无法在ActionListener中重绘

Question

EDIT: Now it works fine, but when i switch to the "game" JPanel, the KeyListener is not working :( Any way to fix this?

i'm just programming a java game and there is a problem with the repaint() method: I wanna get from the menu to the game so i remove the menu panel and add the game panel ("Zeichnen" extends JPanel) But every time i try to repaint, eclipse gives me the following error: "The method repaint() is undefined for the type new ActionListener(){}" Can anyone please help me? :(

Code:

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;


public class Frame {

JFrame frame;
JPanel menu;
JButton start;
Zeichnen game;

public Frame() {

    start = new JButton("Start Game");
    menu = new JPanel();
    game = new Zeichnen();
    frame = new JFrame("Epic Game");

    start.addActionListener(new ActionListener () {
        public void actionPerformed(ActionEvent e) {

            frame.remove(menu);
            frame.add(game);
            repaint();

    }});

    frame.setVisible(true);
    frame.setSize(640,480);
    game.addKeyListener(new Listener(game));
    menu.add(start);
    frame.add(menu);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLocationRelativeTo(null);

}
}

Answer 1

Suggestsions:

• You should use a CardLayout to have a container swap components as you are doing since this is the easiest and most reliable way to change views. There are many examples of using this in prior questions on this site.
• Don't use a KeyListener but rather use Key Bindings since they are much more forgiving with regard to component focus.
• Rename your "Frame" class to something that doesn't match a core Java class. It is a very confusing name.

For example:

import java.awt.event.*;
import java.awt.*;

import javax.swing.*;

public class ContentPane extends JPanel {

   public static final String MENU = "menu";
   public static final String GAME = "game";
   private static final int PREF_W = 640;
   private static final int PREF_H = 480;

   private CardLayout cardlayout = new CardLayout();
   private JPanel menu = new JPanel();
   private JButton start;
   private Zeichnen game;

   public ContentPane() {
      setLayout(cardlayout);
      start = new JButton("Start Game");
      game = new Zeichnen();

      add(menu, MENU);
      add(game, GAME);

      start.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            cardlayout.next(ContentPane.this);
         }
      });

      menu.add(start);
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

   private static void createAndShowGui() {
      JFrame frame = new JFrame("Epic Game");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(new ContentPane());
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

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

And the Key Bindings:

@SuppressWarnings("serial")
class Zeichnen extends JPanel {
   private static final String DOWN = "down";

   public Zeichnen() {
      int condition = WHEN_IN_FOCUSED_WINDOW;
      InputMap inputMap = getInputMap(condition);
      ActionMap actionMap = getActionMap();

      inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0), DOWN);
      actionMap.put(DOWN, new AbstractAction(DOWN) {
         {
            putValue(ACTION_COMMAND_KEY, DOWN);
         }

         @Override
         public void actionPerformed(ActionEvent evt) {
            System.out.println(evt.getActionCommand());
         }
      });
   }
}

Answer 2

你需要调用game.repaint（），因为你创建的匿名类没有名为repaint（）的方法

Answer 3

That's because there's no method in any class in that structure (ie, the Frame → anonymous ActionListener ) that extends Component and has a repaint method.

You could either make your main Frame class extend JFrame , or call game.repaint() . You probably want to do the former.