Using the Media Classes - JavaFX 8: A Definitive Guide to Building Desktop, Mobile, and Embedded Java Clients - page 402

lambda expression is called on the JavaFX application thread. Inside the run body of the lambda expression we
get the currentTime from the MediaPlayer and pass it as a parameter to the updatePositionSlider method. The
updatePositionSlider method, also shown in Listing 9-19, first checks to see if the positionSlider 's value is
currently changing and, if so, returns without doing anything. We do this to make sure we don't change the slider's
position while the user is currently dragging it. Doing so would make the slider's thumb bar flicker back and forth
between the drag position and the position indicated by the currentTime value. Needless to say, this is an unwanted
effect that we are careful to avoid. If the user is not currently changing the position slider's value, we are free to update
it based on the value of currentTime and totalDuration . The position slider is created with minimum and maximum
values of 0.0 and 1.0. The currentTime value is therefore divided by the media's totalDuration to calculate the
correct value for the slider. If either totalDuration or currentValue is null, the slider is simply positioned at 0.
You probably noticed that the CurrentTimeListener also formats the value of currentTime and displays it as
the text of the currentTimeLabel . If you refer back to Figure 9-5 you can see that the position slider is bracketed by
two Label controls. On the left is a label that displays the currentTime value, and the totalDuration is displayed
by a label to the right of the slider. The label displaying the totalDuration is set by a listener that is attached to
MediaPlayer 's totalDuration property much like the CurrentTimeListener shown earlier. Whenever the value of
totalDuration changes, the listener calls the formatDuration method to create a String to use as the label's text. The
formatDuration method used to format both of these values is shown in Listing 9-20.
Listing 9-20. The formatDuration Method
private String formatDuration(Duration duration) {
double millis = duration.toMillis();
int seconds = (int) (millis / 1000) % 60;
int minutes = (int) (millis / (1000 * 60));
return String.format("%02d:%02d", minutes, seconds);
}
The formatDuration method takes a Duration as a parameter and returns a String with the format mm : ss where
mm is minutes and ss is seconds. The minutes and seconds values will be zero-padded if they are only one digit long.
The second part of the position slider's job is to allow the user to set the playback position by dragging the slider
back and forth. This is accomplished by listening for changes to the Slider 's valueChangingProperty as shown in
Listing 9-21.
Listing 9-21. Listening to Position Slider Changes and Seeking
@Override
protected Node initView() {
// Controls are created as shown in Listing 9-15.
positionSlider = createSlider("positionSlider");
positionSlider.valueChangingProperty().addListener(new PositionListener());
// Lay out the GridPane as shown in Listing 9-15.
}
private class PositionListener implements ChangeListener<Boolean> {
@Override
public void changed(ObservableValue<? extends Boolean> observable,
Boolean oldValue, Boolean newValue) {
if (oldValue && !newValue) {
double pos = positionSlider.getValue();
final MediaPlayer mediaPlayer = songModel.getMediaPlayer();