Problem refreshing a panel

[Mike Lipay]

Ok, I have a problem with classes working together. Here's how they are to work:

The main application (AutoHistory.java) builds a JPanel that includes a combobox which is built from the contents of a file. One button on the panel (Add Vehicle) is to add a new entry to the combobox, when this button is clicked it calls a second class (AddVehicle.java).

The second class builds a JPanel that includes several fields needed to create a new entry in the file. After adding the new entries a button is clicked (Cancel) to return to the main application.

Now, here is where I am experiencing the problem, how do I redraw the first JPanel so that the file is re-read and the combobox is updated? The main application is rather large, so I am going to try and provide a URL to a temporary file on my server, here's hoping it works.

(Please do not comment on the sloppyness of the code, I am just learning and this is still a work in process. Once it is working I intend to go back and clean things up.)

main application

second class

[Michael Dunn]

> how do I redraw the first JPanel so that the file is re-read and the combobox is updated?

you don't need to redraw the first panel.

create a method to read the file into a DefaultComboBoxModel (dcbm), and after file is closed, set the comboBox's model to that dcbm.
you call this method when the first panel is created/shown.
you can call this method again after the file changes (add/modify/delete)

[pete stein]

Suggestions:

1) I would not have the add vehicle window interact with your database. Instead have the main class deal with it and just have the add vehicle class create a vehicle object and deliver it to the main class. The database code also should be kept distinct from the GUI code if at all possible. I am no database expert, so take my recommendations here with a bit of salt.
2) Don't make the add vehicle window another JFrame, but instead make it a modal JDialog. This way your main class that calls it will know precisely when the user closes the window and will thus know when it can extract the vehicle information from it. Or you could simply place a JPanel into a JOptionPane and show it as JOptionPanes will give return constants corresponding to which button was pressed and are pretty easy to use.
3) Give the add vehicle class public getter methods so that the main class can extract information from it if the user presses the save button. You can also give it a save boolean variable so that you'll know whether or not the save button was pressed.
4) Get rid of all your static modifiers, except for the main method that is.
5) Go through the Swing layout manager tutorial so you can move away from using absolute layouts.
6) Use a DefaultComboBoxModel as your combo box's model. Then when you want to update the combobox, simply add or remove from the model, and the combobox will show these changes.

Here's a simple example of use of a JDialog to get information from the user, and then places it into a combobox. The dialog has only one JTextField for simplicity here:

AutoHistory2.java

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class AutoHistory2 {
   private static final String[] VEHICLE_NAMES = {
      "Honda", "Toyota", "Ford", "Nissan", "Cadillac", "Acura"
   };
   // this model is the "heart" of the combo box
   private DefaultComboBoxModel comboModel = new DefaultComboBoxModel();
   private JComboBox vehicleCombo = new JComboBox(comboModel);
   private JPanel mainPanel = new JPanel();
   
   public AutoHistory2() {
      JButton addVehicleBtn = new JButton("Add Vehicle");
      // actionlisteners here will be an anonymous inner class
      // whose actionPeformed method will call a private class method
      addVehicleBtn.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            addVehicleBtnActionPerformed();
         }
      });
      JButton removeVehicleBtn = new JButton("Remove Vehicle");
      removeVehicleBtn.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            removeVehicleBtnActionPerformed();
         }
      });
      JButton saveChangesBtn = new JButton("Save Changes");
      saveChangesBtn.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            saveChangesActionPerformed();
         }
      });
      JButton exitBtn = new JButton("Exit");
      exitBtn.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            exitBtnActionPerformed();
         }
      });

      // create the JPanel that holds the buttons
      JPanel buttonPanel = new JPanel(new FlowLayout(FlowLayout.LEFT, 0, 0));
      buttonPanel.add(addVehicleBtn);
      // add buttons and some gaps between buttons
      int btnPanelGap = 4;
      buttonPanel.add(Box.createHorizontalStrut(btnPanelGap));
      buttonPanel.add(removeVehicleBtn);
      buttonPanel.add(Box.createHorizontalStrut(btnPanelGap));
      buttonPanel.add(saveChangesBtn);
      buttonPanel.add(Box.createHorizontalStrut(btnPanelGap));
      buttonPanel.add(exitBtn);
      
      // put the VEHICLE_NAMES Strings into the combo box model
      for (String vName : VEHICLE_NAMES) {
         comboModel.addElement(vName);
      }
      
      // set max size so it will behave nicely with BoxLayout
      Dimension vSize = vehicleCombo.getPreferredSize();
      vehicleCombo.setMaximumSize(new Dimension(3000, vSize.height));
      
      // set up and fill our main panel.  first give it an empty border
      int borderGap = 10;
      mainPanel.setBorder(BorderFactory.createEmptyBorder(borderGap, borderGap, borderGap, borderGap));
      
      // next give it a BoxLayout oriented along the page axis
      mainPanel.setLayout(new BoxLayout(mainPanel, BoxLayout.PAGE_AXIS));
      // add our components to main as well as a vertical gap.
      int mainPanelGap = 5;
      mainPanel.add(buttonPanel);
      mainPanel.add(Box.createVerticalStrut(mainPanelGap));
      mainPanel.add(vehicleCombo);
      mainPanel.add(Box.createVerticalGlue());
   }

   // our button action performed methods
   private void addVehicleBtnActionPerformed() {
      
      // create an AddVehicle2 class (see below)
      AddVehicle2 addVeh2 = new AddVehicle2();
      
      // extract the current JFrame
      JFrame frame = (JFrame) SwingUtilities.getWindowAncestor(mainPanel);
      
      // create a new JDialog object with modal set to "true"
      JDialog dialog = new JDialog(frame, "Add Vehicle", true);
      
      // get the main jpanel from addVeh2 and add it to dialog's contentPane
      dialog.getContentPane().add(addVeh2.getMainPanel());
      dialog.pack();
      dialog.setLocationRelativeTo(null);

      // call set visible is true. since this is modal. this code will stop here
      // until the dialog has been closed
      dialog.setVisible(true);

      // this will resume only after the jdialog has been closed
      // we can no query the addVeh2 object as to its state
      // and thereby extract information from it 
      if (addVeh2.isSave()) {  // has save button been pressed
         // if so get the text from addVeh2's JTextField and add it 
         // to our combobox's model
         comboModel.addElement(addVeh2.getVehicleText());
      }
   }

   private void removeVehicleBtnActionPerformed() {
      // find the selected item in the combobox
      int index = vehicleCombo.getSelectedIndex();
      if (index >= 0) { // if item is selected
         // remove it
         comboModel.removeElementAt(index);
      }
   }

   private void saveChangesActionPerformed() {
      // TODO Code to save to database
   }

   private void exitBtnActionPerformed() {
      // extract the enclosing JFrame which inherits from Window
      Window win = SwingUtilities.getWindowAncestor(mainPanel);
      win.dispose(); // and call dispose on it
   }

   /**
    * exposes the main JPanel so it can be placed into GUIs.
    * @return
    */
   public JPanel getMainPanel() {
      return mainPanel;
   }
   
   private static void createAndShowUI() {
      JFrame frame = new JFrame("AutoHistory2");
      frame.getContentPane().add(new AutoHistory2().getMainPanel());
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      java.awt.EventQueue.invokeLater(new Runnable() {
         public void run() {
            createAndShowUI();
         }
      });
   }
}

AddVehicle2.java

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

/**
 * goal is to create a JPanel that can be placed into a JDialog
 * and can be used to get new vehicle information from the user
 * which can be added to the calling app
 * @author Pete
 *
 */
class AddVehicle2 {
   private JPanel mainPanel = new JPanel();
   private JTextField vehicleField = new JTextField(15);
   private boolean save = false;

   public AddVehicle2() {
      vehicleField.addActionListener(new SaveAction());
      JPanel textPanel = new JPanel(new FlowLayout(FlowLayout.LEFT));
      textPanel.add(new JLabel("Vehicle:"));
      textPanel.add(Box.createHorizontalStrut(5));
      textPanel.add(vehicleField);

      JButton saveBtn = new JButton(new SaveAction());
      JButton resetBtn = new JButton("Reset");
      resetBtn.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            vehicleField.setText("");
         }
      });
      JButton cancelBtn = new JButton("Cancel");
      cancelBtn.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            vehicleField.setText("");
            save = false;
            dispose();
         }
      });
      JPanel btnPanel = new JPanel(new GridLayout(1, 0, 4, 0));
      btnPanel.add(saveBtn);
      btnPanel.add(resetBtn);
      btnPanel.add(cancelBtn);

      int ebGap = 5;
      mainPanel.setBorder(BorderFactory.createEmptyBorder(ebGap, ebGap, ebGap,
               ebGap));
      mainPanel.setLayout(new BoxLayout(mainPanel, BoxLayout.PAGE_AXIS));
      mainPanel.add(textPanel);
      mainPanel.add(Box.createVerticalStrut(5));
      mainPanel.add(btnPanel);
   }

   private void dispose() {
      Window win = SwingUtilities.getWindowAncestor(mainPanel);
      win.dispose();
   }

   public String getVehicleText() {
      return vehicleField.getText();
   }

   public boolean isSave() {
      return save;
   }

   public JPanel getMainPanel() {
      return mainPanel;
   }

   @SuppressWarnings("serial")
   private class SaveAction extends AbstractAction {
      SaveAction() {
         super("Save");
      }

      public void actionPerformed(ActionEvent e) {
         save = true;
         dispose();
      }

   }
}

Best of luck, and hope this helps

edit: comments added to first class

[Mike Lipay]

Pete, thanks for all the work. It's taking me a while to go through and try to understand what all of it does. So much that is not covered in basic Java courses. Can you explain to me what this section is doing:

@SuppressWarnings("serial")  
    private class SaveAction extends AbstractAction {  
       SaveAction() {  
          super("Save");  
       }  

I read the AbstractAction on the Sun site, but the super("Save") just isn't making sense.

I can't find anything that explains the "@" statement, I know I use it in my existing code, but to be frank I lifted that from someone else's code on JavaRanch, with no understanding as to what "@" does. At first I thought is was a comment, but that doesn't seem to be the case.

Also, I understand your comments on using a layout manager, but I prefer to place the objects myself so that they blend in with the background images. Also, there is additional design (fields, etc.) that will be added, and the existing flow managers just aren't flexible enough to handle what I want to do.

This is a learning application, as well as my first attempt to create anything in Java. It was sparked by my current version of FileMaker not compatible with Apples next OS, and my lack of desire to spend a couple hundred to upgrade to the next version for three databases that I use locally. When I first purchased FM my needs were far more complex than they are now.

[pete stein]

Mike Lipay wrote:I read the AbstractAction on the Sun site, but the super("Save") just isn't making sense.

Have a look here: Swing Components Supporting Action. The super(String) calls the AbstractAction's constructor that uses a String parameter. It changes the text property of the button, setting the button's displayed text.

I can't find anything that explains the "@" statement, I know I use it in my existing code, but to be frank I lifted that from someone else's code on JavaRanch, with no understanding as to what "@" does. At first I thought is was a comment, but that doesn't seem to be the case.

@Xxxx declares an annotation. This one tells the compiler not to show a warning even though I did not give my AbstractAction a static long serialVersionUID field.

Also, I understand your comments on using a layout manager, but I prefer to place the objects myself so that they blend in with the background images. Also, there is additional design (fields, etc.) that will be added, and the existing flow managers just aren't flexible enough to handle what I want to do.

Check out all the layout managers and learn to use them nested and in concert with each other, because as your app gets more complex, trust me, your absolute positioning will become more and more of a chore and will hinder you.

This is a learning application, as well as my first attempt to create anything in Java. It was sparked by my current version of FileMaker not compatible with Apples next OS, and my lack of desire to spend a couple hundred to upgrade to the next version for three databases that I use locally. When I first purchased FM my needs were far more complex than they are now.

Best of luck with this!

[Mike Lipay]

Thanks for the descriptions, some are making sense. It's taking a while trying to figure out what in your version I need, versus what is just there because you didn't care for my coding.

I wish there was a "beginning" area for things like SWING. The beginning forum tells me to come here, here everyone assumes I am more advanced than I am. I find Sun's API a bit difficult to read, like diving into a chemical properties book before you're taken Chemistry 201.

[pete stein]

Mike Lipay wrote:I wish there was a "beginning" area for things like SWING. The beginning forum tells me to come here, here everyone assumes I am more advanced than I am. I find Sun's API a bit difficult to read, like diving into a chemical properties book before you're taken Chemistry 201.

But the more you "dive" the more familiar and comfortable you become with it. My suggestion: keep diving as much as you can.