Adding JPanels to JScrollPane

Question

I\'m trying to show multiple smaller JPanel on a JScrollPane. To achieve this I currently add them to another JPanel and set this pane

Answer 1

To achieve this I currently add them to another JPanel and set this panel as the viewport of the scrollPane.

Not quite. You would not make the container JPanel the viewport but rather the viewport's view. The viewport itself is a very specialized container with its own layout manager, and this would be messed up if you simply replaced it with a JPanel.

i.e.,

JViewport viewport = myScrollPane.getViewport();
viewport.setView(myContainerJPanel);

or more concisely

myScrollPane.setViewportView(myContainerJPanel);

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Note that this worries me: x.setLocation(0, 45 *i); and suggests use of null layouts somewhere. Whatever you do, don't do this, don't use null layouts, especially within JScrollPanes as it will muck it all up.

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For more detailed help, consider creating and posting an sscce or a minimal example program/mcve where you condense your code into the smallest bit that still compiles and runs, has no outside dependencies (such as need to link to a database or images), has no extra code that's not relevant to your problem, but still demonstrates your problem. Also consider posting an image of your desired output.

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For example:

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridBagLayout;
import java.awt.GridLayout;

import javax.swing.*;

public class ScrollPaneEg extends JPanel {
   private static final int PREF_W = 480;
   private static final int PREF_H = PREF_W;

   public ScrollPaneEg() {
      JScrollPane scrollPane = new JScrollPane();
      scrollPane.setViewportBorder(null);
      scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);

      JPanel container = new JPanel(new GridLayout(0, 1)); // 1 column variable
                                                           // number of rows
      for (int i = 0; i < 15; i++) {
         SingleClientPanel x = new SingleClientPanel(String.valueOf(i + 1));
         // x.setLocation(0, 45 *i);
         container.add(x);
      }
      scrollPane.setViewportView(container);

      setLayout(new BorderLayout());
      add(scrollPane, BorderLayout.CENTER);
   }

   @Override
   public Dimension getPreferredSize() {
      if (isPreferredSizeSet()) {
         return super.getPreferredSize();
      }
      return new Dimension(PREF_W, PREF_H);
   }

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

      JFrame frame = new JFrame("ScrollPaneEg");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

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

class SingleClientPanel extends JPanel {
   private static final int PREF_H = 60;

   public SingleClientPanel(String text) {
      setBorder(BorderFactory.createTitledBorder("Single Client"));
      setLayout(new GridBagLayout());
      add(new JLabel("Panel: " + text, SwingConstants.CENTER));
   }

   @Override
   public Dimension getPreferredSize() {
      Dimension superSz = super.getPreferredSize();
      if (isPreferredSizeSet()) {
         return superSz;
      }
      int prefH = Math.max(superSz.height, PREF_H);
      return new Dimension(superSz.width, prefH);
   }
}

---

Also, consider using a JTable to display your tabular data. For instance,...

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Window;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;
import javax.swing.*;
import javax.swing.border.LineBorder;
import javax.swing.table.AbstractTableModel;

public class ClientOverviewTest {
   private static void createAndShowGui() {
      ClientOverviewPanel2 mainPanel = new ClientOverviewPanel2();

      JFrame frame = new JFrame("ClientOverviewPanel");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

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

}

class ClientOverviewPanel2 extends JPanel {
   private static final int CLIENTS = 5;
   private static final int PREF_W = 600;
   private static final int PREF_H = 200;
   private ClientTableModel model = new ClientTableModel();
   private JTable table = new JTable(model);

   public ClientOverviewPanel2() {
      for (int i = 0; i < CLIENTS; i++) {
         String ip = "127.000.000.001";
         UUID uuid = UUID.randomUUID();
         boolean isLocal = true;
         SingleClient client = new SingleClient(ip, uuid, isLocal);
         model.addRow(client);
      }

      table.getColumnModel().getColumn(1).setPreferredWidth(150); //!!
      table.setPreferredScrollableViewportSize(table.getPreferredSize());

      JScrollPane scrollPane = new JScrollPane(table);
      scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

      setLayout(new BorderLayout());
      add(scrollPane, BorderLayout.CENTER);
      add(new JButton(new OkAction("OK")), BorderLayout.PAGE_END);

   }

   @Override
   public Dimension getPreferredSize() {
      Dimension superSz = super.getPreferredSize();
      if (isPreferredSizeSet()) {
         return superSz;
      }
      int prefW = PREF_W;
      int prefH = Math.min(superSz.height, PREF_H);
      return new Dimension(prefW, prefH);
   }


   private class OkAction extends AbstractAction {
      public OkAction(String name) {
         super(name);
         int mnemonic = (int) name.charAt(0);
         putValue(MNEMONIC_KEY, mnemonic);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         Component source = (Component) e.getSource();
         Window window = SwingUtilities.getWindowAncestor(source);
         if (window != null) {
            window.dispose();
         }
      }
   }
}

class ClientTableModel extends AbstractTableModel {
   public final static String[] COLUMNS = { "IP", "UUID", "Local" };
   private List<SingleClient> clientList = new ArrayList<>();

   @Override
   public int getColumnCount() {
      return COLUMNS.length;
   }

   @Override
   public int getRowCount() {
      return clientList.size();
   }

   @Override
   public String getColumnName(int column) {
      return COLUMNS[column];
   }

   public void addRow(SingleClient client) {
      clientList.add(client);
      int index = clientList.size() - 1;
      fireTableRowsInserted(index, index);
   }

   @Override
   public Object getValueAt(int rowIndex, int columnIndex) {
      if (rowIndex >= getRowCount() || rowIndex < 0) {
         String text = "for rowIndex: " + rowIndex;
         throw new IllegalArgumentException(text);
      }
      if (columnIndex < 0 || columnIndex >= COLUMNS.length) {
         String text = "for columnIndex: " + columnIndex;
         throw new IllegalArgumentException(text);
      }
      SingleClient client = clientList.get(rowIndex);
      switch (columnIndex) {
      case 0:
         return client.getIp();
      case 1:
         return client.getUuid();
      case 2:
         return client.isLocal();
      }
      return null;
   }

   @Override
   public Class<?> getColumnClass(int columnIndex) {
      if (columnIndex < 0 || columnIndex >= COLUMNS.length) {
         String text = "for columnIndex: " + columnIndex;
         throw new IllegalArgumentException(text);
      }

      switch (columnIndex) {
      case 0:
         return String.class;
      case 1: 
         return UUID.class;
      case 2:
         return Boolean.class;
      }

      // default value
      return super.getColumnClass(columnIndex);
   }

   @Override
   public boolean isCellEditable(int rowIndex, int columnIndex) {
      return columnIndex == 2;
   }

   @Override
   public void setValueAt(Object aValue, int rowIndex, int columnIndex) {
      SingleClient client = clientList.get(rowIndex);
      switch (columnIndex) {
      case 0:
         break;
      case 1:
         break;
      case 2:
         boolean isLocal = (boolean) aValue; 
         client.setLocal(isLocal);

      default:
         break;
      }
   }
}

class SingleClient {
   private String ip;
   private UUID uuid;
   private boolean isLocal;

   public SingleClient(String ip, UUID uuid2, boolean isLocal) {
      this.ip = ip;
      this.uuid = uuid2;
      this.isLocal = isLocal;
   }

   public String getIp() {
      return ip;
   }

   public void setIp(String ip) {
      this.ip = ip;
   }

   public UUID getUuid() {
      return uuid;
   }

   public void setUuid(UUID uuid) {
      this.uuid = uuid;
   }

   public boolean isLocal() {
      return isLocal;
   }

   public void setLocal(boolean isLocal) {
      this.isLocal = isLocal;
   }

   @Override
   public int hashCode() {
      final int prime = 31;
      int result = 1;
      result = prime * result + ((ip == null) ? 0 : ip.hashCode());
      result = prime * result + ((uuid == null) ? 0 : uuid.hashCode());
      return result;
   }

   @Override
   public boolean equals(Object obj) {
      if (this == obj)
         return true;
      if (obj == null)
         return false;
      if (getClass() != obj.getClass())
         return false;
      SingleClient other = (SingleClient) obj;
      if (ip == null) {
         if (other.ip != null)
            return false;
      } else if (!ip.equals(other.ip))
         return false;
      if (uuid == null) {
         if (other.uuid != null)
            return false;
      } else if (!uuid.equals(other.uuid))
         return false;
      return true;
   }

}

Answer 2

Thanks to the help I was able to get it working. I'll just add my solution including changes for reference and further comments:

public class SingleClientPanel extends JPanel
{
    private JTextField ipTextfield;
    private JTextField uuidTextField;
    public SingleClientPanel()
    {
        this("127.000.000.001",UUID.randomUUID().toString(),true);
    }
    public SingleClientPanel(String ip, String uuid,boolean isLocal) 
    {
        /*
        removed: 
        setSize(new Dimension(440, 35));
        setPreferredSize(new Dimension(440, 35));
        setMaximumSize(new Dimension(440, 35));
        setMinimumSize(new Dimension(440, 35));*/
        setBorder(new LineBorder(new Color(0, 0, 0), 1, true));
        setLayout(new BoxLayout(this, BoxLayout.X_AXIS));       // added this

        ipTextfield = new JTextField();
        ipTextfield.setHorizontalAlignment(SwingConstants.CENTER);
        ipTextfield.setAlignmentX(Component.LEFT_ALIGNMENT);
        ipTextfield.setFocusable(false);
        ipTextfield.setEditable(false);
        add(ipTextfield);
        ipTextfield.setColumns(15);
        ipTextfield.setText(ip);

        uuidTextField = new JTextField();
        uuidTextField.setHorizontalAlignment(SwingConstants.CENTER);
        uuidTextField.setEditable(false);
        uuidTextField.setFocusable(false);
        add(uuidTextField);
        uuidTextField.setColumns(30);
        uuidTextField.setText(uuid);

        JButton button = new JButton(">");
        button.setEnabled(!isLocal);
        add(button);
        this.revalidate();
    }
}

public class ClientOverviewPanel extends JPanel
{
    public ClientOverviewPanel()
    {
        setLayout(new BorderLayout(0, 0));

        JButton btnOk = new JButton("Ok");
        btnOk.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent arg0)
            {
                 Window x = SwingUtilities.getWindowAncestor(ClientOverviewPanel.this);
                 if(x != null) x.dispose();
            }
        });
        add(btnOk, BorderLayout.SOUTH);

        JScrollPane scrollPane = new JScrollPane();
        /*
        removed: 
        scrollPane.setPreferredSize(new Dimension(480, 480));
        scrollPane.setSize(new Dimension(480, 480));
        scrollPane.setMinimumSize(new Dimension(480, 40));*/
        scrollPane.setViewportBorder(null);
        scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);

        Box box = new Box(BoxLayout.PAGE_AXIS);  //added

        for (int i=0; i<5;i++)
        {
            SingleClientPanel cpan = new SingleClientPanel();
            //cpan.setLocation(0, 45 *i);  removed  
            box.add(cpan);      //changed
        }

        scrollPane.setViewportView(box);    //changed
        add(scrollPane, BorderLayout.CENTER);
        this.revalidate();
    }
}