Java JTable TableModel addRow不变

Question

I have more of a problem than a question and hope you can help me find possible reasons for this.

In a very simple JTable , where I use the DefaultTableModel . I add a row programmatically during the runtime like this:

public void Update(String neu) {
    System.out.println(model.getDataVector());

    model.addRow(new String[] {neu});

    System.out.println(model.getDataVector());
}

The System-Prints are only a debugging measure for me to realize more. Whenever this method runs, I actually add something to the TableModel (prove due to the out.prints)

But the change is not permanent. Neither do I see a change in my table, nor is the "new value" part of the TableModel the next time the method Update is called.

What could be the reason?

Edit1: Sadly I cannot make a code snippet small enough to be posted here and yet contain the error. I would highly appreciate it however if you guys could give me some hints in generall what might cause the abovementioned behaviour.

EDIT2: I have build a workaround in my code. Somehow the problem seemed to be caused by using two different frames for this operation (one frame to ask for the value and the second frame to use and display this value)

I replaced one frame with a JDialog and now the TableModel updates correctly. I do not know what the problem with using two frames was, but at least I have my code working again. Thank you for your help!

Answer 1

When you change data in tableModel, table is not repainted. Try to call model.fireTableDataChanged(); after adding new row to table model.

EDIT: fireTableDataChanged will not solve your problem, because it is called automatically as mentioned in comment below.

Another problem I see is that you have two different fields/data models - mdlUebersetzung and model . One that you use for loggin, one for addingRow. Is it same instance of TableModel?

Answer 2

I tried to write this simple example using exactly your method and it looks like it works.

Here's my code:

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

public class MyTable extends JFrame implements ActionListener {

    private JTable table;
    private DefaultTableModel model;

    private JButton addButton; // by clicking the button a new row will be added to the table

    // just create the table and set up the interface
    public MyTable() {
        table = new JTable(0,1); // this creates a new Table with 0 rows and 1 column having a DefaultTableModel
        model = (DefaultTableModel) table.getModel();

        JScrollPane tablePanel = new JScrollPane(table);

        addButton = new JButton("Add row");
        addButton.addActionListener(this);
        JPanel buttonPanel = new JPanel();
        buttonPanel.add(addButton);

        setLayout(new BorderLayout());
        add(tablePanel);
        add(buttonPanel, BorderLayout.PAGE_END);

        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        pack();
        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        if(e.getSource() == addButton) {
            Update("new Row text");
        }
    }

    public void Update(String neu) {
        System.out.println(model.getDataVector());

        model.addRow(new String[] {neu});

        System.out.println(model.getDataVector());
    }

    public static void main(String[] args){
        new MyTable();
    }
}

The thing I noticed is that if I create the JTable using the constructor with no arguments, ie new JTable() , the rows added to the model are all empty (which can be noticed looking at the prints in the terminal), even if I'm passing new String[] {neu} as argument. This is weird because according to the documentation that constructor should return a JTable having a "default data model", which I guess is obtained by calling the createDefaultDataModel() method of JTable, whose documentation says in turn that by default it returns a DefaultTableModel .

EDIT: I noticed now that the constructor for DefaultTableModel with no arguments builds a table model with "zero columns and zero rows".

As noted by peeskillet in a comment, always remember to add the action listener to the buttons to actually make them do something!