Listen for an events for Swing objects in a separate class?

Question

Hi all, sorry if this is in the wrong section of the forum but since this is a problem I am having with a Swing based project I thought i'd come here for help. Essentially i have nested panels in separate classes for the sake of clarity and to follow the ideas of OO based development. I have JPanels that have buttons and other components that will trigger events. I wish for these events to effect other panels, in the Hierachy of my program:
MainFrame(MainPanel(LeftPanel, RightPanel, CanvasPanel))
Sorry I couldnt indent to show the hierarchy. Here LeftPanel, RightPanel and CanvasPanel are objects that are created in the MainPanel. For example i want an event to trigger a method in another class e.g. LeftPanel has a button that will call a method in CanvasPanel. I have tried creating an EventListner in the MainPanel that would determine the source and then send off a method to the relevant class, but the only listeners that respond are the ones relevant to the components of class. Can I have events that will be listened to over the complete scope of the program? or is there another way to have a component that can call a method in the class that as an object, it has been created in.
Just as an example LeftPanel has a component to select the paint tool (its a simple drawing program) that will change a color attribute in the CanvasPanel object. Of course I realize i could have one massive Class with everything declared in it, but I'd rather learn if it is possible to do it this way!
Thanks in advance for any help you can offer
Lawrence
Edited by: insertjokehere on Apr 15, 2008 12:24 PM

Answer 1

Thanks for the response, ive added ActionListneres in the class where the component is, and in an external class. The Listeners work inside the class, but not in the external class
import java.awt.event.ActionEvent;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
public class LeftPanel extends JPanel implements ActionListener {  
    /* Constructing JButtons, null until usage of the constructor */
    JButton pencilBut;
    JButton eraserBut;
    JButton textBut;
    JButton copyBut;
    JButton ssincBut;
    JButton ssdecBut;
    ActionListener a = new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            System.out.print("\nNot supported yet.");
    /* The Top Panel contains the title of program */
    public LeftPanel(Dimension d){
        /* Sets up the layout for the Panel */
        BoxLayout blo = new BoxLayout(this,BoxLayout.Y_AXIS);
        this.setLayout(blo);
        /* Sets Up the Appearance of the Panel */
        this.setMinimumSize(d);
        this.setBackground(Color.RED);
        this.setBorder(BorderFactory.createLineBorder(Color.BLACK, 1));
        /* Pencil Tool */
        pencilBut = new JButton("Pencil");
        pencilBut.setAlignmentX(Component.CENTER_ALIGNMENT);
        pencilBut.setActionCommand("pencil");
        pencilBut.addActionListener(a);
        this.add(pencilBut);
        /* Eraser Tool */
        eraserBut = new JButton("Eraser");
        eraserBut.setAlignmentX(Component.CENTER_ALIGNMENT);
        eraserBut.addActionListener(a);
        this.add(eraserBut);
        /* Text Tool */
        textBut = new JButton("Text");
        textBut.setAlignmentX(Component.CENTER_ALIGNMENT);
        textBut.addActionListener(a);
        this.add(textBut);
        /* Copy Previous Page */
        copyBut = new JButton("Copy Page");
        copyBut.setAlignmentX(Component.CENTER_ALIGNMENT);
        copyBut.addActionListener(a);
        this.add(copyBut);
        /* Stroke Size Increase */
        ssincBut = new JButton("Inc");
        ssincBut.setAlignmentX(Component.CENTER_ALIGNMENT);
        ssincBut.addActionListener(a);
        this.add(ssincBut);
        /* Stroke Size Decrease */
        ssdecBut = new JButton("Dec");
        ssdecBut.setAlignmentX(Component.CENTER_ALIGNMENT);
        ssdecBut.addActionListener(a);
        this.add(ssdecBut);
        System.out.print("\nLeftPanel Completed");
    public void actionPerformed(ActionEvent e) {
        System.out.print("\nAction Performed");
    }But this is not picked up in my external class here
import java.awt.event.ActionEvent;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
public class MainPanel extends JPanel implements ActionListener {
    /* Creates a new the main JPanel that is used in the FlipBookFrame to contain all of the elements */
    public MainPanel(){
        /* TopPanel constraints*/
        tpcs.gridx = 1;
        tpcs.gridy = 0;
        tpcs.gridwidth = 1;
        tpcs.gridheight = 1;
        tpcs.fill = GridBagConstraints.BOTH;
        tpcs.weightx = 0.0;
        tpcs.weighty = 1.0;
        /* LeftPanel Constraints*/
        lpcs.gridx = 0;
        lpcs.gridy = 0;
        lpcs.gridwidth = 1;
        lpcs.gridheight = 3;
        lpcs.fill = GridBagConstraints.BOTH;
        lpcs.weightx = 1.0;
        lpcs.weighty = 1.0;
        /* CentrePanel Constraints*/
        cpcs.gridx = 1;
        cpcs.gridy = 1;
        cpcs.gridwidth = 1;
        cpcs.gridheight = 1;
        cpcs.fill = GridBagConstraints.NONE;
        cpcs.weightx = 0.0;
        cpcs.weighty = 0.0;
        /* RightPanel Constraints*/
        rpcs.gridx = 2;
        rpcs.gridy = 0;
        rpcs.gridwidth = 1;
        rpcs.gridheight = 3;
        rpcs.fill = GridBagConstraints.BOTH;
        rpcs.weightx = 1.0;
        rpcs.weighty = 1.0;
        /* BottomPanel Constraints*/
        bpcs.gridx = 1;
        bpcs.gridy = 2;
        bpcs.gridwidth = 1;
        bpcs.gridheight = 1;
        bpcs.fill = GridBagConstraints.BOTH;
        bpcs.weightx = 0.0;
        bpcs.weighty = 1.0;   
        this.setLayout(gblo);   //Sets the Layout of the panel to a GridBagLayout
        this.add(tp, tpcs); //Adds the TopPanel to the MainPanel using the TopPanel layout
        this.add(lp, lpcs); //Adds the LeftPanel to the MainPanel using the LeftPanel layout
        this.add(cp, cpcs); //Adds the CanvasPanel to the MainPanel using the CanvasPanel layout
        this.add(rp, rpcs); //Adds the RightPanel to the MainPanel using the RightPanel layout
        this.add(bp, bpcs); //Adds the BottomPanel to the MainPanel using the BottomPanel layout
        gblo.layoutContainer(this); //Lays Out the Container
    public PanelSizes getPanelSizes(){
        return ps;
    public void actionPerformed(ActionEvent e) {
        System.out.print("\nExternal Class finds event!");
        /*String command = e.getActionCommand();
        if (command.equals("pencil")){
            System.out.print("\nYESSSSSSSSSSSSSSSSSSSSS!");
    /* Create of objects using the PanelSizes funtions for defining the */
    PanelSizes ps = new PanelSizes();   //Creates a new PanelSizes object for sizing the panel
    CanvasPanel cp = new CanvasPanel(ps.getCentrePanelDimension()); //Creates a new Canvas Panel
    TopPanel tp = new TopPanel(ps.getHorizontalPanelDimension()); //Creates the TopPanel
    BottomPanel bp = new BottomPanel(ps.getHorizontalPanelDimension()); //Creates the BottomPanel
    LeftPanel lp = new LeftPanel(ps.getVerticalPanelDimension()); //Creates the LeftPanel
    RightPanel rp = new RightPanel(ps.getVerticalPanelDimension());   //Creates the RightPanel
    /* I have chosen to create individual constraints for each panel to allow for adding of all
     components a the end of the constructor. This will use slightly more memory but gives clarity
     in the code */
    GridBagConstraints cpcs = new GridBagConstraints();
    GridBagConstraints tpcs = new GridBagConstraints();
    GridBagConstraints bpcs = new GridBagConstraints();
    GridBagConstraints lpcs = new GridBagConstraints();   
    GridBagConstraints rpcs = new GridBagConstraints();
    GridBagLayout gblo = new GridBagLayout();
}Any help will be greatly appreciated :-)