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Swing / AWT / SWT

Array of JButtons

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posted 20 years ago

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Hi Fellas..
I'm having lots of problems with my array of jbuttons... i dont know how to do the button's addActionListener... here's how my code looks like:

dates = new Vector();
subjects = new Vector();
messages = new Vector();

dates.add("01/01/2001");
dates.add("02/02/2001");
dates.add("03/03/2001");
dates.add("04/04/2001");
dates.add("05/05/2001");

subjects.add("<html>Just in case [ Message ID: 1 ]</html>");
subjects.add("<html>Nothing real [ Message ID: 2 ]</html>");
subjects.add("<html>Oh yeah yeah [ Message ID: 3 ]</html>");
subjects.add("<html>My Shiznesss [ Message ID: 4 ]</html>");
subjects.add("<html>Why do you hack [ Message ID: 5 ]</html>");

messages.add("First Message");
messages.add("Second Message");
messages.add("Third Message");
messages.add("Fourth Message");
messages.add("Fifth Message");

row = 6;
for(i=0; i<numMsgs; i++) {
row++;
label_date[i] = new JLabel("" + dates.get(i) + "");
label_date[i].setFont(new Font("Helvetica", Font.PLAIN, 12));
gbc.fill = GridBagConstraints.NONE;
gbc.anchor = GridBagConstraints.SOUTHWEST;
gbc.ipadx = 0;
//gbc.ipady = -5;
gbc.gridy = row; // row
gbc.gridx = 1; // column
gbc.insets = new Insets(0,20,5,0); // top, left, bottom, right
gridbag.setConstraints(label_date[i], gbc);
panel.add(label_date[i]);
label_date[i].setForeground(new Color(0x000000));

button_subject[i] = new JButton("" + subjects.get(i) + "");
button_subject[i].setFont(new Font("Helvetica", Font.PLAIN, 12));
gbc.anchor = GridBagConstraints.NORTHWEST;
gbc.fill = GridBagConstraints.NONE;
gbc.ipadx = 0;
gbc.ipady = 0;
gbc.gridy = row; // row
gbc.gridx = 1; // column
gbc.insets = new Insets(0,100,5,0); // top, left, bottom, right
gridbag.setConstraints(button_subject[i], gbc);
panel.add(button_subject[i]);
button_subject[i].setForeground(new Color(0x000000));
button_subject[i].setBackground(new Color(0xeaeaea));
button_subject[i].setBorder(BorderFactory.createEmptyBorder());

button_subject[i].addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent evt) {
System.out.println("" + messages.get(i));
// pop up a screen on the message..
// MessageDisplayer.displayMessage(evt);
}
});

}

So now, when i click on the buttons... it gives me a null pointer exception.. i know why that happens: it's because i=5.. right? but i have no idea how to associate message.get(4) with button[4]... or message.get(2) with button[2]... and i dont want to hardcode all this in cuz the values are gonna be dynamic..
any way i can get around this prob? your help is very much appreciated..
thank you.
rocky

Craig Wood

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Posts: 1535

posted 20 years ago

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You generally have two options:
1 - name each button and put the names in the button_subject array; here you can test for each button in actionPerformed with if(button == namedButton),
2 - set an action command for each button in the array as shown below; here you can test for the button with if(ac.equals("id1")).
One benefit of the second approach is that your code will not break when internationalized, the text on the button will be changed but the action command string will be unchanged.

You could of course add an individual ActionListener to each button as you were doing, there's nothing wrong with doing it that way.

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
 
public class DesignTest
{
 public static void main(String[] args)
 {
 Vector
 dates = new Vector(),
 subjects = new Vector(),
 messages = new Vector();
 
 dates.add("01/01/2001");
 dates.add("02/02/2001");
 dates.add("03/03/2001");
 dates.add("04/04/2001");
 dates.add("05/05/2001");
 
 subjects.add("<html>Just in case [ Message ID: 1 ]</html>");
 subjects.add("<html>Nothing real [ Message ID: 2 ]</html>");
 subjects.add("<html>Oh yeah yeah [ Message ID: 3 ]</html>");
 subjects.add("<html>My Shiznesss [ Message ID: 4 ]</html>");
 subjects.add("<html>Why do you hack [ Message ID: 5 ]</html>");
 
 messages.add("First Message");
 messages.add("Second Message");
 messages.add("Third Message");
 messages.add("Fourth Message");
 messages.add("Fifth Message");
 
 String[] actionCommands = { // alternative to vectors
 "id1", "id2", "id3", "id4", "id5"
 };
 
 JLabel[] label_date = new JLabel[5];
 JButton[] button_subject = new JButton[5];
 
 Font font = new Font("Helvetica", Font.PLAIN, 12); // factor out
 Color // elements used
 textColor = new Color(0x000000), // multiple times,
 backgroundColor = new Color(0xeaeaea); // requires fewer
 ActionListener listener = new ActionListener() // new objects
 {
 public void actionPerformed(ActionEvent e)
 {
 JButton button = (JButton)e.getSource();
 String ac = button.getActionCommand();
 System.out.println("ac = " + ac);
 }
 };
 GridBagLayout gridbag = new GridBagLayout();
 JPanel panel = new JPanel(gridbag);
 GridBagConstraints gbc = new GridBagConstraints();
 gbc.fill = GridBagConstraints.NONE; // factor out common
 gbc.ipadx = 0; // constraints
 gbc.gridx = 1;
 gbc.gridy = 1;
 
 for(int i = 0; i < dates.size(); i++)
 {
 label_date[i] = new JLabel("" + dates.get(i) + "");
 label_date[i].setFont(font);
 gbc.anchor = GridBagConstraints.SOUTHWEST;
 //gbc.ipady = -5;
 gbc.gridy++; // row
 gbc.insets = new Insets(0,20,5,0); // top, left, bottom, right
 gridbag.setConstraints(label_date[i], gbc);
 panel.add(label_date[i]);
 label_date[i].setForeground(textColor);
 
 button_subject[i] = new JButton("" + subjects.get(i) + "");
 button_subject[i].setFont(font);
 gbc.anchor = GridBagConstraints.NORTHWEST;
 gbc.ipady = 0;
 gbc.insets = new Insets(0,100,5,0); // top, left, bottom, right
 gridbag.setConstraints(button_subject[i], gbc);
 panel.add(button_subject[i]);
 button_subject[i].setForeground(textColor);
 button_subject[i].setBackground(backgroundColor);
 button_subject[i].setBorder(BorderFactory.createEmptyBorder());
 button_subject[i].setActionCommand(actionCommands[i]);
 button_subject[i].addActionListener(listener);
 }
 
 JFrame f = new JFrame();
 f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 f.getContentPane().add(panel);
 f.setSize(400,300);
 f.setLocation(200,200);
 f.setVisible(true);
 }
}

Rocky Summers

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Posts: 66

posted 20 years ago

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hi craig!
thanks for the answer! i tried doing the exact same thing.. but one thing bothers me though.. what if one of the names of the buttons have the exact same text.. cuz what i'm doing here, is i'm grabbing stuff from the database and putting them in buttons so when i click on that button, i can open up a small popup on that field's corresponding info..

Craig Wood

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posted 20 years ago

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Then adding an action listener to each button makes more sense.

Nathan Pruett

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posted 20 years ago

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The above option is probably the best for this case, but I would also like to point out that you could still do the one big listener option even if buttons had the same text. The actionCommand of the button is by default the same as the text, but you can set it to anything you want. This is the value you can use in your listener to differentiate between multiple buttons with the same displayed text.

-Nate
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