How to create custom binding types in JavaFX

I have a custom class named timeelapsed (it is immutable) Timeelapsed has a constructor that accepts a duration (which is the type used to track time in JavaFX mediaplayer) The constructor then converts the duration to timeelapsed

The problem is that I have a function that needs to return timeelapsed observablevalue What I need is to be able to do such things:

new Binding<TimeElapsed>() {

     {
          super.bind(player.duration())
     }

     @Override
     protected TimeElapsed computeValue() {
          return new TimeElapsed(player.duration());
     }
}

But for some reason, without binding generics, you can only use doublebinding and similar things. You calculate values there, but you can't select types So what should I do?

Solution

Use the sample solution of objectbinding < timeelapsed >

Key methods

/* @return an ObjectBinding of immutable TimeElapsed objects for the player */
private ObjectBinding<TimeElapsed> createElapsedBindingByBindingsAPI(
        final MediaPlayer player
    ) {
    return Bindings.createObjectBinding(
        new Callable<TimeElapsed>() {
            @Override
            public TimeElapsed call() throws Exception {
                return new TimeElapsed(player.getCurrentTime());
            }
        },player.currentTimeproperty()
    );
}

Complete executable example

Change media in the sample_ Path to match the media you need

import javafx.application.Application;
import javafx.beans.binding.*;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.layout.StackPane;
import javafx.scene.media.*;
import javafx.stage.Stage;
import javafx.util.Duration;

import java.io.File;
import java.net.MalformedURLException;
import java.util.concurrent.Callable;

/** Displays progress (time elapsed in seconds) of playing a media file. */    
public class TimeElapsedBinding extends Application {
    private static final String MEDIA_PATH = 
        "C:\\Users\\Public\\Music\\Sample Music\\Dillon - Thirteen Thirtyfive.mp3";

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

    @Override public void start(Stage stage) throws Exception {
        final MediaView   mediaView    = createMediaView();
        final MediaPlayer player       = mediaView.getMediaPlayer();
        final Label       elapsedLabel = new Label();

        ObjectBinding<TimeElapsed> elapsedBinding =
            createElapsedBindingByBindingsAPI(player);
        StringBinding elapsedStringBinding =
            createStringBindingByBindingsAPI(elapsedBinding);

        elapsedLabel.textproperty().bind(
                elapsedStringBinding
        );

        StackPane layout = new StackPane();
        layout.setStyle("-fx-background-color: cornsilk; -fx-padding: 20px;");
        layout.getChildren().setAll(
                mediaView,elapsedLabel
        );

        stage.setScene(new Scene(layout));
        stage.show();
    }

    /* @return an ObjectBinding of immutable TimeElapsed objects for the player */
    private ObjectBinding<TimeElapsed> createElapsedBindingByBindingsAPI(
            final MediaPlayer player
        ) {
        return Bindings.createObjectBinding(
            new Callable<TimeElapsed>() {
                @Override
                public TimeElapsed call() throws Exception {
                    return new TimeElapsed(player.getCurrentTime());
                }
            },player.currentTimeproperty()
        );
    }

    /* @return a string binding to an ObjectBinding of immutable TimeElapsed objects */
    private StringBinding createStringBindingByBindingsAPI(
            final ObjectBinding<TimeElapsed> elapsedBinding
        ) {
        return Bindings.createStringBinding(
                new Callable<String>() {
                    @Override
                    public String call() throws Exception {
                        return String.format(
                                "%.0f",elapsedBinding.getValue().getElapsed()
                        );
                    }
                },elapsedBinding
        );
    }

    /* @Return a new MediaView from a predefined MEDIA_PATH string */
    private MediaView createMediaView() throws MalformedURLException {
        String mediaURI = new File(MEDIA_PATH).toURI().toURL().toExternalForm();

        Media media = new Media(mediaURI);
        MediaPlayer player = new MediaPlayer(media);
        MediaView mediaView = new MediaView(player);
        player.play();

        return mediaView;
    }

    /** immutable TimeElapsed class. */
    class TimeElapsed {
        private final double elapsed;

        TimeElapsed(Duration duration) {
            elapsed = duration.toSeconds();
        }

        public double getElapsed() {
            return elapsed;
        }
    }
}

The above is only provided as a sample to adapt to the problem framework of using immutable objects in objectbinding, not the most effective way to track the progress of playing media

Alternative implementation

If I do not need to use immutable objects in objectbinding, I will directly monitor the progress attribute of mediaplayer, similar to the following code:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ProgressBar;
import javafx.scene.layout.StackPane;
import javafx.scene.media.*;
import javafx.stage.Stage;

import java.io.File;
import java.net.MalformedURLException;

public class MediaProgressMonitoring extends Application {
    private static final String MEDIA_PATH = "C:\\Users\\Public\\Music\\Sample Music\\Dillon - Thirteen Thirtyfive.mp3";

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

    @Override public void start(Stage stage) throws Exception {
        final MediaView   mediaView = createMediaView();
        final MediaPlayer player    = mediaView.getMediaPlayer();
        final ProgressBar progress  = new ProgressBar(0);
        progress.setPrefWidth(800);

        player.currentTimeproperty().addListener((observable) ->
            progress.setProgress(
                player.getCurrentTime().toMillis() / 
                player.getTotalDuration().toMillis()
            )
        );

        StackPane layout = new StackPane();
        layout.setStyle("-fx-background-color: cornsilk; -fx-padding: 20px;");
        layout.getChildren().setAll(
                mediaView,progress
        );

        stage.setScene(new Scene(layout));
        stage.show();
    }

    private MediaView createMediaView() throws MalformedURLException {
        String mediaURI = new File(MEDIA_PATH).toURI().toURL().toExternalForm();

        Media media = new Media(mediaURI);
        MediaPlayer player = new MediaPlayer(media);
        MediaView mediaView = new MediaView(player);
        player.play();

        return mediaView;
    }
}