当JComboBox中的itemStateChanged获得JTable的选定行

Question

I am trying to fetch the current row data while clicking on the combox. My problem is that if I try to fetch the details on clicking the combobox the data retrieved is wrong.

This is populating invalid data in the collection. Please follow exact steps mentioned below to replicate.

Please run the code to replicate the issue as it works only during initial selection but not after.

NOTE: Please CLICK DIRECLTY ONLY ON THE SECOND COLUMN

Step 1: Click on Second Column of Row 1
Step 2: Select- Item 1 
Step 3: Click on Second Column of Row 2
Step 4: Select- Item 2
Step 5: Click on Second Column of Row 3
Step 6: Select- Item 3
WORKS Fine till here :)
Step 7 : Click on Second column of Row 1 and do not change an selection leave it as it is (Just click on the combobox twice)
Step 8 : Click on Second column of Row 2, DO NO CHANGES
Step 9 : Click on Second column of Row 3, DO NO CHANGES
Step 10: NOW randomly click on any of the second columns of rows(1,2,3) and see the output datamap. It really wierd why the event is

Below is the sample code:

import java.awt.Cursor;
import java.awt.FlowLayout;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Vector;

import javax.swing.DefaultCellEditor;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JTable;
import javax.swing.JTextField;
import javax.swing.ListSelectionModel;
import javax.swing.SwingUtilities;
import javax.swing.table.DefaultTableModel;

public class TestJCombo extends JFrame {

    public TestJCombo() {
        initialize();
    }

    JTable jTable;
    JComboBox comboBox;
    Map<Integer, String> dataMap;

    private void initialize() {
        setSize(300, 300);
        setLayout(new FlowLayout(FlowLayout.LEFT));
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        final JTextField field = new JTextField();
        field.setSize(50000, 25);
        field.setText("                                                                                           ");

        jTable = new JTable();

        comboBox = new JComboBox();
        comboBox.setEditable(true);
        comboBox.addItem("item 1");
        comboBox.addItem("item 2");
        comboBox.addItem("item 3");
        comboBox.setEditable(false);

        dataMap = new LinkedHashMap();

        comboBox.addItemListener(new ItemListener() {

            public void itemStateChanged(ItemEvent e) {
                if (e.getStateChange() == ItemEvent.SELECTED) {

                    Object selected = comboBox.getSelectedItem();

                    int selectedRow = jTable.getSelectedRow();
                    selectedRow = jTable.convertRowIndexToModel(selectedRow);
                    if (selectedRow != -1) {
                        String user = (String) jTable.getValueAt(selectedRow, 0);
                        String data = "Row: " + (selectedRow + 1) + " :::: " + user + " , "
                                + comboBox.getSelectedItem();
                        dataMap.put(selectedRow + 1, "[" + user + " - " + comboBox.getSelectedItem() + "]");
                        if (selected != null) {
                            field.setText(data);
                        }
                        System.out.println("Current data map:: " + dataMap);
                    }
                }

            }
        });

        jTable.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        jTable.setRowHeight(30);
        jTable.setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR));

        DefaultTableModel myTableMdl = new DefaultTableModel();
        myTableMdl.addColumn("User");
        myTableMdl.addColumn("Role");
        jTable.setModel(myTableMdl);

        jTable.getColumn("Role").setCellEditor(new DefaultCellEditor(comboBox));

        Vector tableData;
        for (int i = 1; i <= 7; i++) {
            tableData = new Vector();
            tableData.add("User " + i);
            myTableMdl.addRow(tableData);
        }

        getContentPane().add(jTable);
        getContentPane().add(field);

    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new TestJCombo().setVisible(true);
            }
        });
    }
}

Answer 1

The problem is that you are using the wrong listener on the wrong component. You should not be adding a listener to the combo box. The point of using an editor is to edit the data and update the TableModel . You should not be referencing the combo box for further processing.

So instead you should be adding a TableModelListener to the TableModel . Then a TableModelEvent will be generated whenever the value in column 2 is changed. The TableModelEvent will contain the row/column information of the cell that was changed.

You can check out: JTable -> TableModeListener for a basic example of using a TableModelListener. In your case you check if the second column changed and then you update your map.

Also note you are using the convertRowIndexToModel() method incorrectly:

selectedRow = jTable.convertRowIndexToModel(selectedRow);
...
    String user = (String) jTable.getValueAt(selectedRow, 0);

First of all you only need to worry about coverting the row index if the table view is sorted or filtered. In the code provided you don't do either so there is no need to convert the index.

However, if you ever did sort of filter the view then you would need convert the view row to the model row and then you must access the data from the model, not the view. So the code would be:

String user = (String) jTable.getModel().getValueAt(selectedRow, 0);

Answer 2

The problem is that you are creating one JComboBox and then putting it on all the cells in the column. You are referencing the JComboBox , not creating a new one for each cell. This is why when you follow the 10 steps you mentioned, the result is obtained is wildly foolish and senseless.

Here is the fix, create a custom TableCellEditor for all the cells that are in column 1 (Role column). The goal is to create a brand new JComboBox for each cell. This is achieved by changing the declaration of the JTable to jtable = new JTable(){...}; to override the getCellEditor(...){...} method. Also, the method private JComboBox createComboBox() {...} is what you need for brand new JComboBox creation.

Now, we will take out the addItemListener and replace it with addActionListener . This is needed because the itemStateChanged in ItemListener will be not invoked if the user selects the item that is already selected. We need to somewhat replicate a two-mouse-click, one for showing the dropdown list and the second for selecting the item (you can skip this step if not needed).

I have also edited your code to make it more readable and efficient .

Here is an MVCE:

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

import javax.swing.table.TableCellEditor;

import java.awt.Cursor;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Vector;
import javax.swing.Box;
import javax.swing.BoxLayout;

import javax.swing.DefaultCellEditor;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTable;
import javax.swing.JTextField;
import javax.swing.ListSelectionModel;
import javax.swing.SwingUtilities;
import javax.swing.table.DefaultTableModel;

public class TestJCombo extends JFrame {

    JTable jTable;
    //JComboBox comboBox;//not needed, replaced by the createComboBox() method.
    Map<Integer, String> dataMap;
    final JTextField FIELD = new JTextField(25);//must put this globally.
    //Since it is final, it should be all in upper case

    //It is a good practice to put the global variables on top and constructor(s) below.
    public TestJCombo() {
        initialize();
    }

    private void initialize() {
        //use pack(); instead setSize(...); I used it at the end of this method.
        //setSize(300, 300);
        setLayout(new FlowLayout(FlowLayout.LEFT));
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setLocationRelativeTo(null);
        //both lines not needed, it has been taken care of when FIELD was declared.
        //FIELD.setSize(50000, 25);
        //FIELD.setText("                                         "
        //  + "                                                  ");

        //Must create a seperate TableCellEditor for each cell in the table.
        jTable = new JTable() {
            public TableCellEditor getCellEditor(int row, int column) {
                int modelColumn = convertColumnIndexToModel(column);
                //if the cell lies in the second column, create a custom cell editor.
                if (modelColumn == 1) {
                    return (TableCellEditor) new DefaultCellEditor(createComboBox());
                } else {
                    return super.getCellEditor(row, column);
                }
            }
        };

        //comboBox = new JComboBox();
        //comboBox.setEditable(true);
        //comboBox.addItem("item 1");
        //comboBox.addItem("item 2");
        //comboBox.addItem("item 3");
        //comboBox.setEditable(false);
        dataMap = new LinkedHashMap();

        jTable.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        jTable.setRowHeight(30);
        jTable.setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR));

        DefaultTableModel myTableMdl = new DefaultTableModel();
        myTableMdl.addColumn("User");
        myTableMdl.addColumn("Role");
        jTable.setModel(myTableMdl);

        //we have our own custom CellEditor, this is not needed
        //jTable.getColumn("Role").setCellEditor(new DefaultCellEditor(comboBox));
        Vector tableData;
        for (int i = 1; i <= 7; i++) {
            tableData = new Vector();
            tableData.add("User " + i);
            myTableMdl.addRow(tableData);
        }

        //It is better practice to add everything to a 
        //panel and then add that panel to the frame.
        JPanel panel = new JPanel();
        panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));

        panel.add(jTable);
        panel.add(Box.createRigidArea(new Dimension(0, 10)));//add some space
        panel.add(FIELD);
        getContentPane().add(panel, BorderLayout.CENTER);
        pack();//should use this.
    }

    private JComboBox createComboBox() {
        JComboBox comboBox = new JComboBox();
        comboBox.setEditable(true);
        comboBox.addItem("item 1");
        comboBox.addItem("item 2");
        comboBox.addItem("item 3");
        comboBox.setEditable(false);

        //Add an ActionListener so that it would also detect if the user selects
        //the same item. The itemStateChanged in the ItemListener will not be
        //invoked if the user selects the item that is already selected.
        comboBox.addActionListener(new ActionListener() {
            //To update the result everytime the user selects an item
            //(regardless if it was selected or not), we need to "mock"
            //a two-click operation. The first click will show the 
            //drop-down list to select from and the second will
            //allow the user to select the desired choice to be selected.
            boolean doubleClick = false;

            @Override
            public void actionPerformed(ActionEvent ae) {
                if (doubleClick) {
                    int selectedRow = jTable.getSelectedRow();
                    selectedRow = jTable.convertRowIndexToModel(selectedRow);
                    Object selected = comboBox.getSelectedItem();
                    if (selectedRow != -1 && selected != null) {
                        String user = (String) jTable.getValueAt(selectedRow, 0);
                        String data = "Row: " + (selectedRow + 1) + " :::: " + user + " , "
                            + comboBox.getSelectedItem();
                        dataMap.put(selectedRow + 1, "[" + user + " - "
                            + comboBox.getSelectedItem() + "]");
                        FIELD.setText(data);
                        System.out.println("Current data map:: " + dataMap);
                    }
                    doubleClick = false;
                }
                doubleClick = true;
            }
        });

//      comboBox.addItemListener(new ItemListener() {
//
//          public void itemStateChanged(ItemEvent e) {
//              if (e.getStateChange() == ItemEvent.SELECTED) {
//
//                  Object selected = comboBox.getSelectedItem();
//
//                  int selectedRow = jTable.getSelectedRow();
//                  selectedRow = jTable.convertRowIndexToModel(selectedRow);
//                  if (selectedRow != -1) {
//                      String user = (String) jTable.getValueAt(selectedRow, 0);
//                      String data = "Row: " + (selectedRow + 1) + " :::: " + user + " , "
//                          + comboBox.getSelectedItem();
//                      dataMap.put(selectedRow + 1, "[" + user + " - "
//                      + comboBox.getSelectedItem() + "]");
//                      if (selected != null) {
//                          FIELD.setText(data);
//                      }
//                      System.out.println("Current data map:: " + dataMap);
//                  }
//              }
//
//          }
//      });
        return comboBox;
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new TestJCombo().setVisible(true);
            }
        });
    }
}