我的JFrame沒有改變按下按鍵

Question

我有一個Jframe設置在一個計時器上，我試圖通過按下向下鍵（特殊代碼40）來改變其中一個圖片，但沒有任何事情發生。

import javax.swing.JFrame; 
import javax.swing.*; 

import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import java.awt.*; 
import java.awt.image.BufferedImage; 

public class MenuScreen extends JFrame { 
private static JFrame frame; 
GameKeyboard GK; 

boolean gamePlay = false; 
boolean gameQuit = false; 
boolean gameTwoPlayer = false; 
String option; 

//set dimension of window and buttons 
public final int screenWidth = 800; // Width of window 
public final int screenHeight = screenWidth/12 * 9; // Height of window 

private static Graphics gr; 

//store images 
private static Image background; 
private static Image play; 
private static Image twoPlayer; 
private static Image quit; 
private static Image playSelected; 
private static Image twoPlayerSelected; 
private static Image quitSelected; 

public MenuScreen() { 
    frame = new JFrame(); 
    setSize(screenWidth, screenHeight); 

    //   frame.pack(); 
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    frame.setVisible(true); 
    frame.setResizable(false); 
    frame.setExtendedState(JFrame.MAXIMIZED_BOTH); 
    frame.setTitle("Space Wars Menu"); 
    frame.setLocation(0, 0); 


    BufferedImage canvas=new BufferedImage(920,720,BufferedImage.TYPE_INT_ARGB); 

    gr=canvas.getGraphics(); 

    JLabel label=new JLabel(new ImageIcon(canvas)); 
    frame.add(label); 

    MenuKeyboard.initialise(); 

    //load images 
    background = GameImage.loadImage("Images//background.jpg"); 
    play = GameImage.loadImage("Images//play.png"); 
    playSelected = GameImage.loadImage("Images//playSelected.png"); 
    twoPlayer = GameImage.loadImage("Images//twoPlayer.png"); 
    twoPlayerSelected = GameImage.loadImage("Images//twoPlayerSelected.png"); 
    quit = GameImage.loadImage("Images//quit.png"); 
    quitSelected = GameImage.loadImage("Images//quit.png"); 

    //draw images 
    gr.drawImage(background, 0, 0, null); 
    gr.drawImage(playSelected, 180, -50, null); 
    gr.drawImage(twoPlayer, 180, 50, null); 
    gr.drawImage(quit, 180, 150, null); 

    ActionListener taskPerformer = new ActionListener()  
     { 
      public void actionPerformed(ActionEvent evt) 
      { 
       doTimerAction(); 
      } 
     }; 
    Timer t = new Timer(25, taskPerformer); 
    t.start(); 
} 

private static void doTimerAction() { 

    int specialKey = MenuKeyboard.getSpecialKey(); 

    if (specialKey == 40) //if down pressed 
    { 
     gr.drawImage(twoPlayerSelected, 160, 150, null); 
     gr.drawImage(play, 160, -50, null); 

    } 

    } 

} 

然而，當我像添加額外的代碼：

if (specialKey == 40) //if down pressed 
    { 

     gr.drawImage(twoPlayerSelected, 160, 150, null); 
     gr.drawImage(play, 160, -50, null); 

     Game game = new Game(); 
     game.start(); 

    } 

，然後按下運行它時它即可工作，並送我到我的遊戲類！

任何人有任何建議嗎？

Answer 1

閱讀我在上一個問題中提供給您的Key Bindings link（這裏再次提供），因爲在這種情況下，使用這種方法效果最佳。計時器用於重複操作，這不是你想要做的。您需要回復事件，關鍵綁定將幫助您做到這一點。

例如：

import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.Font; 
import java.awt.GridBagLayout; 
import java.awt.event.ActionEvent; 
import java.awt.event.KeyEvent; 

import javax.swing.*; 

public class MenuScreen2 extends JPanel { 
    private static final int PREF_W = 800; 
    private static final int PREF_H = (9 * PREF_W)/12; 
    private JLabel label = new JLabel("", SwingConstants.CENTER); 

    public MenuScreen2() { 
     setLayout(new GridBagLayout()); 
     add(label); 
     label.setFont(label.getFont().deriveFont(Font.BOLD, 50)); 
     setBackground(Color.cyan); 

     // Key Bindings is done in the code below 
     // the down String will be used to tie the down keystroke put into the InputMap 
     // with the DownAction put into the ActionMap 
     String down = "down"; 
     getInputMap().put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0), down); 
     getActionMap().put(down, new DownAction()); 
    } 

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

    // This is the Action used in our Key Bindings 
    private class DownAction extends AbstractAction { 
     @Override 
     public void actionPerformed(ActionEvent arg0) { 
     label.setText("Time To Start The Game!"); 
     } 
    } 

    public static void main(String[] args) { 
     // run our Swing application in a thread-safe way 
     SwingUtilities.invokeLater(new Runnable() { 
     public void run() { 
      MenuScreen2 mainPanel = new MenuScreen2(); 

      JFrame frame = new JFrame("Menu Screen"); 
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
      frame.getContentPane().add(mainPanel); 
      frame.pack(); 
      frame.setLocationByPlatform(true); 
      frame.setVisible(true); 
     } 
     }); 
    } 
}