JTabbedPane - Previously selected Tab.

[Rob Elliott]

Hi All,
I'm using a JTabbedPane and want to do some field validation at the moment the user selects another Tab. Potentially, depending on their reply to a messagebox, keep them on the same tab to correct bad data.
I'm implementing the ChangeListener interface and handling stateChanged events however getSelectedIndex() returns the newly selected tab.
Is there easy way to
1) Determine which was the previously selected Tab and
2) Prevent the user from going to the newly selected Tab in the case of data validation failure? A stateChanged event cannot be consumed.
Thanks in advance,
Rob.

[Nathan Pruett]

"RE" -

Welcome to the JavaRanch! Please adjust your displayed name to meet the
JavaRanch Naming Policy.
You can change it here.

Here's a small example that should help you... you'll have to save the current index and compare it in the ChangeListener...

import javax.swing.*;
import javax.swing.event.ChangeListener;
import javax.swing.event.ChangeEvent;
 
public class TabTest extends JFrame implements ChangeListener{
 
    private JTabbedPane tabs;
    private int selectedIndex;
    private JCheckBox[] valid;
 
    public TabTest() {
        super( "TabTest" );
        tabs = new JTabbedPane();
        valid = new JCheckBox[ 3 ];
        JPanel one = new JPanel();
        one.add( new JLabel( "First Tab" ) );
        valid[0] = new JCheckBox( "Valid" );
        one.add( valid[0] );
        tabs.addTab( "One", one );
        JPanel two = new JPanel();
        two.add( new JLabel( "Second Tab" ) );
        valid[1] = new JCheckBox( "Valid" );
        two.add( valid[1] );
        tabs.addTab( "Two", two );
        JPanel three = new JPanel();
        three.add( new JLabel( "Third Tab" ) );
        valid[2] = new JCheckBox( "Valid" );
        three.add( valid[2] );
        tabs.addTab( "Three", three );
        selectedIndex = tabs.getSelectedIndex();
        tabs.addChangeListener( this );
        getContentPane().add( tabs );
    }
 
    public void stateChanged( ChangeEvent e ) {
        if ( tabs.getSelectedIndex() != selectedIndex ) {
            if ( valid[selectedIndex].isSelected() ) {
                selectedIndex = tabs.getSelectedIndex();
            }
            else {
                tabs.setSelectedIndex( selectedIndex );
            }
        }
    }
 
    public static void main( String[] args ) {
        JFrame f = new TabTest();
        f.setDefaultCloseOperation( WindowConstants.EXIT_ON_CLOSE );
        f.setSize( 300, 300 );
        f.show();
    }
}

Thanks! and welcome to the JavaRanch!

[Paulo Guzman]

You can extends JTabbedPane to override the setSelectedIndex method and then call super.setSelectedIndex(index); after doing your validation something like:

public class ValidationTabbedPane extends JTabbedPane {
    private static final long serialVersionUID = 1L;

    public ValidationTabbedPane() {
        super();
      }

      @Override
      public void setSelectedIndex(int index) {
          if (index >= 0 && index < getTabCount()) {
              if(getSelectedIndex() == -1) {
                  super.setSelectedIndex(index);
              } else  {
                  Containers tab = tabs.get(getSelectedIndex());
                  boolean change = true;
                  if(tab.isDirty()) {
                      if(!MessageAlert.
                              yesNoMessage("You have unsaved changes. Do you want to change tab anyways? ", 
                                      mainTabbedPane)) {
                          change = false;
                      }
                  }
                  if(change) {
                      super.setSelectedIndex(index);
                  }
              }
          }           
      }
}