播放器播放视频但未在屏幕上显示

Question

当我尝试播放任何视频时，我可以听到音频，但屏幕上没有视频。我尝试以相同的方式添加菜单，但是有效但播放器类没有正确添加到舞台上。

//这里所有的进口...... !!!

    public class MyPlayerLauncher extends Application
{

    static Stage stage1;
    static Player player;
    static ViewManager viewmanager;

    public static void main(String a[])
    {
        launch(a);
    }
    public void start(Stage stage)
    {
        ViewManager viewmanager = new ViewManager();
        Scene scene = new Scene(viewmanager, 1000, 600, Color.BLACK);
        stage.setScene(scene);
        stage.show();       
    }
}


public class ViewManager extends BorderPane
{
    Button play, stop, forward, backward, next, previous, loop;
    Slider volume, seekbar;
    Label volume_label, start_time, end_time;
    Pane bpane = new Pane();
    Player player;

    MenuManager menumanager = new MenuManager();

    public ViewManager()
    {
        this.menumanager.menus();
        this.setTop(menumanager.menus());



        setPadding(new Insets(5,10,5,10));
        play = new Button("|>");
        play.setPrefWidth(70);
        play.setPrefHeight(70);
        play.setMinHeight(30);
        play.setMinWidth(30);

        stop = new Button("[]");
        stop.setPrefWidth(70);
        stop.setPrefHeight(70);
        stop.setMinHeight(30);
        stop.setMinWidth(30);

        forward = new Button(">>");
        forward.setPrefWidth(70);
        forward.setPrefHeight(70);
        forward.setMinHeight(30);
        forward.setMinWidth(30);

        backward = new Button("<<");
        backward.setPrefWidth(70);
        backward.setPrefHeight(70);
        backward.setMinHeight(30);
        backward.setMinWidth(30);

        next = new Button(">>|");
        next.setPrefWidth(70);
        next.setPrefHeight(70);
        next.setMinHeight(30);
        next.setMinWidth(30);

        previous = new Button("|<<");
        previous.setPrefWidth(70);
        previous.setPrefHeight(70);
        previous.setMinHeight(30);
        previous.setMinWidth(30);

        loop = new Button("@");
        loop.setPrefWidth(70);
        loop.setPrefHeight(70);
        loop.setMinHeight(30);
        loop.setMinWidth(30);


        volume = new Slider();
        volume.setPrefWidth(500);

        bpane.setStyle("-fx-background-color:#bfc2c7");
        bpane.getChildren().addAll(play, stop, backward, forward, previous, next, loop);
        this.setBottom(bpane);

    }
    public void play(File file)
    {
        String received_file = null;
        try
        {
            received_file = file.toURI().toURL().toExternalForm();
            System.out.println(received_file);
            player = new Player(received_file);
            setCenter(player);
        }
        catch (MalformedURLException e)
        {
            e.printStackTrace();
        }
    }

}


public class Player extends BorderPane
{
    Media media;
    MediaPlayer mediaplayer;
    MediaView mediaview;
    Pane mpane;
    MenuManager mm = new MenuManager();

    public Player(String file)
    {
        String playable_file = file;

        media = new Media(playable_file);
        mediaplayer = new MediaPlayer(media);
        mediaview = new MediaView(mediaplayer);

        mpane = new Pane();
        mpane.getChildren().add(mediaview);

        setCenter(mpane);

        mediaplayer.play();



    }
}


public class MenuManager
{
    Player layer;
    FileChooser filechooser;
    ViewManager viewmanager;
    Stage stage;
    MyPlayerLauncher mm;

    public Node menus()
    {
        MenuBar menubar = new MenuBar();
        Menu file = new Menu("_File");
        MenuItem open = new MenuItem("_Open");
        MenuItem openmultiple = new MenuItem("_Open Multiple files");
        MenuItem openfolder = new MenuItem("_Open Folder");
        MenuItem quit = new MenuItem("_Quit");

        file.getItems().add(open);
        file.getItems().add(openmultiple);
        file.getItems().add(openfolder);
        file.getItems().add(quit);
        menubar.getMenus().add(file);

        open.setOnAction(new EventHandler<ActionEvent>()
        {
            public void handle(ActionEvent e)
            {
                stage = mm.stage1;
                filechooser = new FileChooser();
                File file = filechooser.showOpenDialog(stage);
                if(file != null)
                {
                    viewmanager = new ViewManager();
                    viewmanager.play(file);
                }
                else
                {
                    System.exit(0);
                }
            }   
        });
        quit.setOnAction(new EventHandler<ActionEvent>()
                {
                    public void handle(ActionEvent e)
                    {
                        System.exit(0);
                    }   
                });

        return menubar;
    }
}