在执行按钮操作期间删除按钮

Question

I was trying to figure out why my program freezes and I was able to replicate it with a small script so I can put it here. Basically, in this script When you clicked on button Test1, it is supposed to remove it and added new button Test2. The program freezes. Why? How can I over come this?

final JFrame frame = new JFrame("FrameDemo");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setPreferredSize(new Dimension(800, 600));

                final JPanel panel = new JPanel();
                final JButton bTest1 = new JButton("test1");
                bTest1.addActionListener(new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent e) {
                      panel.remove(bTest1);
                      panel.add(new JButton("test2"));
                    }

                });
                panel.add(bTest1);
                frame.getContentPane().add(panel);

                frame.pack();
                frame.setVisible(true);

Offcourse in the real program, on the button click, remove all the contents of the panel and re add a new set of components.

Looking for your help!

Answer 1

Offcourse in the real program, on the button click, remove all the contents of the panel and re add a new set of components.

Then you should probably be using a CardLayout . A CardLayout is designed to allow you to swap panels.

Read the section from the Swing tutorial on How to Use CardLayout for more information and working examples.

The program freezes. Why? How can I over come this?

It doesn't freeze, its just that the panel isn't smart enough to repaint itself. It you resize the frame you will see the new button.

The problem is you remove the button and add a new button but the panel never repaints itself because the panel is not aware of the changes. You need to invoke the layout manager so the new button can be given a proper size.

The basic code for add/removing components on a visible GUI is:

panel.remove(...);
panel.add(...);
panel.revalidate();
panel.repaint(); // sometimes needed

Answer 2

Action performed method of the JButton will be executed in AWT thread. When you remove the button from the container, that will launch events that should be executed as well in the same thread. So one is waiting for the other , and so the program freezes. For solving that situation use

SwingUtilities.invokeLater

method to execute the removing action of your button