如何使用 JPanel 作为客户端创建动态大小的 JScrollPane？

Question

在我的代码中，用户可以使用菜单向主 JPanel 添加新按钮。 JPanel 使用 FlowLayout 表单，因此根据窗口的大小，每行上的数字或按钮会发生变化以适应最佳视图......嗯，在我介绍 JScrollPane 之前就是这种情况。现在我有两个问题：

1. 一旦用户将窗口大小重新调整为首选大小或更低，每行上的按钮数将停止更改。 *以前没有这个问题，即使设置了首选尺寸。

2. 我只能滚动查看 JPanel 首选大小范围内的按钮。任何放置在外面的东西都是不可见的，也不会增加 JScrollPane 范围的大小。

代码如下：

package testit;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Insets;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.KeyStroke;
import javax.swing.border.LineBorder;

class TestIt extends JFrame implements ActionListener {
    //Main window frame, content panel and scroll pane
    private JFrame main_frame;
    private JPanel main_panel;
    private JScrollPane main_scroll;

    //Screen size
    private Dimension screen = Toolkit.getDefaultToolkit().getScreenSize();

    public TestIt() {
        //Set up the main frame
        main_frame = new JFrame("Test Program");
        main_frame.setLayout(new BorderLayout());
        main_frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        main_frame.setIconImage(
                new ImageIcon("src/testit/resources/img/app_icon.gif").getImage());

        //Set up the content panel and add it to the scroll pane
        main_panel = new JPanel();
        main_panel.setLayout(new FlowLayout());
        main_panel.setPreferredSize(
                new Dimension(screen.width/10 * 6, screen.height/10 * 6));
        main_scroll = new JScrollPane(main_panel);

        //Add the menu bar and the scroll pane to the main frame
        main_frame.add(main_scroll, BorderLayout.CENTER);       
        main_frame.setJMenuBar(createMenuBar());

        //Display the main GUI
        main_frame.pack();
        main_frame.setLocationRelativeTo(null);
        main_frame.setVisible(true);

    }

    private JMenuBar createMenuBar() {
        //Create the top menu bar
        JMenuBar top_menu_bar = new JMenuBar();

        //Create the menu
        JMenu main_menu = new JMenu ("Menu");
        main_menu.setMnemonic(KeyEvent.VK_M);
        top_menu_bar.add(main_menu);

        //Create the menu items and add them to the menu
        JMenuItem menu_item;

        menu_item = new JMenuItem("Add New");
        menu_item.setMnemonic(KeyEvent.VK_N);
        menu_item.setAccelerator(
                KeyStroke.getKeyStroke(KeyEvent.VK_N, ActionEvent.ALT_MASK));
        menu_item.setActionCommand("new");
        menu_item.addActionListener(this);
        main_menu.add(menu_item);

        menu_item = new JMenuItem("Save");
        menu_item.setMnemonic(KeyEvent.VK_S);
        menu_item.setAccelerator(
                KeyStroke.getKeyStroke(KeyEvent.VK_S, ActionEvent.ALT_MASK));
        menu_item.setActionCommand("save");
        menu_item.addActionListener(this);
        main_menu.add(menu_item);

        menu_item = new JMenuItem("Exit");
        menu_item.setMnemonic(KeyEvent.VK_X);
        menu_item.setAccelerator(
                KeyStroke.getKeyStroke(KeyEvent.VK_X, ActionEvent.ALT_MASK));
        menu_item.setActionCommand("exit");
        menu_item.addActionListener(this);
        main_menu.add(menu_item);

        //Return the assembled menu bar
        return top_menu_bar;
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        switch (e.getActionCommand()) {
            case "new":
                createThumb();
                break;
            case "save":
                break;
            default:
                quit();
                break;
        }
    }

    private void createThumb() {
        //Width and height for the thumbnail button
        final int H = 170;
        final int W = 150;

        //Set up the thumbnail button
        ImageIcon image = new ImageIcon("src/testit/resources/img/test.gif");       
        JButton thumb = new JButton(image);
        thumb.setMargin(new Insets(0, 0, 0, 0));
        thumb.setBorder(new LineBorder(Color.BLACK));
        thumb.setBackground(Color.BLACK);
        thumb.setPreferredSize(new Dimension(W, H));
        thumb.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                openNewFrame();
            }
        });
        main_panel.add(thumb);
        main_panel.validate();
    }

    private void openNewFrame() {
        JFrame new_window = new JFrame();
        new_window.setPreferredSize(new Dimension(400, 800));
        new_window.pack();
        new_window.setLocationRelativeTo(null);
        new_window.setVisible(true);
    }

    private void quit() {
        System.exit(0);
    }

    //Create an instance of the program
    private static void runIt() {
        TestIt program = new TestIt();
    }

    public static void main(String [] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                runIt();
            }
        });
    }
}

我尝试了很多东西，并且一直在研究 Javadoc.... 我已经阅读了很多东西和教程，但仍然无法让我的滚动/调整大小起作用。

Answer 1

当您设置组件的preferredSize 时，您会固定它的大小，因此它不会在JScrollPane 中展开。一个解决方案是不这样做，不固定容纳 JButton 的容器的大小。

例如，

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;

import javax.swing.*;

@SuppressWarnings("serial")
public class TestIt2 extends JPanel {
   private static final Dimension THUMB_SIZE = new Dimension(170, 150);
   private Dimension screen = Toolkit.getDefaultToolkit().getScreenSize();
   private JPanel thumbPanel = new JPanel(new GridLayout(0, 6, 5, 5));

   public TestIt2() {
      JPanel holderPanel = new JPanel(new BorderLayout());
      holderPanel.add(thumbPanel, BorderLayout.NORTH);
      holderPanel.add(Box.createGlue(), BorderLayout.CENTER);

      setLayout(new BorderLayout());
      add(new JScrollPane(holderPanel), BorderLayout.CENTER);
   }

   public JMenuBar createMenuBar() {
      JMenuBar top_menu_bar = new JMenuBar();
      JMenu main_menu = new JMenu("Menu");
      main_menu.setMnemonic(KeyEvent.VK_M);
      top_menu_bar.add(main_menu);
      JMenuItem menu_item;

      menu_item = new JMenuItem("Add New");
      menu_item.setMnemonic(KeyEvent.VK_N);
      menu_item.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_N,
            ActionEvent.ALT_MASK));
      menu_item.setActionCommand("new");
      menu_item.addActionListener(new ActionListener() {

         @Override
         public void actionPerformed(ActionEvent arg0) {
            createThumb();
         }
      });
      main_menu.add(menu_item);


      return top_menu_bar;
   }

   protected void createThumb() {
      JButton thumb = new JButton("Thumb");
      thumb.setPreferredSize(THUMB_SIZE);
      thumbPanel.add(thumb);
      revalidate();
      repaint();
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(screen.width / 10 * 6,
            screen.height / 10 * 6);
   }

   private static void createAndShowGui() {
      TestIt2 mainPanel = new TestIt2();

      JFrame frame = new JFrame("TestIt2");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.setJMenuBar(mainPanel.createMenuBar());
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}