如何在jSwing组合框中到达对象？

Question

I'm working on a maven based java desktop application and I'm using jSwing frames for interface. I need to show people Tasks with their names at combobox, but I'm not sure about I did it well.

In this code section, I got Tasks from my database as Lists, then I showed them at combobox.

List<TmsTask> task;
    int i;
    try {
        task = Application.getApp().getMainService().getTasksList();
        for (i = 0; i <= task.size(); i++) {
            jComboBoxTask.setModel(new javax.swing.DefaultComboBoxModel<>(new String[]{task.get(i).getTaskName(), 
                                                                                       task.get(i + 1).getTaskName(),
                                                                                       task.get(i + 2).getTaskName()}));
        }

    } catch (Exception ex) {
        Logger.getLogger(BindTask.class.getName()).log(Level.SEVERE, null, ex);
    }

It's oke , I can see Task names at combobox.

The problem is; I want to save an other info to database using that task. But as you see, selected things(at combobox) just task names, not task objects.

How can I put task objects at combobox option sections?

In this code section, I used to try taking Task objects from database and showing them at combobox sections, but combobox sections all shows same taskname.

private void jComboBoxTaskMousePressed(java.awt.event.MouseEvent evt) {                                           
    TmsTask task;

    try {
        task = Application.getApp().getMainService().getTasks();

            jComboBoxTask.setModel(new javax.swing.DefaultComboBoxModel<>(new String[]{task.getTaskName(), 
                                                                                       task.getTaskName(),
                                                                                       task.getTaskName()}));


    } catch (Exception ex) {
        Logger.getLogger(BindTask.class.getName()).log(Level.SEVERE, null, ex);
    }

}

Thanks for your help, best regards.

Answer 1

for (i = 0; i <= task.size(); i++) 
{
    jComboBoxTask.setModel(new javax.swing.DefaultComboBoxModel<>(
       new String[]{task.get(i).getTaskName(), task.get(i + 1).getTaskName(),

You can't keep creating a new model. This means only the last task will ever be displayed.

You need to:

1. set the model outside the loop
2. use the addItem(...) method of the combo box to add each item.

Although I question if you should even be using a combo box.

I would suggest a JTable , which displays the data in row and columns would be better. Read the section from the Swing tutorial on How to Use Tables for more information.

Edit:

You can store any object in a combo box. The default renderer simply uses the toString() method of the object to display the value in the combo box.

So you can add a Task object to the combo box and then you will need to create a custom renderer to display the "task name" in the combo box. See Combobox With Custom Renderer for more information on this topic and a simple example of a renderer.

Answer 2

@camickr is right (in comments). Using a combo box to show all fields from an Object doesn't make much sense. Just override the toString method from your object and the default renderer will show it.

Here is how you do it with a simple Person object (name,age).

package test;

import java.awt.Dimension;
import java.awt.FlowLayout;

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

public class ObjectsInComboBox extends JFrame {
    public ObjectsInComboBox() {
        super("combo boxes");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setPreferredSize(new Dimension(300, 300));
        getContentPane().setLayout(new FlowLayout());

        JComboBox<Person> personComboBox = new JComboBox<>();
        getContentPane().add(personComboBox);
        pack();
        personComboBox.addItem(new Person("John", 31));
        personComboBox.addItem(new Person("George", 55));
        personComboBox.addItem(new Person("Mike", 12));
        personComboBox.addItem(new Person("Brian", 36));
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            ObjectsInComboBox frame = new ObjectsInComboBox();
            frame.setVisible(true);
        });
    }
}

class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return name + " - " + age; //toString override so renderer can show it.
    }
}