Button ActionListener not called inside class extending JPanel

Question

I have a main frame, called FrontGUI, with a side panel added to it. This side panel is a class called FrontGUILinker that extends JPanel, and has a button on it. When I run the program, the button doesn't do anything - the ActionListener doesn't ever seem to be called. I have several other components with similar setups, and the buttons all work on them - the only difference I can see is that they are extensions of JFrame, and they aren't direct fields of FrontGUI but instead of the maingui mentioned in the code below. This maingui contains fields with Controller classes for each frame, including FrontGUIController, but the FrontGUILinkerController is a field in FrontGUIController. Here are outlines of my classes, with hopefully just the unrelated things left out. The main JFrame class:

public class FrontGUI extends JFrame {
    public FrontGUILinker linkerPanel;
    public JButton btnShowhideLinker;

    public FrontGUI() {
      linkerPanel = new FrontGUILinker();
      contentPane.add(linkerPanel, BorderLayout.EAST);

      btnShowhideLinker = new JButton("Show/Hide Linker");
      contentPane.add(btnShowhideLinker);
    }
}

Here's it's "controller" class. The side panel can be shown or not shown, which is what this action listener does, and this seems to work just fine.

public class FrontGUIController {
    public MAINGUI maingui;
    private FrontGUI frame;
    public FrontGUILinkerController linkerController;

    public FrontGUIController(MAINGUI parent) {
       maingui = parent;
       frame = new FrontGUI();
       linkerController = new FrontGUILinkerController(maingui);

       //Button: Show/Hide linkerPanel
       frame.btnShowhideLinker.addActionListener( new ActionListener() {
       @Override
       public void actionPerformed(ActionEvent arg0) {
           frame.linkerPanel.setVisible(!frame.linkerPanel.isVisible());
       }});

    }

}

Here is the FrontGUILinker class:

public class FrontGUILinker extends JPanel {
   public btnCreateLink;

   public FrontGUILinker() {
       btnCreateLink = new JButton("Create Link");
       add(btnCreateLink);
   }
}

Here is the controller for that class:

public class FrontGUILinkerController {
   public MAINGUI maingui;
   private FrontGUILinker frame;

   public FrontGUILinkerController(MAINGUI parent) {
      maingui = parent;
      frame = new FrontGUILinker();

      // Add listener to Create Link button
      frame.btnCreateLink.addActionListener( new ActionListener() {
         @Override
         public void actionPerformed(ActionEvent arg0) {
             System.out.println("Create Link button has been clicked");
         }});
   }
}

Anybody have an idea why this isn't working?

Have you tried a println in the show/hide button action listener, to see if it's actually being called? I've often found in Swing that update requests don't always "work" until you do a combination of validate/revalidate/repaint. See http://stackoverflow.com/questions/1097366/java-swing-revalidate-vs-repaint — Ash, Nov 24 '12 at 01:00
Your code doesn't make sense. You have two classes named FrontGUILinker? I think you're showing the wrong class name for the bottom controller class -- a nasty typo. Please correct this. — Hovercraft Full Of Eels, Nov 24 '12 at 01:09
1) Don't extend `JFrame`, just use an instance of one. 2) (Probably) don't extend `JPanel` either (ditto). 3) For better help sooner, post an [SSCCE](http://sscce.org/). 4) Please learn common [Java naming conventions](http://java.sun.com/docs/books/jls/second_edition/html/names.doc.html#73307) (specifically the case used for the names) for class, method & attribute names & use it consistently. — Andrew Thompson, Nov 24 '12 at 01:12
@HovercraftFullOfEels Sorry, fixed it now. The bottom controller class is FrontGUILinkerController. — FrancesKR, Nov 24 '12 at 20:37
@AndrewThompson 1 and 2) We've been extending JFrame to avoid making our classes too huge. It seems like if we just use instances of JFrame and JPanel, we'll have to put all our code for their various buttons, text boxes, etc, in the one class that we've created the instances in. Is there a better way to do this without extending JFrame and JPanel? 3) I'll check that out! 4) This is from an existing project that I didn't start myself, but I'll keep that in mind. — FrancesKR, Nov 24 '12 at 20:40

Hovercraft Full Of Eels · Accepted Answer · 2012-11-24T01:55:05.643

You're creating FrontGUILinker instances twice, one you're displaying and one you're adding an ActionListener to. Don't do that. Create this object once and use the same reference for both. To show that I'm right, just look at the code in your question above, and search out where you call new FrontGUILinker() and you'll see that you do it twice, here:

public FrontGUI() {
  linkerPanel = new FrontGUILinker();

and again here:

public FrontGUILinkerController(MAINGUI parent) {
  maingui = parent;
  frame = new FrontGUILinker();

Each instance is completely distinct from the other, and so adding an ActionListener to one will have no effect on the other one (the displayed one). To solve this, pass valid references to where they're needed.

i.e.,

public class FrontGUILinkerController {
   public MAINGUI maingui;
   private FrontGUILinker frame;

   // **** note change
   public FrontGUILinkerController(MAINGUI parent, FrontGUILiner frame) {
      maingui = parent;
      this.frame = frame;  // **** added
      // frame = new FrontGUILinker(); // **** commented out

      // Add listener to Create Link button
      frame.btnCreateLink.addActionListener( new ActionListener() {
         @Override
         public void actionPerformed(ActionEvent arg0) {
             System.out.println("Create Link button has been clicked");
         }});
   }
}

and

public FrontGUIController(MAINGUI parent) {
   maingui = parent;
   frame = new FrontGUI();
   linkerController = new FrontGUILinkerController(maingui, frame); // **** changed

I got this to work, but in the FrontGUIController class I instead wrote: `linkerController = new FrontGUILinkerController(maingui, frame.linkerPanel);` and in FrontGUILinkerController I had to delete the whole `private FrontGUILinker frame` line and add `final` to the frame parameter to the constructor. I'm not entirely sure why these changes were necessary, so any explanation would be welcome, but it's working as expected now! Thank you! — FrancesKR, Nov 28 '12 at 23:30
Actually, I can keep the `private FrontGUILinker frame` line so that I can use it in other methods in FrontGUILinkerController. It just gave me a warning that it wasn't used because I had only used the frame that was passed as a parameter to FrontGUILinkerController(). — FrancesKR, Nov 29 '12 at 01:27

Button ActionListener not called inside class extending JPanel

1 Answers1