JavaFX How to set String values to TableView

Question

To give some background: I now am able to load files onto my mp3 program and play them but all the values in my tableview are null?

My song class

package application;

//imports here

public class Song {
private String title;
private String artist;
private String album;
private SimpleStringProperty pTitle;
private SimpleStringProperty pArtist;
private SimpleStringProperty pAlbum;
private Media music;
private MediaPlayer mp;
private Image coverArt;

public Song(File file) {
    music = new Media(file.toURI().toString());
    music.getMetadata().addListener((Change<? extends String, ? extends Object> c) -> {
        if (c.wasAdded()) {
            if ("artist".equals(c.getKey())) {
                System.out.println(c.getKey()+":"+c.getValueAdded());
                this.pArtist = new SimpleStringProperty(c.getValueAdded().toString());
                //pArtist.set(c.getValueAdded().toString());
                artist = c.getValueAdded().toString();  
            } else if ("title".equals(c.getKey())) {
                title = c.getValueAdded().toString();
                System.out.println(c.getKey()+":"+c.getValueAdded());
            } else if ("album".equals(c.getKey())) {
                album = c.getValueAdded().toString();
                System.out.println(c.getKey()+":"+c.getValueAdded());
            } else if ("image".equals(c.getKey())) {
                coverArt = (Image) c.getValueAdded();
            }
        }
    });
    mp = new MediaPlayer(music);
    System.out.println(pArtist);
    System.out.println(artist);
    //artist = (String) mp.getMedia().getMetadata().get("artist");
    //title = (String) music.getMetadata().get("title");
    //album = (String) music.getMetadata().get("album");
    //artist = "test";
    //album = "test";
    //title = "test";
}

public void play() {
    mp.play();
}

public void pause() {
    mp.pause();
}

public void stop() {
    mp.stop();
}

public String getTitle(){
    return title;
}

public void setTitle(String title){
    this.title = title;
}

public String getArtist(){
    return artist;
}

public void setArtist(String artist){
    this.artist = artist;
}

public String getAlbum(){
    return album;
}

public void setAlbum(String album){
    this.album = album;
}

public Image getCover(){
    return coverArt;
}

public MediaPlayer getMP(){
    return mp;
}





}

Weirdly enough at first I thought it was because my String variables were not setting correctly and were set to null since it shows as null in the console when I put these print lines to test it when the Song object is being constructed. Here is a sample of the console when I test this.

null
null
artist:Foo Fighters
album:Saint Cecilia EP
title:Saint Cecilia

Here is my controller class

public class SceneController implements Initializable{
@FXML
private Button stopBtn;
@FXML
private Slider volume;
@FXML
private Button loadBtn;
@FXML
private Button playBtn;
@FXML
private TableView<Song> table;
@FXML
private Label label;
@FXML
private ProgressBar proBar;
private TableColumn songCol,artistCol,albumCol;
ObservableList<Song> songList = FXCollections.observableArrayList();
List<File> list;
FileChooser fileChooser = new FileChooser();
Desktop desktop;
Song mySong;



@Override
public void initialize(URL arg0, ResourceBundle arg1) {
    TableColumn songCol = new TableColumn("Song");
    TableColumn artistCol = new TableColumn("Artist");
    TableColumn albumCol = new TableColumn("Album");

    songCol.setCellValueFactory(
            new PropertyValueFactory<Song,String>("title"));
    //songCol.setCellFactory(new Callback);
    artistCol.setCellValueFactory(
            new PropertyValueFactory<Song,String>("artist"));
    albumCol.setCellValueFactory(
            new PropertyValueFactory<Song,String>("album"));
    volume.setMin(0);
    volume.setMax(100);
    volume.setValue(100);
    volume.valueProperty().addListener(new InvalidationListener() {
        @Override
        public void invalidated(Observable observable) {
            mySong.getMP().setVolume(volume.getValue()/100.0);
        }

    });

}

// Event Listener on Button[#loadBtn].onAction
@FXML
public void loadFile(ActionEvent event) {
    Node source = (Node) event.getSource();
    Window theStage = source.getScene().getWindow();
    //set fileChooser filter
    FileChooser.ExtensionFilter extFilter = new FileChooser.ExtensionFilter("MP3 files", "*.mp3");
    fileChooser.getExtensionFilters().add(extFilter);
    fileChooser.setTitle("Select MP3 files");
    //File file = fileChooser.showOpenDialog(theStage);
    //mySong = new Song(file);
    list = fileChooser.showOpenMultipleDialog(theStage);
    if(list!=null){
        for(File x: list) {
            mySong = new Song(x);
            System.out.println(mySong.getTitle());
            songList.add(mySong);
        }
    }
    table.setItems(songList);
}

@FXML
public void playSong(ActionEvent event) {
    mySong.play();
}

@FXML
public void stopSong(ActionEvent event) {
    //mySong.pause();
    System.out.println("song title: "+mySong.getArtist()+mySong.getTitle());
    ImageView img = new ImageView(mySong.getCover());
    //img.fitWidthProperty().bind(label.widthProperty());
    //img.fitHeightProperty().bind(label.heightProperty());
    img.setFitHeight(120);
    img.setFitWidth(200);
    label.setGraphic(img);
    //label.setGraphic(new ImageView(mySong.getCover()));
}

But I made another test print line for my "Stop" button in the controller class and after everything is loaded and I press it, it prints out the artist and title fine. I have saw this other thread and checked my getter methods and they seem to be correct? I am really lost on this and if anyone could provide some insight and a solution as to whether it is because my variables are null or my PropertyValueFactory is not done correctly

Also I notice that the nulls come first even though should they not be the last thing printed since when I create a new song object in my controller class the first print lines that run are in the if statements?

Answer 1

There are several things wrong with the way you have your current code, that are evident from the limited example you posted in the question:

1. Your Song class does not properly follow the JavaFX properties pattern. In particular, you store each "property" twice, once in a "traditional" JavaBean-style field, for example private String title, and once in a JavaFX property: private StringProperty pTitle;. Each property should be stored once. If you want the table to be aware when the value changes, you should use JavaFX properties, and have the "standard" getXXX() and setXXX() retrieve and set the underlying values stored in those properties.
2. The listener you attach to the media's metadata is called asynchronously at some indeterminate point in the future. When you add the song to the table's list, the cell value factories attached to the columns will, at some point, be executed, and retrieve the assigned property from the Song instance. With the code the way you currently have it, those property instances are only actually created once the listener on the metadata is invoked. So it is possible (perhaps likely) that the cell value factory will inspect the Song instance for its property before the JavaFX property is instantiated, making it impossible for the table to properly observe the property and respond to changes in it. You should instantiate the JavaFX properties when the Song instance is created, and set their value in the listener on the metadata.
3. At no point do you add the columns you create in the controller to the table. If you are creating them in the FXML file (which you didn't post in the question), you should inject those columns into the controller and initialize those columns with the cell value factories. (Since the screenshot shows there are columns in the table, I am going to assume they are defined in the FXML file, and have appropriate fx:ids.)

So your Song class should look something like this:

public class Song {

    private final StringProperty title = new SimpleStringProperty();
    private final StringProperty artist = new SimpleStringProperty();
    private final StringProperty album = new SimpleStringProperty();
    private Media music;
    private MediaPlayer mp;
    private Image coverArt;

    public Song(File file) {
        music = new Media(file.toURI().toString());
        music.getMetadata().addListener((Change<? extends String, ? extends Object> c) -> {
            if (c.wasAdded()) {
                if ("artist".equals(c.getKey())) {
                    setArtist(c.getValueAdded().toString());
                } else if ("title".equals(c.getKey())) {
                    setTitle(c.getValueAdded().toString());
                } else if ("album".equals(c.getKey())) {
                    setAlbum(c.getValueAdded().toString());
                } else if ("image".equals(c.getKey())) {
                    // maybe this needs to be a JavaFX property too: it is not clear from your question:
                    coverArt = (Image) c.getValueAdded();
                }
            }
        });
        mp = new MediaPlayer(music);
    }

    public void play() {
        mp.play();
    }

    public void pause() {
        mp.pause();
    }

    public void stop() {
        mp.stop();
    }

    public StringProperty titleProperty() {
        return title ;
    }

    public final String getTitle(){
        return titleProperty().get();
    }

    public final void setTitle(String title){
        titleProperty().set(title);
    }

    public StringProperty artistProperty() {
        return artist ;
    }

    public final String getArtist(){
        return artistProperty().get();
    }

    public final void setArtist(String artist){
        artistProperty.set(artist);
    }

    public StringProperty albumProperty() {
        return album ;
    }

    public final String getAlbum(){
        return albumProperty().get();
    }

    public final void setAlbum(String album){
        albumProperty().set(album);
    }

    public Image getCover(){
        return coverArt;
    }

    public MediaPlayer getMP(){
        return mp;
    }


}

For your controller, I am going to assume your FXML file has defined table columns with fx:ids of "songCol", "artistCol", and "albumCol", respectively. You need to inject these into the controller as you do with the other columns. I also strongly recommend not using the PropertyValueFactory class, which uses reflection and lacks much in the way of compile-time checking, and implementing the callback yourself. Using lambda expressions makes this pretty easy.

So your controller should look like:

public class SceneController implements Initializable{

    // non-table code omitted...

    @FXML
    private TableView<Song> table;
    @FXML
    private Label label;
    @FXML
    private ProgressBar proBar;
    @FXML
    private TableColumn<Song, String> songCol ;
    @FXML
    private TableColumn<Song, String> artistCol ;
    @FXML
    private TableColumn<Song, String> albumCol;

    ObservableList<Song> songList = FXCollections.observableArrayList();
    List<File> list;
    FileChooser fileChooser = new FileChooser();
    Desktop desktop;
    Song mySong;

    @Override
    public void initialize(URL arg0, ResourceBundle arg1) {

        songCol.setCellValueFactory(cellData -> cellData.getValue().titleProperty());
        artistCol.setCellValueFactory(cellData -> cellData.getValue().artistProperty());
        albumCol.setCellValueFactory(cellData -> cellData.getValue().albumProperty());

        // ...

    }

    // other non-table code omitted...

}

You didn't post an minimal, complete, verifiable example, so there may well be other errors in your code which prevent the table from displaying correctly. This should get you started, however.

Answer 2

Normally the TableColumns would be defined in FXML and injected via @FXML.

• See the Oracle TableView FXML example.

If you don't want to do it that way, you need to do:

table.getColumns().add(songCol);

And similarly for your other columns.

Also, as HypnicJerk pointed out in comments you also need to follow appropriate naming conventions when using the PropertyValueFactory.

songCol.setCellValueFactory(
    new PropertyValueFactory<Song,String>("title")
);

For more details see:

• Javafx tableview not showing data in all columns