java - 为什么在此程序中的任何时候都没有调用 Paint() 方法？

Question

这是我正在开始制作的益智游戏的代码。我试图让它在屏幕中间显示“已暂停”，但无法使其正常工作。事实证明，即使使用各种 repaints()，也没有发生任何事情。为什么？是因为类本身实际上并没有扩展 JPanel 或 JFrame 吗？

package main;

import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class PuzzleSquares implements ActionListener, KeyListener, Runnable {
boolean running = false;
boolean inGame = false;
boolean paused = false;

JFrame frame = new JFrame();
JPanel menu = new JPanel();
JPanel game = new JPanel();

Thread thread;

public PuzzleSquares() {    
    frame.requestFocus();
    frame.setSize(500, 500);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setTitle("Just another puzzle game");

    addMenu();

    frame.setLocationRelativeTo(null);
    frame.setResizable(false);
    frame.setVisible(true);
}

public void addMenu() {
    menu.setLayout(new BoxLayout(menu, BoxLayout.Y_AXIS));
    menu.setFocusable(true);
    menu.setBackground(Color.GRAY);

    createButton("START", menu);
    createButton("HIGH SCORES", menu);
    createButton("EXIT", menu);

    frame.revalidate();
    frame.add(menu);
}

public void addGame() {
    game.setBackground(Color.GREEN);
    game.addKeyListener(this);
    game.setFocusable(true);
    game.setPreferredSize(frame.getMaximumSize());

    frame.add(game);
    frame.revalidate();
    game.requestFocus();
}

public void createButton(String title, Container c) {
    JButton button = new JButton(title) {
        {
            setSize(200, 30);
            setMaximumSize(getSize());
        }
    };
    button.setAlignmentX(JPanel.CENTER_ALIGNMENT);
    button.addActionListener(this);
    button.setActionCommand(title);

    c.add(button);
}

public synchronized void start() {
    if (running) { return; }

    running = true;

    thread = new Thread(this);
    thread.start();
}

public synchronized void stop() {
    if (!running) { return; }

    running = false;

    try { thread.join(); } catch (Exception e) {}
}

@Override
public void run() {
    while (running) {

    }
}

public void paint(Graphics g) {
    System.out.println("Hi");
    if (paused) {
        g.setColor(Color.BLACK);
        for (int i=0;i<100;i++) {
            g.drawLine(i, i+1, i, i+1);
        }
    }
}

@Override
public void actionPerformed(ActionEvent e) {
    if (e.getActionCommand().equals("START")) {
        System.out.println("Start");
        frame.remove(menu);
        addGame();
    }
    if (e.getActionCommand().equals("HIGH SCORES")) {
        System.out.println("High Scores");
    }
    if (e.getActionCommand().equals("EXIT")) {
        System.out.println("Exit");
    }
}

@Override
public void keyTyped(KeyEvent e) {

}

@Override
public void keyPressed(KeyEvent e) {
    if (e.getKeyCode() == KeyEvent.VK_ESCAPE) {
        if (!paused) {
            System.out.println("Pause");
            paused = true;
        } else {
            paused = false;
        }
        game.repaint();
    }

}

@Override
public void keyReleased(KeyEvent e) {

}

public static void main(String[] args) {
    PuzzleSquares ps = new PuzzleSquares();
    ps.start();
}
}

Answer 1

基本上，您的类是不可绘制的，它不会扩展框架可以绘制的任何内容(例如 JComponent 或 JPanel)

如果您尝试做类似的事情...

@Override
public void paint(Graphics g) {
    super.paint(g);
    System.out.println("Hi");
    if (paused) {
        g.setColor(Color.BLACK);
        for (int i=0;i<100;i++) {
            g.drawLine(i, i+1, i, i+1);
        }
    }
}

它无法编译，因为该方法不会重写其父类或接口(interface)中的任何方法。

参见Painting in AWT and Swing和 Performing Custom Painting了解更多详情

我也不鼓励使用 KeyListener 并建议使用键绑定(bind) API，请参阅 How to Use Key Bindings 。它将帮助解决您的注意力问题