在javafx.scene.media.MediaPlayer.init使用Media Player時，Java FX空指針異常

Question

在啟動MediaPlayer的Media塊中沒有空字段

我對此進行了廣泛的研究，但沒有發現任何可以解釋此錯誤的信息。

我正在為一個班級項目構建Java Swing應用程序，並嘗試使用JFX面板和媒體播放器來托管和播放多個mp4視頻。 我已經成功地完成了一次工作，但是當我再次回到窗口時，我遇到了錯誤。

com.sun.media.jfxmediaimpl.platform.gstreamer.GSTMediaPlayer.playerSetBalance（Unknown Source）處的com.sun.media.jfxmediaimpl.NativeMediaPlayer.setBalance（javafx.scene.media.MediaPlayer）處的java.lang.NullPointerException。 javafx.scene.media.MediaPlayer上的init（未知源）.project.screens.TutorialPlayerScreen.initMediaPlayer（TutorialPlayerScreen.java:156）處project.screens.TutorialPlayerScreen.init（TutorialPlayerScreen.java:122）處的init（未知源） .projects.buttons.PreKModuleSelectTutorialButtons $ Button $ 7.doAction。 ContentPane.notifiyObserver（ContentPane.java:457）在project.tools.ContentPane $ 1.mousePressed（ContentPane.java:272）在java.awt.Component.processMouseEvent（未知源）在javax.swing.JComponent.processMouseEvent（未知源）在java.awt.Component.pro cessEvent（未知源），位於java.awt.Container.processEvent（未知源），位於java.awt.Container.dispatchEventImpl（未知源），java.awt.Component.dispatchEventImpl（未知源） java.awt.LightweightDispatcher.retargetMouseEvent的來源不明（java.awt.LightweightDispatcher.processMouseEvent的java.awt.LightweightDispatcher.dispatchEvent的來源不明（java.awt.Container.dispatchEventImpl的來源不明） ）處java.awt.Window.dispatchEventImpl（未知源）處java.awt.EventQueue.dispatchEventImpl（未知源）處java.awt.EventQueue.access $ 500（未知源）在java.awt.EventQueue $ 3.run（未知源）在java.awt.EventQueue $ 3.run（未知源）在java.security.AccessController.doPrivileged（本機方法）在java.security.ProtectionDomain $ 1.doIntersectionPrivilege（未知源） ）在java.security.ProtectionDomain $ 1.doIntersectionPrivilege（Un java.awt.EventQueue $ 4.run（未知源）java.awt.EventQueue $ 4.run（未知源）java.security.AccessController.doPrivileged（本機方法）java.security.ProtectionDomain $ 1.doIntersectionPrivilege （未知源）在java.awt.EventQueue.dispatchEvent（未知源）在java.awt.EventDispatchThread.pumpOneEventForFilters（未知源）在java.awt.EventDispatchThread.pumpEventsForFilter（未知源）在java.awt.EventDispatchThread.pumpEventsForHierarchy（未知Source）（java.awt.EventDispatchThread.pumpEvents（未知源）java.awt.EventDispatchThread.pumpEvents（未知源）java.awt.EventDispatchThread.run（未知源）

這是我用來啟動JFX媒體的代碼：

'//媒體播放器支持私有組mediaRoot; 私人場景媒體場景；

private Media tutorialVideo;
private MediaPlayer VideoPlayer;
private MediaView mediaViewer;
private JFXPanel fxPanel;

private int jfxPanelHeight = 394;//525;
private int jfxPanelWidth = 700;//700;

private void initMediaPlayer() throws IOException {
    this.fxPanel = new JFXPanel(); //initializes JFX variables
    fxPanel.setSize(this.jfxPanelWidth ,this.jfxPanelHeight);

    //Add JFX Panel component to the Main Window
    int padding = ((mainWindow.getPreferredSize().width - this.jfxPanelWidth) / 2);
    mainWindow.addLayer(fxPanel, MEDIA_LAYER, padding, 125);

    //Initialize FX Panel
    this.mediaRoot = new Group();
    this.mediaScene = new Scene(this.mediaRoot, 0, 0);

    //Open/prepare the file
    //String tutorialFilePath = new File("").getAbsolutePath() + DIRECTORY_PATH + "Tutorial.mp4";
    String tutorialFilePath = new File("").getAbsolutePath() + MEDIA_PATH + this.observer.getName() +"Tutorial.mp4";
    File mediaFile = new File(tutorialFilePath);
    this.tutorialVideo = new Media(mediaFile.toURI().toString());

    //Create the media player
    this.VideoPlayer = new MediaPlayer(this.tutorialVideo);  //Error here
    this.VideoPlayer.setAutoPlay(false);

    this.mediaViewer = new MediaView(this.VideoPlayer);
    this.mediaViewer.setFitHeight(this.jfxPanelHeight);
    this.mediaViewer.setFitWidth(this.jfxPanelWidth);
          ((Group)this.mediaScene.getRoot()).getChildren().add(this.mediaViewer);

    fxPanel.setScene(this.mediaScene);
}'

我試圖在離開屏幕之前清理使用的內存。

public void tearDown(){

    //Stop the JFX Player and Remove
    this.mainWindow.removeLayer(this.fxPanel);
    this.VideoPlayer.stop();
    this.VideoPlayer.dispose();
    this.fxPanel.removeAll();
    this.mediaRoot.getChildren().removeAll();

    this.mediaRoot = null;
    this.mediaScene = null;
    this.mediaViewer = null;
    this.tutorialVideo  = null;
    this.VideoPlayer = null;
    this.fxPanel = null;
}

private JLayeredPane contentPane;    //The content pane of this JFrame.
public void removeLayer(JComponent component) {
    contentPane.remove(component);
    contentPane.revalidate();
    contentPane.repaint();
}

任何幫助或評論將不勝感激！ 謝謝！

Answer 1

您的代碼中存在線程問題，需要解決。 具體來說，您必須創建FX UI組件並在FX Application線程上設置場景圖。 有關詳細信息，請參見JFXPanel的Javadocs 。

但是，這是空指針異常附帶的。 我認為這是因為當您從UI中完全刪除JFXPanel時，FX工具包正在關閉。 為了防止這種情況，只需致電

Platform.setImplicitExit(false);

首次初始化應用程序時。 （可以從任何線程安全地調用此方法。）

這是外觀類似的SSCCE：

import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.FlowLayout;

import javafx.application.Platform;
import javafx.embed.swing.JFXPanel;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.scene.media.Media;
import javafx.scene.media.MediaPlayer;
import javafx.scene.media.MediaView;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;


public class MediaPlayerInSwing {

    private static final String MEDIA_URL = "http://download.oracle.com/otndocs/products/javafx/oow2010-2.flv" ;

    private JFrame window ;

    private JFXPanel jfxPanel ;
    private Media media ;
    private MediaPlayer player ;
    private MediaView mediaView ;
    private BorderPane root ;
    private Scene scene ;

    private Button button ;

    // create on AWT Event Dispatch Thread
    public MediaPlayerInSwing() {
        Platform.setImplicitExit(false);
        initGUI();
    }

    private void initGUI()  {
        window = new JFrame();
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setLayout(new BorderLayout());

        JPanel controls = new JPanel();
        controls.setLayout(new FlowLayout());
        button = new Button("Show video");
        controls.add(button);
        button.addActionListener(e -> {
            if (jfxPanel == null) {
                showVideo();
            } else {
                tearDownVideo();
            }
        });

        window.add(controls, BorderLayout.SOUTH);
        window.setSize(600, 480);
        window.setLocationRelativeTo(null);
        window.setVisible(true);
    }

    private void showVideo() {


        jfxPanel = new JFXPanel();

        Platform.runLater(() -> {
            media = new Media(MEDIA_URL);
            player = new MediaPlayer(media);
            player.play(); 
            mediaView = new MediaView(player);
            root = new BorderPane(mediaView);
            scene = new Scene(root, 600, 400);
            jfxPanel.setScene(scene);
        });

        window.add(jfxPanel, BorderLayout.CENTER);
        button.setLabel("Hide video");
    }

    private void tearDownVideo() {

        window.remove(jfxPanel);

        Platform.runLater(() -> {
            player.stop();
            player.dispose();
            player = null ;
            mediaView = null ;
            root = null ;
            jfxPanel.setScene(null);
            scene = null ;
            SwingUtilities.invokeLater(() -> {
                jfxPanel = null ;
                // force window to repaint...
                window.getRootPane().repaint();
            });
        });
        button.setLabel("Show video");
    }

    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeLater(MediaPlayerInSwing::new);
    }
}

Answer 2

這可能不是導致NullPointerException的問題，但是您需要在不同的線程上進行不同的方法調用。 特別是，必須在AWT事件分配線程上調用new JFXPanel（），而其他initMediaPlayer則需要在FX Application線程上調用。 請參閱JFXPanel javadocs。 （雖然這可能不是問題的原因，但可以想象是這樣的。）– James_D

這樣就解決了問題。

我將JFX Panel設置為由主窗口管理，並且永遠不會超出范圍。 為了僅在我想要的屏幕上解決可見性問題，我將功能更改為這些...

public void tearDown(){
    this.mediaPanel.getMediaPanel().setVisible(false);
    this.VideoPlayer.stop();
}

和

private void initMediaPlayer() throws IOException {
    this.mediaPanel.getMediaPanel().setVisible(true);

    //Initialize FX Panel
    this.mediaRoot = new Group();
    this.mediaScene = new Scene(this.mediaRoot, 0, 0);

    //Open/prepare the file
    //String tutorialFilePath = new File("").getAbsolutePath() + DIRECTORY_PATH + "Tutorial.mp4";
    String tutorialFilePath = new File("").getAbsolutePath() + MEDIA_PATH + this.observer.getName() +"Tutorial.mp4";
    File mediaFile = new File(tutorialFilePath);
    this.tutorialVideo = new Media(mediaFile.toURI().toString());

    //Create the media player
    this.VideoPlayer = new MediaPlayer(this.tutorialVideo);  //Error here
    this.VideoPlayer.setAutoPlay(false);

    this.mediaViewer = new MediaView(this.VideoPlayer);
    this.mediaViewer.setFitHeight(this.mediaPanel.getPanelHeight());
    this.mediaViewer.setFitWidth(this.mediaPanel.getPanelWidth());
        ((Group)this.mediaScene.getRoot()).getChildren().add(this.mediaViewer);

    this.mediaPanel.getMediaPanel().setScene(this.mediaScene);
}

感謝所有提供幫助的人！