Java切换按钮

Question

I have a Swing JFrame panel with 2 text fields and a single button. I need the button to be able to trigger a change in the text in the different text fields (specifically, from "On" to "Off"). The complicating factor is I need it to only change the text of the last text area that was clicked.

Below is my code so far. Notice that clicking the text fields themselves toggles the text, which I want. But I also want the button to toggle the text - but only the text in the last text area the user clicked before clicking the button. The way I have it now the button toggles both text fields, which I don't want.

I suspect there may be a simple way to implement this that I'm overlooking.

public class SwitchesTest extends JFrame {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new SwitchesTest().displayJFrame();
            }
        });
    }

    private void displayJFrame() {
        JFrame frame = new JFrame("Switches");

        JButton button = new JButton("Switch");
        JTextArea switch1 = new JTextArea("On",1,3);
        JTextArea switch2 = new JTextArea("On",1,3);

        frame.getContentPane().setLayout(new GridBagLayout());

        frame.add(switch1);
        frame.add(switch2);
        frame.add(button);

        button.addActionListener(e -> {
            switch1.setText("On".equals(switch1.getText()) ? "Off" : "On");
            switch2.setText("On".equals(switch2.getText()) ? "Off" : "On");
        });

        switch1.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                switch1.setText("On".equals(switch1.getText()) ? "Off" : "On");
            }
        });

        switch2.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                switch2.setText("On".equals(switch2.getText()) ? "Off" : "On");
            }
        });

        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

Answer 1

Not tested, but just save the last text area clicked so you can toggle it later.

Note: using "static" here is starting to be an anti-pattern, imo. Consider switching this class to an object that is instantiated and initializes itself completely in its ctor.

public class SwitchesTest {

   static private JTextArea lastClicked;

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

    static void displayJFrame() {
        JFrame frame = new JFrame("Switches");

        JButton button = new JButton("Switch");
        JTextArea switch1 = new JTextArea("On",1,3);
        JTextArea switch2 = new JTextArea("On",1,3);

        frame.getContentPane().setLayout(new GridBagLayout());

        frame.add(switch1);
        frame.add(switch2);
        frame.add(button);

        button.addActionListener(e -> {
            if( lastClicked != null ) 
              lastClicked.setText("On".equals( lastClicked.getText()) ? "Off" : "On");
        });

        switch1.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                switch1.setText("On".equals(switch1.getText()) ? "Off" : "On");
            lastClicked = switch1;
            }
        });

        switch2.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                switch2.setText("On".equals(switch2.getText()) ? "Off" : "On");
            lastClicked = switch2;
            }
        });

Answer 2

But I also want the button to toggle the text - but only the text in the last text area the user clicked before clicking the button.

Text components already have an API to track which text component last had focus so there is no need to manage this on your own.

All you need to do us use a TextAction for the ActionListener. Then you just use the getFocusedComponent() method of the TextAction to access the last text component that had focus.

Something like:

button.addActionListener( new TextAction("Switch")
{
    @Override
    public void actionPerformed(ActionEvent e)
    {
        JTextComponent component = getFocusedComponent();

     if( component != null )
       component.setText("On".equals( component.getText()) ? "Off" : "On");
 }
});

Of course focus will be for any text component on the frame, so this approach will only work if you only have the two text components.

But with this approach there is no need for any extra listeners.