如何創建一個動態大小的JScrollPane w/JPanel作爲客戶端？

Question

在我的代碼中，用戶可以使用菜單將新按鈕添加到主JPanel。 JPanel使用FlowLayout表單，以便根據窗口的大小，更改每行上的數字或按鈕以適應最佳視圖...好的，在我引入JScrollPane之前就是如此。現在我有兩個問題：

1. 只要用戶將窗口重新調整到首選大小或更低，每行上的按鈕數就會停止更改。 *以前沒有這個問題，即使設置了首選大小。

2. 我只能滾動以查看是JPanel的優選尺寸範圍內的按鈕。任何放在外面的東西都是不可查看的，並且不會增加JScrollPane範圍的大小。

下面的代碼：

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(); 
      } 
     }); 
    } 
} 

我試過很多東西，我經歷過的Javadoc挖....我讀過很多東西和教程，但還是可以我的滾動/重新調整大小工作。

Answer 1

當您設置組件的首選大小，你確定它的大小，所以它不會JScrollPane的範圍內展開。一個解決方案是不要這樣做，不要修復容納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(); 
     } 
     }); 
    } 
}