如何将多个 JPanel 添加到 JScrollPane？

Question

我正在努力将多个 JPanel 容器添加到 Java swing 中的单个 JScrollPane。我想要的输出是在 JFrame 上的基础面板上有一个滚动窗格，并且现在让该滚动窗格包含 2 个面板。

基本上，就像滚动窗格可以将其视图设置为单个面板一样，我想将它设置为 2 个面板。

这些面板上唯一存在的是在其上绘制的图形，没有 JComponent 个实例。我查看了其他类似链接：Java Swing: how to add multiple JPanels to a JScrollPane，但没有获得所需的输出。这是我最近的尝试，它只显示滚动窗格边缘并且面板不可见（最小可重现性）：

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

好吧，所以我做了更多的实验并添加了这几行，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);

不确定为什么会起作用，如果有人能解释一下就好了。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);
    }
}

如何将多个 JPanel 添加到 JScrollPane？

How to add multiple JPanels to a JScrollPane?

java

swing

jpanel

jscrollpane