java - 如何将多个 JPanel 添加到 JScrollPane？

Question

我正在努力添加多个 JPanel容器到单个 JScrollPane在 Java 摆动。我想要的输出是在 JFrame 上的基本面板上有一个滚动 Pane 。 ，并且现在让滚动 Pane 包含 2 个面板。
基本上，就像滚动 Pane 可以将其 View 设置为单个面板一样，我希望将其设置为 2 个面板。
这些面板上唯一存在的东西是在它们上面绘制的图形，没有 JComponent实例。我看过其他类似的链接:Java Swing: how to add multiple JPanels to a JScrollPane ，但我没有得到想要的输出。这是我的最新尝试，它只显示滚动 Pane 边缘并且面板不可见(最小可重现):

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

public class Test {
    
    public static void main(String[] args) {
        new Test();
    }
    
    public Test() {
        JFrame frame = new JFrame("Test"); //initialize frame
        frame.setSize(500, 500);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        JPanel base = new JPanel(); //make base panel with SpringLayout
        SpringLayout baseLayout = new SpringLayout();
        base.setLayout(baseLayout);
        
        JPanel panel1 = new JPanel() { //initialize JPanels
            public void paintComponent(Graphics tool) {
                super.paintComponent(tool);
                tool.drawRect(50, 50, 100, 100);
            }
        };
        
        JPanel panel2 = new JPanel() {
            public void paintComponent(Graphics tool) {
                super.paintComponent(tool);
                tool.drawRect(75, 75, 50, 50);
            }
        };
        
        Container cont = new Container(); //create a container to hold panels
        SpringLayout contLayout = new SpringLayout();
        cont.setLayout(contLayout);
        
        contLayout.putConstraint(SpringLayout.WEST, panel1, 0, SpringLayout.WEST, cont); 
        contLayout.putConstraint(SpringLayout.NORTH, panel1, 0, SpringLayout.NORTH, cont);
        cont.add(panel1); //add panel1 to top left corner of container
        
        
        contLayout.putConstraint(SpringLayout.WEST, panel2, 0, SpringLayout.WEST, cont); 
        contLayout.putConstraint(SpringLayout.NORTH, panel2, 0, SpringLayout.NORTH, cont);
        cont.add(panel2); //add panel2 to top left corner of container
        
        cont.setPreferredSize(new Dimension(201, 201));
        
        JScrollPane scroll = new JScrollPane(cont); //add container to scroll pane
        scroll.setPreferredSize(new Dimension(200, 200));
        
        baseLayout.putConstraint(SpringLayout.HORIZONTAL_CENTER, scroll, 0, SpringLayout.HORIZONTAL_CENTER, base); 
        baseLayout.putConstraint(SpringLayout.VERTICAL_CENTER, scroll, 0, SpringLayout.VERTICAL_CENTER, base);
        base.add(scroll); //add scroll pane to center of base JPanel
        
        frame.add(base);
        frame.setVisible(true);
    }
}

Answer 1

好的，所以我做了更多的实验，我添加了这几行，现在两个面板都正确显示在 JScrollPane 中:

panel1.setPreferredSize(cont.getPreferredSize());
panel2.setPreferredSize(cont.getPreferredSize());
        
panel1.setOpaque(false);
panel2.setOpaque(false);

不知道为什么它有效，如果有人可以解释那会很棒。这是工作代码:

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

public class Test {
    
    public static void main(String[] args) {
        new Test();
    }
    
    public Test() {
        JFrame frame = new JFrame("Test"); //initialize frame
        frame.setSize(500, 500);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        JPanel base = new JPanel(); //make base panel with SpringLayout
        SpringLayout baseLayout = new SpringLayout();
        base.setLayout(baseLayout);
        
        JPanel panel1 = new JPanel() { //initialize JPanels
            public void paintComponent(Graphics tool) {
                super.paintComponent(tool);
                tool.drawRect(50, 50, 100, 100);
            }
        };
        
        JPanel panel2 = new JPanel() {
            public void paintComponent(Graphics tool) {
                super.paintComponent(tool);
                tool.drawRect(75, 75, 50, 50);
            }
        };
        
        Container cont = new Container(); //create a container to hold panels
        SpringLayout contLayout = new SpringLayout();
        cont.setLayout(contLayout);
        
        contLayout.putConstraint(SpringLayout.WEST, panel1, 0, SpringLayout.WEST, cont); 
        contLayout.putConstraint(SpringLayout.NORTH, panel1, 0, SpringLayout.NORTH, cont);
        cont.add(panel1); //add panel1 to top left corner of container
        
        contLayout.putConstraint(SpringLayout.WEST, panel2, 0, SpringLayout.WEST, cont); 
        contLayout.putConstraint(SpringLayout.NORTH, panel2, 0, SpringLayout.NORTH, cont);
        cont.add(panel2); //add panel2 to top left corner of container
        
        
        cont.setPreferredSize(new Dimension(201, 201));
        panel1.setPreferredSize(cont.getPreferredSize());
        panel2.setPreferredSize(cont.getPreferredSize());
        
        panel1.setOpaque(false);
        panel2.setOpaque(false);
        
        JScrollPane scroll = new JScrollPane(cont); //add container to scroll pane
        scroll.setPreferredSize(new Dimension(200, 200));
        
        baseLayout.putConstraint(SpringLayout.HORIZONTAL_CENTER, scroll, 0, SpringLayout.HORIZONTAL_CENTER, base); 
        baseLayout.putConstraint(SpringLayout.VERTICAL_CENTER, scroll, 0, SpringLayout.VERTICAL_CENTER, base);
        base.add(scroll); //add scroll pane to center of base JPanel
        
        frame.add(base);
        frame.setVisible(true);
    }
}