JPanel is added onto other Jpanel on togglebutton

问题:

I am trying to make a popup panel which is activated with the help of JToggleButton. I want the JPanel to be added onto the other Jpanel when ToggleButton is selected and hides when the ToggleButton is deselected.

I have declared the JToggleButton and used ItemListener. But What is happening is when i select the ToggleButton a panel is created if i deselect and Select it again another JPanel is added again and so on and After 5 clicks , Nothing appears.

public static JPanel createDesignButtons(){
    designButtonsPanel.setOpaque(false);
    BoxLayout boxLayout = new BoxLayout(designButtonsPanel, BoxLayout.LINE_AXIS);
    designButtonsPanel.setLayout(boxLayout);

    mainButton.setIcon(Icons.venueIcon);
    mainButton.setBorderPainted(false);
    mainButton.setPreferredSize(new Dimension(40,40));
    mainButton.addItemListener(new ItemListener() {
    public void itemStateChanged(ItemEvent ev) {
        if(ev.getStateChange()==ItemEvent.SELECTED){
        designButtonsPanel.add(createButtonsDialog());
        designButtonsPanel.validate();
        } else if(ev.getStateChange()==ItemEvent.DESELECTED){
        System.out.println("button is not selected");
        }
    }
});
    designButtonsPanel.add(mainButton);

    JLabel padding = new JLabel(" ");
    padding.setPreferredSize(null);

    JLabel divider = new JLabel("", Icons.dividerIcon, JLabel.CENTER);
    divider.setPreferredSize(new Dimension(3,45));
    designButtonsPanel.add(divider);


    SwingUtilities.updateComponentTreeUI(designButtonsPanel);
    return(designButtonsPanel);
}

The above code is showing the mainButton is togglebutton that i want action on and the DesignButtonPanel is the Panel which is parent.

public static JPanel createButtonsDialog(){

    JPanel buttonsPanel = new JPanel();
    buttonsPanel.setBorder(new LineBorder(Color.gray,1));
    return buttonsPanel;
}

This class show the panel i would like to add onto parent panel

How can i get the Panel added only once when the JtoggleButton is Selected and hides when its Deselected?

回答1:

The problem is you keep creating instances of your JPanel. You could remove the JPanel if your JToggleButton is not selected and add an already created instance of your JPanel if the button is selected. See this simple example:

public class MainFrame extends JFrame {

private JPanel topPanel = new JPanel();
private JPanel centerPanel = new JPanel();
private JToggleButton toggleButton = new JToggleButton("Toggle");

public MainFrame() {
    this.setVisible(true);
    this.setDefaultCloseOperation(EXIT_ON_CLOSE);
    this.setLayout(new BorderLayout());

    this.topPanel.setPreferredSize(new Dimension(100, 100));
    this.centerPanel.setPreferredSize(new Dimension(100, 100));
    this.toggleButton.setPreferredSize(new Dimension(100, 100));

    this.add(topPanel, BorderLayout.NORTH);
    this.add(centerPanel, BorderLayout.CENTER);
    this.add(toggleButton, BorderLayout.SOUTH);

    this.toggleButton.addItemListener(new ItemListener() {
        @Override
        public void itemStateChanged(ItemEvent e) {
            if(e.getStateChange() == ItemEvent.SELECTED) {
                add(centerPanel, BorderLayout.CENTER);
            } else {
                remove(centerPanel);
            }
            pack();
        }
    });

    this.pack();
    this.setVisible(true);
}
}

You can see that centerPanel is only instantiated once.