JScrollPane不工作/显示滚动条

Question

我有一个JFrame，它包含一个JPanel，其中包含JScrollPane，其中包含另一个JPanel，与两个组件（JPanels）。 出于某种原因，当我使用WindowBuilder的预览选项来查看框架时，JScrollPane显示了滚动条水平，但是当我编译并运行应用程序时，它不会。 这里是什么样子：

从预览选项：

当它编译：

这里是我的代码：

package home; 

import java.awt.EventQueue; 

import javax.swing.JFrame; 

import java.awt.SystemColor; 

import javax.swing.JPanel; 
import javax.swing.SpringLayout; 
import javax.swing.UIManager; 

import net.miginfocom.swing.MigLayout; 

import javax.swing.JLabel; 
import javax.swing.SwingConstants; 

import java.awt.Component; 
import java.awt.BorderLayout; 
import java.awt.Frame; 

import com.jgoodies.forms.layout.FormLayout; 
import com.jgoodies.forms.layout.ColumnSpec; 
import com.jgoodies.forms.layout.RowSpec; 
import com.jgoodies.forms.factories.FormFactory; 

import javax.swing.GroupLayout; 
import javax.swing.GroupLayout.Alignment; 
import javax.swing.JButton; 
import javax.swing.LayoutStyle.ComponentPlacement; 
import javax.swing.UnsupportedLookAndFeelException; 

import java.awt.Font; 

import javax.swing.BoxLayout; 

import java.awt.event.ActionListener; 
import java.awt.event.ActionEvent; 
import java.awt.event.WindowAdapter; 
import java.awt.event.WindowEvent; 
import java.awt.Color; 
import java.awt.Dimension; 
import java.io.Serializable; 
import java.util.ArrayList; 
import java.util.List; 
import java.util.Random; 

import javax.swing.ImageIcon; 
import javax.swing.JScrollPane; 
import javax.swing.border.EtchedBorder; 
import javax.swing.border.LineBorder; 
import javax.swing.ScrollPaneConstants; 

public class AtmManeger implements Serializable { 

    private JFrame frmAtmManeger; 
    public int NumOfOpenAtmMachines = 0; 
    private final AtmManeger frame = this; 
    private ArrayList<ATMmachine> ATMs = new ArrayList<ATMmachine>();//Array list of all the ATM machines that were opened 
    private AtmAccountDataBase atmDataBase = new AtmAccountDataBase(); 
    private JLabel contLabel = null; 
    /** 
    * Launch the application. 
    */ 
    public static void main(String[] args) { 

     EventQueue.invokeLater(new Runnable() { 
      public void run() { 
       try { 
        AtmManeger window = new AtmManeger(); 
        window.frmAtmManeger.setVisible(true); 
       } catch (Exception e) { 
        e.printStackTrace(); 
       } 
      } 
     }); 

    } 

    /** 
    * Create the application. 
    */ 
    public AtmManeger getFrame() { 
     return this.frame; 
    } 
    public AtmManeger() { 
     initialize(); 
    } 

    /** 
    * Initialize the contents of the frame. 
    */ 
    private void initialize() { 
     try { 
      UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); 
     } catch (ClassNotFoundException e1) { 
      // TODO Auto-generated catch block 
      e1.printStackTrace(); 
     } catch (InstantiationException e1) { 
      // TODO Auto-generated catch block 
      e1.printStackTrace(); 
     } catch (IllegalAccessException e1) { 
      // TODO Auto-generated catch block 
      e1.printStackTrace(); 
     } catch (UnsupportedLookAndFeelException e1) { 
      // TODO Auto-generated catch block 
      e1.printStackTrace(); 
     } 
     frmAtmManeger = new JFrame(); 
     frmAtmManeger.setMinimumSize(new Dimension(615, 420)); 
     frmAtmManeger.getContentPane().setBackground(SystemColor.activeCaption); 
     JPanel mainPanel = new JPanel(); 
     mainPanel.setPreferredSize(new Dimension(10, 10)); 
     frmAtmManeger.setContentPane(mainPanel); 
     JScrollPane scrollPane = new JScrollPane(); 
     mainPanel.add(scrollPane, BorderLayout.CENTER); 
     JPanel subPanel = new JPanel(); 
     subPanel.setSize(new Dimension(1190, 350)); 
     subPanel.setBackground(SystemColor.activeCaption); 
     subPanel.setPreferredSize(new Dimension(1190, 350)); 
     scrollPane.setViewportView(subPanel); 
     subPanel.setLayout(new MigLayout("", "[50.00%,grow][50.00%,grow]", "[grow]")); 
     JPanel panel = new JPanel(); 
     subPanel.add(panel,"cell 0 0,grow"); 
     panel.setBorder(null); 
     panel.setBackground(SystemColor.textHighlight); 

     panel.setLayout(new MigLayout("", "[100.00%,grow]", "[71px][13.54%][10.09%][41px][][grow]")); 

     JPanel panel_1 = new JPanel(); 
     subPanel.add(panel_1, "cell 1 0,grow"); 
     frmAtmManeger.setTitle("ATM Maneger"); 
     frmAtmManeger.setBounds(700, 400, 609, 420); 
     frmAtmManeger.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    } 
} 

我制作了另一个与这个应用非常相似的应用，只有一个Inherents JFrame。我无法找到此代码和上面的代码之间的任何区别。代码：

package home; 

import java.awt.BorderLayout; 
import java.awt.EventQueue; 

import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.UIManager; 
import javax.swing.border.EmptyBorder; 
import javax.swing.JScrollPane; 

import java.awt.Color; 
import java.awt.FlowLayout; 

import net.miginfocom.swing.MigLayout; 

import java.awt.Dimension; 
import javax.swing.JLabel; 
import javax.swing.JButton; 

public class test02 extends JFrame { 

    private JPanel contentPane; 

    /** 
    * Launch the application. 
    */ 
    public static void main(String[] args) { 
     EventQueue.invokeLater(new Runnable() { 
      public void run() { 
       try { 
        test02 frame = new test02(); 
        frame.setVisible(true); 
       } catch (Exception e) { 
        e.printStackTrace(); 
       } 
      } 
     }); 
    } 

    /** 
    * Create the frame. 
    */ 
    public test02() { 
     try { 
      UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); 
     } catch (Exception e) { 
      // Handle exception 
     } 
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     setBounds(100, 100, 432, 300); 
     contentPane = new JPanel(); 
     contentPane.setBorder(new EmptyBorder(5, 5, 5, 5)); 
     contentPane.setLayout(new BorderLayout(0, 0)); 
     setContentPane(contentPane); 

     JScrollPane scrollPane = new JScrollPane(); 
     contentPane.add(scrollPane, BorderLayout.CENTER); 

     JPanel panel = new JPanel(); 
     panel.setPreferredSize(new Dimension(800, 220)); 
     panel.setBackground(Color.RED); 
     scrollPane.setViewportView(panel); 
     panel.setLayout(new MigLayout("", "[50.00%,grow][50.00%,grow]", "[grow]")); 

     JPanel panel_1 = new JPanel(); 
     panel.add(panel_1, "cell 0 0,grow"); 
     panel_1.setLayout(new MigLayout("", "[][][][][][][]", "[][][][][][]")); 

     JLabel lblNewLabel = new JLabel("New label"); 
     panel_1.add(lblNewLabel, "cell 2 1"); 

     JButton btnNewButton_1 = new JButton("New button"); 
     panel_1.add(btnNewButton_1, "cell 3 3"); 

     JButton btnNewButton = new JButton("New button"); 
     panel_1.add(btnNewButton, "cell 2 5"); 

     JLabel lblNewLabel_1 = new JLabel("New label"); 
     panel_1.add(lblNewLabel_1, "cell 6 5"); 

     JPanel panel_2 = new JPanel(); 
     panel.add(panel_2, "cell 1 0,grow"); 
    } 

} 

所以这可能只是一个愚蠢的错误，但它是什么？

Answer 1

我看不到您更改滚动条策略。 由于没有溢出，不更改该设置，您将看不到滚动条出现。

尝试：

scrollbar.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS); 

Answer 2

我已经写了一个程序，以显示面板按要求。

代码：

private void createUI() { 
     JFrame frame = new JFrame(); 
     JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEFT)); 
     JScrollPane pane = new JScrollPane(); 

     JPanel leftPnl = new JPanel(new BorderLayout()); 
     JPanel rightPnl = new JPanel(new BorderLayout()); 

     leftPnl.add(new JLabel("Left"), BorderLayout.CENTER); 
     leftPnl.setBorder(new LineBorder(Color.black, 5)); 
     leftPnl.setPreferredSize(new Dimension(400, 400)); 
     rightPnl.add(new JLabel("Right"), BorderLayout.CENTER); 
     rightPnl.setBorder(new LineBorder(Color.black, 5)); 
     rightPnl.setPreferredSize(new Dimension(400, 400)); 

     panel.add(leftPnl); 
     panel.add(rightPnl); 
     panel.add(pane); 

     frame.setPreferredSize(new Dimension(400, 400)); 
     frame.setTitle("ScrollPane Example"); 
     frame.add(new JScrollPane(panel)); 
     frame.setVisible(true); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    }