Java GUI 类按钮面板

Question

我希望在我的 GUI 中显示一个包含 12 个按钮的面板。但出于某种原因，他们没有出现。我现在不知道我的代码有什么问题。我还没有在我的 Action 执行方法中放任何东西，但我会的(现在我只专注于让按钮显示)。那么有人可以告诉我出了什么问题吗？谢谢!

编辑* 这就是我的 GUI 类中的所有内容，我想要显示电梯对象的两个 Canvas (没有显示)

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;

public class GUI extends JFrame implements ActionListener 
{
private static final Dimension PREF_SIZE = new Dimension(1000, 1000);

MyCanvas leftCanvas = new MyCanvas();
MyCanvas rightCanvas = new MyCanvas();
ArrayList<JButton> buttonList = new ArrayList<JButton>(); 
JPanel buttonPanel, leftPanel, rightPanel;

public GUI()
{
  super("Elevators");
    //setSize(800,800);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    //setVisible(true);

    JPanel mainPanel = new JPanel();
    mainPanel.setLayout(new GridLayout(1,3));

    leftPanel = new JPanel();
    leftPanel.add(leftCanvas);
    rightPanel = new JPanel();
    rightPanel.add(rightCanvas);

    buttonPanel = new JPanel();     
    buttonPanel.setLayout(new GridLayout(12,1));   
    buttonPanel.setSize(900,900);

    add(mainPanel); 

    for(int i=0; i<12; i++)
    {
        buttonList.add(new JButton(""+i));
        JButton btn = buttonList.get(i);
        buttonPanel.add(btn);
    }
    mainPanel.add(buttonPanel, BorderLayout.CENTER);
    mainPanel.add(leftPanel, BorderLayout.EAST);
    mainPanel.add(rightPanel, BorderLayout.WEST);
    createAndShowGui();
}
@Override
public Dimension getPreferredSize() {
    return PREF_SIZE;
}
private static void createAndShowGui() {
  UI frame = new UI();
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  frame.pack();
  frame.setLocationByPlatform(true);
  frame.setVisible(true);
}
//public static void main(String[] args) {
  //SwingUtilities.invokeLater(new Runnable() {
    // public void run() {
      //  createAndShowGui();
   //  }
  //});
//} 
//public void paint(Graphics g)
//{

// }

public void actionPerformed(ActionEvent e)
{

}

}    

这是我的 Canvas 类

import java.awt.*;
import java.awt.event.*;
import javax.swing.JFrame;
import javax.swing.JButton;

public class MyCanvas extends Canvas 
{
private Elevator e;

int xPos =0;
int yPos=0;

public MyCanvas()
{
   setSize(600,600);
   repaint();
}


public void paint(Graphics g)
{
   g.setColor(Color.BLACK);
   g.fillRect(xPos,yPos,100, 100);


}

public void actionPerformed(ActionEvent e)
{
    repaint();
}
public void setElevator(Elevator ev)
{
    e = ev;
}
} 

Answer 1

您覆盖了框架的 paint 方法...

public void paint(Graphics g)
{

}

但是未能调用super.paint(g)....

paint 的职责之一是绘制子组件...

已更新

此外，调用 this.setLayout(new BorderLayout()) 会扰乱您的布局，因为约束已被丢弃，这意味着布局管理器不知道应该去哪里

更新示例

我能够制作这个...

有了这个

public class Elevator02 {

    public static void main(String[] args) {
        new Elevator02();
    }

    public Elevator02() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                UI ui = new UI();
                ui.setLocationRelativeTo(null);

            }
        });
    }

    public class UI extends JFrame implements ActionListener {

        ArrayList<Button> buttonList = new ArrayList();
        JPanel buttonPanel;

        public UI() {
            super("Elevators");
            setSize(200, 400);
            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            setVisible(true);

            JPanel mainPanel = new JPanel();
            mainPanel.setLayout(new GridLayout(1, 3));

            buttonPanel = new JPanel();
            buttonPanel.setLayout(new GridLayout(12, 1));

            add(mainPanel);

            for (int i = 0; i < 12; i++) {
                buttonList.add(new Button("" + i));
                buttonPanel.add(buttonList.get(i));
                buttonList.get(i).addActionListener(this);
            }
            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            mainPanel.add(buttonPanel);
        }

//        public void paint(Graphics g) {
//        }
        public void actionPerformed(ActionEvent e) {
        }
    }
}