("Table View Sample");
    stage.setWidth(450);
    stage.setHeight(500);

    final Label label = new Label("Address Book");
    label.setFont(new Font("Arial", 20));

    TableColumn firstNameCol = new TableColumn("First Name");
    firstNameCol.setMinWidth(100);
    firstNameCol.setCellValueFactory(new PropertyValueFactory<Person, String>("firstName"));

    TableColumn lastNameCol = new TableColumn("Last Name");
    lastNameCol.setMinWidth(100);
    lastNameCol.setCellValueFactory(new PropertyValueFactory<Person, String>("lastName"));

    TableColumn emailCol = new TableColumn("Email");
    emailCol.setMinWidth(200);
    emailCol.setCellValueFactory(new PropertyValueFactory<Person, String>("email"));

    table.setItems(data);
    table.getColumns().addAll(firstNameCol, lastNameCol, emailCol);
    table.setPrefHeight(300);

    final Button setEmailButton = new Button("Set first email in table to [email protected]");
    setEmailButton.setOnAction(new EventHandler<ActionEvent>() {
      @Override public void handle(ActionEvent event) {
        if (data.size() > 0) {
          data.get(0).setEmail("[email protected]");
        }  
      }
    });

    final Button removeRowButton = new Button("Remove first row from the table");
    removeRowButton.setOnAction(new EventHandler<ActionEvent>() {
      @Override public void handle(ActionEvent event) {
        if (data.size() > 0) {
          data.remove(0);
        }  
      }
    });

    final Button resetButton = new Button("Reset table data");
    resetButton.setOnAction(new EventHandler<ActionEvent>() {
      @Override public void handle(ActionEvent event) {
        initData();
      }
    });

    final VBox vbox = new VBox(10);
    vbox.setPadding(new Insets(10, 0, 0, 10));
    vbox.getChildren().addAll(label, table, setEmailButton, removeRowButton, resetButton);

    stage.setScene(new Scene(new Group(vbox)));
    stage.show();
  }

  public static class Person {
    private final StringProperty firstName;
    private final StringProperty lastName;
    private final StringProperty email;

    private Person(String fName, String lName, String email) {
      this.firstName = new SimpleStringProperty(fName);
      this.lastName = new SimpleStringProperty(lName);
      this.email = new SimpleStringProperty(email);
    }

    public String getFirstName() { return firstName.get(); }
    public void setFirstName(String fName) { firstName.set(fName); }
    public StringProperty firstNameProperty() { return firstName; }
    public String getLastName() { return lastName.get(); }
    public void setLastName(String lName) { lastName.set(lName); }
    public StringProperty lastNameProperty() { return lastName; }
    public String getEmail() { return email.get(); }
    public void setEmail(String inMail) { email.set(inMail); }
    public StringProperty emailProperty() { return email; }  // if this method is commented out then the tableview will not refresh when the email is set.
  }
}