java - 在列表中组织 JPanel 的最佳方式是什么？

Question

我发现自己最近写了很多程序，它们都需要显示一些数据集合。到目前为止，我想到的最好看的方法是制作小的 JPanel，其中包含集合中每个项目的数据，并将它们全部放在一个大的 JPanel 中，然后我将其放入 JScrollPane 中。它的工作和外观都符合预期，但有一个问题:我似乎无法让较小的 JPanel 从较大的 JPanel 的顶部开始。

只有当我将少量小 JPanel(绿色)添加到较大的 JPanel(红色)中时，问题才会明显。

下面描述的是我用来生成上述内容的方法，我想知道是否有更好的方法可以做到这一点(列表应该从顶部开始):

• 我创建了一个扩展 JPanel 的类，并在其中添加了我想要显示的所有数据。我们称它为“SmallPanel.java”。我没有设置它的大小(稍后出现)。

• 在我的主窗口类(扩展 JFrame)中:

  private JScrollPane scrollPane;
  private JPanel panel;
  ...
  scrollPane = new JScrollPane();
  getContentPane().add(scrollPane);
  
  panel = new JPanel();
  panel.setLayout(new GridBagLayout());
  scrollPane.setViewportView(panel);
  ...
  private void addPanel()
  {
      GridBagConstraints gbc = new GridBagConstraints();
      gbc.gridx = 0;
      gbc.gridy = panel.getComponentCount(); //The new JPanel's place in the list
      gbc.fill = GridBagConstraints.HORIZONTAL;
      gbc.anchor = GridBagConstraints.PAGE_START; //I thought this would do it
      gbc.ipady = 130; //Set the panel's height, the width will get set to that of the container JPanel (which is what I want since I'd like my JFrames to be resizable)
      gbc.insets = new Insets(2, 0, 2, 0); //Separation between JPanels in the list
      gbc.weightx = 1.0;
      SmallPanel smallPanel = new SmallPanel();
      panel.add(smallPanel, gbc);
      panel.revalidate();
      panel.invalidate();
      panel.repaint(); //Better safe than peeved
  }
  

• 每次我想添加面板时调用 addPanel() 方法。

编辑

最终解决方案(基于下面 MadProgrammer 的回答):

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.border.BevelBorder;

public class ListPanel extends JPanel
{
    private static final long serialVersionUID = 1L;
    private JPanel fillerPanel;
    private ArrayList<JPanel> panels;

    public ListPanel(List<JPanel> panels, int height)
    {
        this(panels, height, new Insets(2, 0, 2, 0));
    }

    public ListPanel(List<JPanel> panels, int height, Insets insets)
    {
        this();
        for (JPanel panel : panels)
            addPanel(panel, height, insets);
    }

    public ListPanel()
    {
        super();
        this.fillerPanel = new JPanel();
        this.fillerPanel.setMinimumSize(new Dimension(0, 0));
        this.panels = new ArrayList<JPanel>();
        setLayout(new GridBagLayout());
    }

    public void addPanel(JPanel p, int height)
    {
        addPanel(p, height, new Insets(2, 0, 2, 0));
    }

    public void addPanel(JPanel p, int height, Insets insets)
    {
        super.remove(fillerPanel);
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridx = 0;
        gbc.gridy = getComponentCount();
        gbc.fill = GridBagConstraints.HORIZONTAL;
        gbc.anchor = GridBagConstraints.PAGE_START;
        gbc.ipady = height;
        gbc.insets = insets;
        gbc.weightx = 1.0;
        panels.add(p);
        add(p, gbc);
        gbc = new GridBagConstraints();
        gbc.gridx = 0;
        gbc.gridy = getComponentCount();
        gbc.fill = GridBagConstraints.VERTICAL;
        gbc.weighty = 1.0;
        add(fillerPanel, gbc);
        revalidate();
        invalidate();
        repaint();
    }

    public void removePanel(JPanel p)
    {
        removePanel(panels.indexOf(p));
    }

    public void removePanel(int i)
    {
        super.remove(i);
        panels.remove(i);
        revalidate();
        invalidate();
        repaint();
    }

    public ArrayList<JPanel> getPanels()
    {
        return this.panels;
    }

    public static void main(String[] args)
    {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setMinimumSize(new Dimension(500, 500));
        f.setLocationRelativeTo(null);
        f.getContentPane().setLayout(new BorderLayout());
        final ListPanel listPanel = new ListPanel();
        for (int i = 1; i <= 10; i++)
            listPanel.addPanel(getRandomJPanel(), new Random().nextInt(50) + 50);
        JButton btnAdd = new JButton("Add");
        btnAdd.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent paramActionEvent)
            {
                listPanel.addPanel(getRandomJPanel(), new Random().nextInt(50) + 50);
            }
        });
        JButton btnRemove = new JButton("Remove");
        btnRemove.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent paramActionEvent)
            {
                listPanel.removePanel(0);
            }
        });
        f.getContentPane().add(btnRemove, BorderLayout.NORTH);
        f.getContentPane().add(btnAdd, BorderLayout.SOUTH);
        JScrollPane scrollPane = new JScrollPane();
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);
        scrollPane.setViewportView(listPanel);
        f.getContentPane().add(scrollPane, BorderLayout.CENTER);
        f.setVisible(true);
    }

    public static JPanel getRandomJPanel()
    {
        JPanel panel = new JPanel();
        panel.setBorder(new BevelBorder(BevelBorder.LOWERED, null, null, null, null));
        panel.add(new JLabel("This is a randomly sized JPanel"));
        panel.setBackground(new Color(new Random().nextFloat(), new Random().nextFloat(), new Random().nextFloat()));
        return panel;
    }
}

Answer 1

我发现的最佳解决方案是使用 SwingLabs SwingX(可以从 here 下载)库中的 VerticalLayout。

您“可以”使用 GridBagLayout，在末尾放置一个不可见的组件，其 weighty 属性设置为 1，但这需要管理更多的额外工作，因为您需要不断更新所有组件的 x/y 位置以使其保持在原位...

更新了 GridBagLayout 示例

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class VerticalLayoutExample {

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

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

                final TestPane pane = new TestPane();
                JButton add = new JButton("Add");
                add.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        pane.addAnotherPane();
                    }
                });

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new JScrollPane(pane));
                frame.add(add, BorderLayout.SOUTH);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private JPanel filler;
        private int y = 0;

        public TestPane() {

            setBackground(Color.RED);
            setLayout(new GridBagLayout());

            filler = new JPanel();
            filler.setOpaque(false);
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.weighty = 1;
            gbc.gridy = 0;

            add(filler, gbc);

        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 400);
        }

        public void addAnotherPane() {

            JPanel panel = new JPanel(new GridBagLayout());
            panel.add(new JLabel("Hello"));

            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridy = y++;
            gbc.weightx = 1;
            gbc.fill = GridBagConstraints.HORIZONTAL;
            gbc.gridwidth = GridBagConstraints.REMAINDER;
            gbc.insets = new Insets(4, 4, 4, 4);

            add(panel, gbc);

            GridBagLayout gbl = ((GridBagLayout)getLayout());
            gbc = gbl.getConstraints(filler);
            gbc.gridy = y++;
            gbl.setConstraints(filler, gbc);

            revalidate();
            repaint();

        }           
    }        
}

这只是一个概念。正如 camickr 指出的那样，只要您知道最后一个组件，就可以调整组件的 GridBagConstraints 以便列表中的最后一个组件具有 weighty 1 而不是...

如您所愿，您可以覆盖 GridBagLayout 所做的一些事情，例如，我要求 GridBagLayout 代替使用面板的首选大小让它填充父容器的 HORIZONTAL 宽度...