java为什么我不能在JFrame上“画画”？

Question

我试图利用我的JFrame，但我无法让我的super.paintComponents(g);工作。而且，当我用我的paintComponent()方法告诉它时，我的JFrame没有任何东西在起作用

以下是代码：

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

public class MTGSAMPServerReference extends JFrame implements ActionListener {

    public static Toolkit tk = Toolkit.getDefaultToolkit(); 
    static int ScrnWidth = ((int) tk.getScreenSize().getWidth());
    static int ScrnHeight = ((int) tk.getScreenSize().getHeight());
    private static final long serialVersionUID = 1L;
    private static JList list1;
    private static JButton next;

    public MTGSAMPServerReference() {
        // set flow layout for the frame
        this.getContentPane().setLayout(new FlowLayout(FlowLayout.LEADING));
        Object[]mainData = {"Vehicles", "Bikes/Bicycles", "Boats", "Houses", "Businesses", "Objects", "Jobs", "Ranks", "Licenses", "VIP"};
        JPanel controls = new JPanel(new BorderLayout(5,5));
        list1 = new JList<Object>(mainData);
        list1.setVisibleRowCount(10);
        next = new JButton("Next");
        next.addActionListener(this);
        controls.add(new JScrollPane(list1));
        controls.add(next, BorderLayout.PAGE_END);
        controls.setBorder(new EmptyBorder(25,25,0,0));
        add(controls);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getActionCommand().equals("Next")) {
            int index = list1.getSelectedIndex();
            System.out.println("Index Selected: " + index);
            String s = (String) list1.getSelectedValue();
            System.out.println("Value Selected: " + s);
        }
    }

    public void createAndShowGUI() {
        //Create and set up the window.
        JFrame f = new MTGSAMPServerReference();
        //Display the window.
        f.pack();
        f.setVisible(true);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(1200, 800);
        f.setLocationRelativeTo(null);
        list1.setSize(250, 250);
        list1.setLocation(0, 0);
        next.setSize(75, 25);
        next.setLocation(251, 276);
        MTGSAMPServerReference.this.repaint();
    }

    protected void paintComponent(Graphics g) {
        //super.paintComponent(g);  <<  Can't seem to get this to work.
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2.drawRect(0, 0, 50, 50);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
            MTGSAMPServerReference gui = new MTGSAMPServerReference();
            gui.createAndShowGUI();
            }
        });
    }
}

我以前和paintComponent()一起工作过，但似乎仍然不知道我做错了什么。我知道这必须是一个简单的解决方案，但我一辈子都找不到。有什么想法吗

感谢您的任何帮助

提前谢谢

Answer 1

paintComponent()是JPanel类的成员，而不是试图调用它的JFrame类

这就是为什么你不能打电话给super.paintComponent(Graphics g)。编译器认为您正在创建自己的完全不相关的方法，该方法碰巧也被称为paintComponent()

创建一个继承JPanel的类，并将paintComponent()方法复制粘贴到那里

就像满是评论过的鳗鱼的气垫船一样，您可以通过直接在方法头上添加@Override标记来检查您是否正确覆盖了方法；如果你收到一个错误，说明你做错了

有关JPanel和JFrame的更多信息，请参阅我对this question的回答