Disable Open button in JFileChooser?

Question

I extended a JFileChooser and overrode the approveSelection method so that when a user chooses an invalid directory and then clicks on the Open button, an error message in a JOptionPane will be displayed. But I want to make my JFileChooser more user-friendly and make the Open button become disabled when a user clicks on an invalid directory and then become re-enabled when a user clicks on a valid directory. Is it possible to customize my JFileChooser even further and get access to the Open button so that I can change the status of the button accordingly (possibly via a listener that listens for a directory selection)?

public class MyFileChooser extends JFileChooser {

  private final JFrame mainFrame;

  public MyFileChooser(JFrame mainFrame) {
    this.mainFrame = mainFrame;
    setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
  }

  @Override
  public void approveSelection() {
    if (/* directory is valid */) {
      super.approveSelection();
      return;
    }
    JOptionPane.showMessageDialog(mainFrame, "Invalid directory", "Error", JOptionPane.ERROR_MESSAGE);
  }

}

Answer 1

you can hide the accept/cancel buttons by calling chooser.setControlButtonsAreShown(false) when detect any selecting change on files/directories:

myChooser.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);
myChooser.addPropertyChangeListener(new PropertyChangeListener() {
  public void propertyChange(PropertyChangeEvent evt) {
        if (JFileChooser.SELECTED_FILE_CHANGED_PROPERTY.equals(evt.getPropertyName())) {
            File file = (File) evt.getNewValue();
            if (file != null && file.isFile()) {    // your condition                  
                myChooser.setControlButtonsAreShown(false);
            }
            else if ( file != null ) {
                System.out.println(file.getName());
                myChooser.setControlButtonsAreShown(true);
            }
        }

        myChooser.repaint();
    }
});

but it may confuse the user, its better to make custom FileFilter and showing only the files/directories you need:

public static class MyDirectoryFilter extends javax.swing.filechooser.FileFilter {
  @Override
  public boolean accept( File file ) {
    return file.isDirectory() && customeCondition(file) ;
  }

  @Override
  public String getDescription() {
    return "this only my custom dir";
  }
}

myChooser.setFileFilter( new MyDirectoryFilter () );

Edit: I found a way to disable the button, by iterating over the components and getting handle to Open button : http://www.coderanch.com/t/468663/GUI/java/Disabling-Enabling-level-button-folder

example:

myChooser.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);
myChooser.addPropertyChangeListener(new PropertyChangeListener() {
public void propertyChange(PropertyChangeEvent evt) {
    if (JFileChooser.SELECTED_FILE_CHANGED_PROPERTY.equals(evt.getPropertyName())) {
           File file = (File) evt.getNewValue();

           if (file != null && file.isFile()) { 
                setOpenButtonState(myChooser, false);

           }
           else if ( file != null ) {
                setOpenButtonState(myChooser, true);
                System.out.println(file.getName());
           }
        }

        myChooser.repaint();
    }
});

public static void setOpenButtonState(Container c, boolean flag) {
    int len = c.getComponentCount();
    for (int i = 0; i < len; i++) {
      Component comp = c.getComponent(i);

      if (comp instanceof JButton) {
        JButton b = (JButton) comp;

        if ( "Open".equals(b.getText()) ) {
            b.setEnabled(flag);
        }

      } else if (comp instanceof Container) {
          setOpenButtonState((Container) comp, flag);
      }
    }     
}