CODEWITHSUNDEEP
javajcombobox
user3245747
user3245747

Reputation: 937

The text in the JComboBox displays a string but the selection is actually set to null

I have a JComboBox which I create with the following code:

employeeDeletetxt = new JComboBox(buildComboBoxmodel("SELECT employee_id, employee_first_name     FROM employees"));
employeeDeletetxt.setSelectedItem(null);

Now, when I run the program the selection is set to null so nothing is displayed in the combo box. I have an ActionListener for a delete button. The ActionListener would delete certain records and when this happens I need the data in the JComboBox to reflect the recent changes. I use the following code:

employeeDeletetxt.removeItem(employeeDeletetxt.getSelectedItem());                      
employeeDeletetxt.setSelectedItem(null);

The problem is that the text displayed in the JComboBox is not empty after these lines are called. However, the item which the JComboBox points to is actually null because I get the following error message when I call the ActionListener directly after I have called it the previous time:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

How can I set the text to be empty?

Upvotes: 2

Views: 1427

Answers (3)

user3245747
user3245747

Reputation: 937

I found the solution to the problem and would like to share it with everyone in case someone else has the same problem. As I stated above, the AutoCompleteDecorator was what was causing the problem in the first place. If I removed it then the program would work as expected. However I wanted to provide the user with the ability to search. The solution is to use AutoCompletion instead which is found in the following link: http://www.orbital-computer.de/JComboBox/source/AutoCompletion.java. now, in the program, instead of using: AutoCompleteDecorator.decorate(employeeDeletetxt); I use: AutoCompletion.enable(employeeDeletetxt); This way I allow the user to use the autocomplete option while also being able to set the current selection of the combo box to null.

Upvotes: 2

ROT13
ROT13

Reputation: 375

I tried to implement what you described and got to this:

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;


public class TestGui extends JFrame{

JPanel contentPane = new JPanel();
JButton button = new JButton("Press me!");
JComboBox comboBox = new JComboBox(new String[] {"None", "Help"});


public TestGui() {

    initalise();
}

private void initalise() {

    this.setDefaultCloseOperation(EXIT_ON_CLOSE);

    this.comboBox.setSelectedItem(null);    
    this.contentPane.setLayout(new GridLayout(2,1));
    this.contentPane.add(comboBox);
    this.contentPane.add(button);

    this.button.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent arg0) {
            comboBox.removeItem(comboBox.getSelectedItem());
            comboBox.setSelectedItem(null);

        }
    });

    this.setContentPane(this.contentPane);

    this.pack();
    this.setVisible(true);
}

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

        @Override
        public void run() {

            new TestGui();
        }
    });
}

}

My program runs exactly the way you described. Maybe you can find your problem.

Upvotes: 1

John Dorlus
John Dorlus

Reputation: 59

The problem is that you are setting the current item to null which is different than setting it to an empty string. You can do something like:

employeeDeletetxt.setSelectedItem("").

What I would probably do is create a method that has a loop that creates an array of strings for your combobox and always have the first element be the empty string. That way, once the array is built, you add the rest of your elements retrieved from your query. If your query returns no results, you will just have the text box with the one blank element.

Upvotes: -1

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