将JPanel添加到JPanel时，第一个JPanel的大小变小

Question

我真的对此感到困惑。我在做“微旅行”游戏。这是手机游戏，但我是为电脑制作的。我有一个扩展JPanel的背景类，它只绘制一个从0开始的矩形，并且有屏幕的大小（我的游戏是全屏）。我有一个主菜单类，它也扩展了JPanel。我想在那里添加主菜单的所有内容。然后，我将所有内容添加到扩展JFrame的GameFrame类中。我有一个main类，它只是调用GameFrame类。下面是我的代码：背景类：

import java.awt.*;
import javax.swing.*;

@SuppressWarnings("serial")

public class Background extends JPanel{

    int width, height;
    Color backgroundBlue;

    public Background(int width, int height){

        this.width = width;
        this.height = height;
        backgroundBlue = new Color(25, 159, 229);

    }

    @Override

    protected void paintComponent(Graphics g){
        super.paintComponent(g);
        g.setColor(backgroundBlue);
        g.fillRect(0, 0, this.width, this.height);
    }

}

MainMenu类：

import javax.swing.*;

@SuppressWarnings("serial")

public class MainMenu extends JPanel{

    Background background;

    public MainMenu(int WW, int WH){
        //WW = window width
        //WH = widow height
        this.setLocation(0, 0);
        this.setSize(WW, WH);
        background = new Background(WW, WH);
        this.add(background);
    }

}

import main_menu.MainMenu;
import main_menu.*;

import java.awt.Dimension;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.Toolkit;

import javax.swing.JFrame;

import java.awt.event.*;

@SuppressWarnings("serial")

public class GameFrame extends JFrame{

    private GraphicsDevice vc;
    private MainMenu mainMenu;
    //private Background background;

    public GameFrame(){

        Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
        mainMenu = new MainMenu((int)screenSize.getWidth(), (int) screenSize.getHeight());
        /*background = new Background((int)screenSize.getWidth(), (int) screenSize.getHeight());*/
        GraphicsEnvironment e = GraphicsEnvironment.getLocalGraphicsEnvironment();
        vc= e.getDefaultScreenDevice();
        this.setTitle("Mictrotrip");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setBounds(0, 0, (int)screenSize.getWidth(), (int)screenSize.getHeight());
        this.add(mainMenu);
        //this.add(background);
        this.setLocationRelativeTo(null);
        this.setUndecorated(true);
        this.setResizable(false);
        vc.setFullScreenWindow(this);
        addKeyListener(new KeyListener(){

            public void keyPressed(KeyEvent e){

                if(e.getKeyCode() == KeyEvent.VK_ESCAPE){
                    System.exit(0);
                }

            }

            public void keyReleased(KeyEvent e){

            }

            public void keyTyped(KeyEvent e){

            }

        });
    }

}

public class Main {

    public static void main(String[] args) {

        new GameFrame();

    }

}

Answer 1

如果希望background填充main menu，那么MainMenu的问题就在这里--您让JPanel使用缺省的FlowLayouts，而FlowLayouts将不考虑组件大小（因此Jamal的解决方案不起作用），而是考虑其首选的大小。如果您希望background填充主菜单，那么给MainMenu一个BorderLayout，然后添加您的背景组件BorderLayout.Center：

public MainMenu(int WW, int WH){
    // WW = window width
    // WH = widow height
    // this.setLocation(0, 0);
    // this.setSize(WW, WH);

    setLayout(new BorderLayout());
    background = new Background(WW, WH);
    this.add(background, BorderLayout.CENTER);
}