Add dynamic buttons to jpanel in Java

问题

I'm trying to do a program in Java that will make a button appears in a JPanel where and when it's clicked. To do that, I have the method run, with the following code:

 public void run(){
    panel.addMouseListener(new MouseAdapter() {
        public void mousePressed(MouseEvent e){
            JButton button = new JButton();
            button.setVisible(true);
            button.setAlignmentX(e.getXOnScreen());
            button.setAlignmentY(e.getYOnScreen());
            panel.add(button);
            panel.revalidate();
            panel.repaint();
        }
    });
}

The problem is, nevermind where I click, the buttons never appears.

回答1:

This code should make a button appear when the panel is clicked. It will not make it appear at the cursor but that should be easy to add. It will also make a new button every time you click the panel. If you only want one button simply move this line JButton button = new JButton();, outside of the mousePressed event

public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.setSize(500, 500);
    JPanel panel = new JPanel();
    panel.setSize(500, 500);
    frame.add(panel);
    frame.show();
    run(panel);
}

 public static void run(JPanel panel){
        panel.addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent e){
                JButton button = new JButton();
                button.setVisible(true);                 
                panel.add(button);
                panel.revalidate();
            }
       });
}

回答2:

a button appears in a JPanel where and when it's clicked.

button.setAlignmentX(e.getXOnScreen());
button.setAlignmentY(e.getYOnScreen());

You are using a couple of incorrect methods.

To position a component in a panel you need to use:

button.setLocation(...);

However, you can't use the getXOnScreen() method because that is relative to the screen. You need to position the component relative to the panel. So instead you need to use:

button.setLocation(e.getX(), e.getY());

That is still not enough because when you use a null layout you also are responsible for determining the size of the component. So you would also need to use:

button.setSize( button.getPreferredSize() );

You also need to make sure the panel is using a null layout, otherwise the layout manager will override the size/location.

回答3:

This worked for me (even whithout adding buttons labels)

public static void main(String[] args) {

        final JPanel panel = new JPanel();

        JFrame frame = new JFrame("test swing");
        frame.setAlwaysOnTop(true);
        frame.setSize(400, 200);
        frame.add(panel);
        frame.setVisible(true);

        panel.addMouseListener(new MouseAdapter() {

            @Override
            public void mousePressed(MouseEvent e){
                JButton button = new JButton();
                button.setVisible(true);
                button.setAlignmentX(e.getXOnScreen());
                button.setAlignmentY(e.getYOnScreen());
                panel.add(button);
                panel.revalidate();
                panel.repaint();
            }
        });
    }

来源：https://stackoverflow.com/questions/30465297/add-dynamic-buttons-to-jpanel-in-java

标签

java

swing

jpanel

jbutton