CODEWITHSUNDEEP
javamultithreadingjavafx
Shep517
Shep517

Reputation: 25

JavaFX Thread Freezing GUI

I'm still fairly new to threading, and I'm working with javaFX for the first time, so this could be a double whammy! My main issue is with the threading, I believe. I am wanting to crossfade two mediaplayer audios on the skip button. So, I believe that I created a thread to crossfade the audios over two seconds, and then I should end the thread. That's what I "think" I'm doing. However, when the program runs, it usually freezes after the second skip. Most of the code I'm using for javaFX was from tutorials and works as intended before I tried the crossfade. Any advice will be put to great use, TIA! CrossFade class:

import javafx.scene.media.MediaPlayer;
public class CrossFade extends Thread
{
private MediaPlayer mp1;
private MediaPlayer mp2;
private double currentVol;

public CrossFade(MediaPlayer mp1, MediaPlayer mp2)
{
    this.mp1 = mp1;
    this.mp2 = mp2;
    currentVol = mp1.getVolume();
    System.out.println("Vol: " + currentVol);
}

@Override
public void run() {

    mp2.setVolume(0);
    mp2.play();

    //20 increments in volume, every 100ms
    for (int i = 0; i < 20; i ++)
    {
           mp1.setVolume(mp1.getVolume()-currentVol/20);
           mp2.setVolume(mp2.getVolume()+currentVol/20);

           try
           {
               //sleep 100 ms
               Thread.sleep(100);
           }
           catch (InterruptedException e)
           {
               System.out.println("Unable to sleep on xFade");
               e.printStackTrace();
           }
    }
    mp1.stop();
    //this.interrupt();
}

}

Audio class:

import javafx.scene.media.MediaPlayer;
public class Audio{
public static void crossfade(MediaPlayer mp1, MediaPlayer mp2)
{
    Thread xFade = new Thread(new CrossFade(mp1,mp2));
    xFade.start();
}
}

code for the skip button:

skip.setOnAction(new EventHandler<ActionEvent>() {
  @Override public void handle(ActionEvent actionEvent) {
    final MediaPlayer curPlayer = mediaView.getMediaPlayer();
    MediaPlayer nextPlayer = players.get((players.indexOf(curPlayer) + 1) % players.size());
    mediaView.setMediaPlayer(nextPlayer);
    curPlayer.currentTimeProperty().removeListener(progressChangeListener);

    //calls the crossfade in audio class (supposed to start that thread)
    Audio.crossfade(curPlayer,nextPlayer);
    //these were the "old" stop and play calls to the media
    //curPlayer.stop();
    //nextPlayer.play();
  }
});

Upvotes: 0

Views: 1790

Answers (1)

James_D
James_D

Reputation: 209330

In general, you shouldn't change anything that's part of the UI from outside the FX Application Thread. I haven't worked much with MediaPlayers, but I believe they play by the same rules.

You can probably simplify this a lot by using the Animation API. A PauseTransition can be used to manage each pause, and you can "play" these in sequence using a SequentialTransition. This will basically manage all the threading for you. Something like (this is not tested...)

public class Audio{
public static void crossfade(MediaPlayer mp1, MediaPlayer mp2)
{
    double currentVol = mp1.getVolume();
    mp2.setVolume(0);
    mp2.play();
    SequentialTransition crossfade = new SequentialTransition();
    for (int i=0; i<20 i++) {
        PauseTransition pause = new PauseTransition(Duration.millis(100));
        pause.setOnFinished(event -> {
               mp1.setVolume(mp1.getVolume()-currentVol/20);
               mp2.setVolume(mp2.getVolume()+currentVol/20);
        });
        crossfade.getChildren().add(pause);
    }
    crossfade.setOnFinished(event -> mp1.stop());
    crossfade.play();
}
}

Of course, if you're going to use the Animation API, then you may as well use it in a way that does everything "smoothly", instead of in discrete steps:

public class Audio {
public static void crossfade(MediaPlayer mp1, MediaPlayer mp2) {
    final double currentVolume = mp1.getVolume();
    mp2.setVolume(0);
    mp2.play();
    Timeline crossfade = new Timeline(new KeyFrame(Duration.seconds(2), 
            new KeyValue(mp1.volumeProperty(), 0), 
            new KeyValue(mp2.volumeProperty(), currentVolume)));
    crossfade.setOnFinished(event -> mp1.stop());
    crossfade.play();
}
}

Update: If you are still using JavaFX 2.2, replace the lambda expression (crossfade.setOnFinished(event -> mp1.stop());) with an inner class:

crossfade.setOnFinished(new EventHandler<ActionEvent>() {
    @Override
    public void handle(ActionEvent event) {
        mp1.stop();
    }
});

You will also need to declare mp1 as final:

public static void crossfade(final MediaPlayer mp1, final MediaPlayer mp2) { ... }

Upvotes: 2

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