当执行JButton ActionEvent时，如何通知具有GUI构建器类实例的类

Question

Ok, here is my problem. Class B is a class that build a GUI ,which has a textField and button. class A has an instance of class B.Now I enter some value in the textfield, when I click the button, in class AI want to print out the value I just enter in the textfield, how can I achieve that?

Code below may better explain what I want to achieve:

    public class A
    {
        B myB = new B();

        (when the JButton was clicked, 
         how can I get the new textfield value here?)
    }

    public class B
    {
        JLabel myLabel;
        JButton myButton;

        public B()
        {
            getContentPane().setLayout(null);
            myLabel = new JLabel();
            myLabel.setLocation(0,0);
            myLabel.setSize(100,30);
            myLabel.setBackground( new Color(-6710887) );
            myLabel.setText("");
            getContentPane().add(myLabel);

            myButton = new JButton();
            myButton.setLocation(0,50);
            myButton.setSize(100,30);
            myButton.setBackground( new Color(-16737895) );
            myButton.setText("Submit");
            getContentPane().add(myButton);

            myButton.addActionListener(this);

            setSize(400,400);
            setVisible(true);
            setResizable(false);

            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        }

        public void actionPerformed(ActionEvent e)
        { 

              (how can I pass this "myLabel.getText()" value to class A when 
              this action performed?)
        }
    }

Can anybody help me finish this little program? Thanks in advance!

Answer 1

You need to expose the value in text field with a method in class B. Then class A can call that method. What it actually sounds like though is that class A (or something else) should be a ActionListener for your button.

However, a bigger problem is that you don't have a text field you just have a label in class B. This code is a good reason why you shouldn't use a GUI builder, especially when learning Swing.

Some reading: http://docs.oracle.com/javase/tutorial/uiswing/components/textfield.html http://docs.oracle.com/javase/tutorial/uiswing/events/

Answer 2

I often make an "App" class that ties all my GUI-builder-built components together. Any GUI builder worth anything lets you add getters to the generated source code. Add some getters to the GUI-built components to retrieve key elements of the GUI, then let the App class use the getters to interact with the components as necessary. This won't win any MVC/MVVM/MVP design awards, but it gets the job done, which ought to count for something.

public class App {
    private B _b;

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                App app = new App();
                app.run();
            }
        });
    }

    void run() {
        _b = new B();
        _b.getMainButton().addActionListener(new MainButtonListener());
        _b.setVisible(true);
    }

    private void handleMainButtonClicked() {
        String mainText = _b.getMainTextArea().getText();
        System.out.println("Button clicked; main text = " + mainText);
    }

    public class MainButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            handleMainButtonClicked();
        }
    }
}

public class B extends JFrame {
    private JPanel _contentPane;
    private JTextArea _jTextArea;
    private JButton _jButton;

    public B() {
        initComponents();
    }

    private void initComponents() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(400, 400);
        _contentPane = new JPanel();
        setContentPane(_contentPane);

        _jTextArea = new JTextArea();
        _contentPane.add(_jTextArea, BorderLayout.CENTER);

        _jButton = new JButton("My Button");
        _contentPane.add(_jButton, BorderLayout.SOUTH);
    }

    public JButton getMainButton() {
        return _jButton;
    }

    public JTextComponent getMainTextArea() {
        return _jTextArea;
    }
}