Nachdem ich das gelernt habedispose() sollte angerufen werdenGraphics/Graphics2D Ich habe mein Spiel geändert, um dies zu berücksichtigen.

Als ich hinzufügteg2d.dispose() in überschriebenpaintComponent(Graphics g) vonJPanel, meine Komponenten, die ich hinzugefügt habe (Erweiterungen vonJLabel klasse) wo nicht gerendert konnte ich sie noch anklicken etc aber sie wären es nichtgemalt.

Ich habe mit einem normalen getestetJLabel undJButton mit dem gleichen effekt (obwohlJButton wird gerendert, wenn sich die Maus darüber befindet).

Meine Frage ist also, warum das passiert?

Hier ist eine SSCCE, um zu demonstrieren:

nach unkommentiertem anruf andispose() impaintComponent vonMainMenuPanel Klasse:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Image;
import java.awt.RenderingHints;
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
import java.net.URL;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Test {

    public Test() {
        try {
            initComponents();
        } catch (Exception ex) {
            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Test();
            }
        });
    }

    private void initComponents() throws Exception {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);

        MainMenuPanel mmp = new MainMenuPanel();
        frame.add(mmp);

        frame.pack();
        frame.setVisible(true);
    }
}

class MainMenuPanel extends JPanel {

    //create labels for Main Menu
    private PopUpJLabel versusesModeLabel;
    private PopUpJLabel singlePlayerModeLabel;
    private PopUpJLabel optionsLabel;
    private PopUpJLabel helpLabel;
    private PopUpJLabel aboutLabel;
    //create variable to hold background
    private Image background;
    private Dimension preferredDimensions;
    public static String gameType;
    public static final String SINGLE_PLAYER = "Single Player", VERSUS_MODE = "VS Mode";

    /**
     * Default constructor to initialize double buffered JPanel with
     * GridBagLayout
     */
    public MainMenuPanel() {
        super(new GridBagLayout(), true);
        try {
            initComponents();
        } catch (Exception ex) {
            JOptionPane.showMessageDialog(null, "Could not load main menu background!", "Main Menu Error: 0x004", JOptionPane.ERROR_MESSAGE);
            System.exit(4);
        }
    }

    /*
     * Create JPanel and its components
     */
    private void initComponents() throws Exception {

        //set prefered size of JPanel
        preferredDimensions = new Dimension(800, 600);

        background = scaleImage(800, 600, ImageIO.read(new URL("http://photos.appleinsider.com/12.08.30-Java.jpg")));

        //create label instances
        singlePlayerModeLabel = new PopUpJLabel("Single Player Mode");
        singlePlayerModeLabel.setEnabled(false);

        versusesModeLabel = new PopUpJLabel("Versus Mode");
        optionsLabel = new PopUpJLabel("Options");
        helpLabel = new PopUpJLabel("Help");
        aboutLabel = new PopUpJLabel("About");

        //create new constraints for gridbag
        GridBagConstraints gc = new GridBagConstraints();
        gc.fill = GridBagConstraints.HORIZONTAL;
        gc.ipady = 50;//vertical spacing 

        //add newGameLabel to panel with constraints
        gc.gridx = 0;
        gc.gridy = 0;
        add(singlePlayerModeLabel, gc);

        gc.gridy = 1;
        add(versusesModeLabel, gc);
        //add optionsLabel to panel with constraints (x is the same)
        gc.gridy = 2;
        add(optionsLabel, gc);
        //add helpLabel to panel with constraints (x is the same)
        gc.gridy = 3;
        add(helpLabel, gc);
        //add aboutLabel to panel with constraints (x is the same)
        gc.gridy = 4;
        add(aboutLabel, gc);
    }

    public static BufferedImage scaleImage(int w, int h, BufferedImage img) throws Exception {
        BufferedImage bi;
        //bi = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
        bi = new BufferedImage(w, h, img.getType());
        Graphics2D g2d = (Graphics2D) bi.createGraphics();
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2d.addRenderingHints(new RenderingHints(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY));
        g2d.drawImage(img, 0, 0, w, h, null);
        g2d.dispose();
        return bi;
    }

    /*
     * Will return the preffered size of JPanel
     */
    @Override
    public Dimension getPreferredSize() {
        return preferredDimensions;
    }

    /*
     * Will draw the background to JPanel with anti-aliasing on and quality rendering
     */
    @Override
    protected void paintComponent(Graphics grphcs) {
        super.paintComponent(grphcs);

        //convert graphics object to graphics2d object
        Graphics2D g2d = (Graphics2D) grphcs;

        //set anti-aliasing on and rendering etc
        //GamePanel.applyRenderHints(g2d);

        //draw the image as the background
        g2d.drawImage(background, 0, 0, null);

        //g2d.dispose();//if I uncomment this no LAbels will be shown
    }
}

class PopUpJLabel extends JLabel {

    public final static Font defaultFont = new Font("Arial", Font.PLAIN, 50);
    public final static Font hoverFont = new Font("Arial", Font.BOLD, 70);

    PopUpJLabel(String text) {
        super(text);
        setHorizontalAlignment(JLabel.CENTER);
        setForeground(Color.ORANGE);
        setFont(defaultFont);

        //allow component to be focusable
        setFocusable(true);

        //add focus adapter to change fints when focus is gained or lost (used for transversing labels with keys)
        addFocusListener(new FocusAdapter() {
            @Override
            public void focusGained(FocusEvent fe) {
                super.focusGained(fe);
                if (isEnabled()) {
                    setFont(getHoverFont());
                }
            }

            @Override
            public void focusLost(FocusEvent fe) {
                super.focusLost(fe);
                setFont(getDefaultFont());
            }
        });

        addMouseListener(new MouseAdapter() {
            @Override
            public void mouseEntered(MouseEvent me) {
                super.mouseEntered(me);
                if (isEnabled()) {
                    setFont(getHoverFont());
                }
                //call for focus mouse is over this component
                requestFocusInWindow();
            }
        });

    }

    Font getDefaultFont() {
        return defaultFont;
    }

    Font getHoverFont() {
        return hoverFont;
    }
}