Handling events between classes

Question

I have a main class with an Editor class (with a JTextPane) and a Toolbar class (with a JList and a Jbutton, I don't want to use JToolBar). These two classes are composed by many components and I would like not to mix them into the same class. I want the editor and the toolbar to communicate. Let's say I write "Hello" in the toolbar and then click on Submit. I want the text pane to show me "Hello". I build the classes this way:

public class Main{
    public MainGUI(){
        initComponents();
    }

    private void initComponents(){
        JFrame mainframe=new JFrame("Main Frame");
        Editor editor=new Editor();
        Toolbar toolbar=new Toolbar();
        mainframe.getContentPane().setLayout(new BorderLayout());
        mainframe.getContentPane().add(editor, BorderLayout.CENTER);
        mainframe.getContentPane().add(toolbar, BorderLayout.NORTH);
        mainframe.setVisible(true);
    }
}

public class Editor extends JPanel{
    public Editor(){
        super();
        initComponents();
    }

    private void initComponents(){
        JTextPane textpane=new JTextPane();

        this.setLayout(new BorderLayout());
        this.add(textpane, BorderLayout.CENTER);
    }
}

public class Toolbar extends JPanel{
    public Toolbar(){
        super();
        initComponents();
    }

    private void initComponents(){
        JTextField textfield=new JTextField();
        JButton submitbutton=new JButton("Submit");

        this.setLayout(newFlowLayout());
        this.add(textfield);
        this.add(submitbutton);
    }
}

How should I implement the event handling betweenthe Toolbar and the Editor?

Answer 1

The key principal is to pass references as appropriate so that each object can access the objects it needs.

For example, if your "submit" means to append the text in the text field (that you have in your toolbar) to the editor's text pane, then you could do the following:

public class Main{
    public MainGUI(){
        initComponents();
    }

    private void initComponents(){
        JFrame mainframe=new JFrame("Main Frame");
        Editor editor=new Editor();
        Toolbar toolbar=new Toolbar(editor);
        mainframe.getContentPane().setLayout(new BorderLayout());
        mainframe.getContentPane().add(editor, BorderLayout.CENTER);
        mainframe.getContentPane().add(toolbar, BorderLayout.NORTH);
        mainframe.setVisible(true);
    }
}

private final JTextPane textpane=new JTextPane();
public class Editor extends JPanel{
    public Editor(){
        super();
        initComponents();
    }

    private void initComponents(){
        this.setLayout(new BorderLayout());
        this.add(textpane, BorderLayout.CENTER);
    }

    public void appendText(final String text) {
        this.textpane.setText( this.textpane.getText()+text );
    }
}

public class Toolbar extends JPanel{
    private final Editor editor;
    public Toolbar(final Editor editor){
        super();
        this.editor = editor;
        initComponents();
    }

    private void initComponents(){
        final JTextField textfield=new JTextField();
        JButton submitbutton=new JButton("Submit");
        submitbutton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(final ActionEvent event) {
                editor.appendText( textfield.getText() );
            }
            });

        this.setLayout(newFlowLayout());
        this.add(textfield);
        this.add(submitbutton);
    }
}

Answer 2

You can create an interface ValueSubmittedListener

interface ValueSubmittedListener {
    public void onSubmitted(String value);
}

and have Editor implements it.

class Editor implements ValueSubmittedListener{

    ...

    public void onSubmitted(String value) {
        // add text to JTextPane.
    }
}

Then have Toolbar provide methods

class Toolbar {

    private List<ValueSubmittedListener> listeners = new ArrayList<ValueSubmittedListener>();


    public void addListener(ValueSubmittedListener listener) {
        listeners.add(listener);
    }

    private void notifyListeners() {
        for (ValueSubmittedListener listener : listeners) {
            listener.onSubmitted(textfield.getText());
        }
    }

}

Then everytime you need to send new value to Editor (i.e: in submitButton's ActionListener), just invoke the method notifyListeners.

UPDATE:

I forgot to mention that in the initComponents of Main, you have to register Editor to Toolbar:

private void initComponents() {
   JFrame mainframe = new JFrame("Main Frame");
   Editor editor = new Editor();
   Toolbar toolbar = new Toolbar();
   toolbar.addListener(editor); // register listener
   ...
}