java - 在一个 JPanel 中包含的多个 JPanel 中绘图

Question

我有一个扩展 JPanel 的类，其中包含 3 个其他面板。我想画成 3 个面板。这就是我的代码必须是什么样的，我做错了什么？执行后我只有一个空框架。

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;


public class Thumbnail extends JPanel {

    private JPanel bigPanel;
    private JPanel panelOne;
    private JPanel panelTwo;
    private JPanel panelThree;

    public Thumbnail() {

        panelOne = new JPanel() {
            public void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.setColor(Color.black);
                g.drawString("writing something", 10, 10);
                g.drawRect(10, 10, 50, 50);
            }
        };
        bigPanel = new JPanel();
        bigPanel.add(panelOne);
        this.setLayout(new FlowLayout(FlowLayout.LEFT));
        this.add(bigPanel);
        //other codes...
    }

    public static void main(String[] args) {
        JFrame jf = new JFrame();
        Thumbnail tb = new Thumbnail();
        jf.add(tb);
        jf.pack();
        jf.setVisible(true);
    }
}

Answer 1

panelOne 不向布局管理器提供任何布局信息，这意味着默认情况下，它的首选大小为 0x0

尝试添加类似...

@Override
public Dimension getPreferredSize() {
    return new Dimension(100, 100);
}

到panelOne...

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Thumbnail extends JPanel {

    private JPanel bigPanel;
    private JPanel panelOne;
    private JPanel panelTwo;
    private JPanel panelThree;

    public Thumbnail() {

        panelOne = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.setColor(Color.black);
                g.drawString("writing something", 10, 10);
                g.drawRect(10, 10, 50, 50);
            }

            @Override
            public Dimension getPreferredSize() {
                return new Dimension(100, 100);
            }

        };
        bigPanel = new JPanel();
        bigPanel.add(panelOne);
        this.setLayout(new FlowLayout(FlowLayout.LEFT));
        this.add(bigPanel);
        //other codes...
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }
                JFrame jf = new JFrame();
                jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                Thumbnail tb = new Thumbnail();
                jf.add(tb);
                jf.pack();
                jf.setLocationRelativeTo(null);
                jf.setVisible(true);
            }
        });
    }
}

您可能想看看 Initial Threads和 Laying Out Components Within a Container了解更多详情