wrong parent for CardLayout in java

问题

I want to change cards in my CardLayout (which contains labels) for every choice in my combo box. So when I select Item2 in the combo box it should show the second card but it returns error instead.

Inside the method initComponents() I successfully showed the first card using cardLayout.show(imagePanel, "1"); but when I tried to do the same inside private void comboMenuActionPerformed(), it returns the error "IllegalArgumentException: wrong parent for CardLayout". Why is this happening?

public class MyFrame extends JFrame {
    public MyFrame() {
        initComponents();
    }
    private void initComponents() {
        cardLayout = new java.awt.CardLayout(); 
        mainPanel = new javax.swing.JPanel();
        centerPanel = new javax.swing.JPanel();
        imagePanel = new javax.swing.JPanel(cardLayout);
        comboMenu = new javax.swing.JComboBox<>();
        JLabel firstPicture = new JLabel("");
        JLabel secondPicture = new JLabel("");
        ...

        firstPicture.setIcon(...);
        secondPicture.setIcon(...); 

        imagePanel.add(firstPicture, "1");
        imagePanel.add(secondPicture, "2");
        String[] menu = {"Item1", "Item2", "Item3"};

        cardLayout.show(imagePanel, "1"); //this works fine

        imagePanel.setLayout(new java.awt.CardLayout());
        centerPanel.add(imagePanel);

        comboMenu.setModel(new javax.swing.DefaultComboBoxModel<>(menu));

        mainPanel.add(centerPanel);
    }

    private void comboMenuActionPerformed(java.awt.event.ActionEvent evt) {                                           
        if(comboMenu.getSelectedItem().toString().equals("Item2")) {
            cardLayout.show(imagePanel, "2"); //WHY THIS DOESN'T WORK
        }
    }

    public static void main(String args[]) {
            java.awt.EventQueue.invokeLater(new Runnable() {
                public void run() {
                    new MyFrame().setVisible(true);
                }
        });
    }
    private javax.swing.JComboBox<String> comboMenu;
    private javax.swing.JPanel centerPanel;
    private javax.swing.JPanel imagePanel;
    private javax.swing.JPanel mainPanel;
    private java.awt.CardLayout cardLayout;
}

回答1:

    imagePanel = new javax.swing.JPanel(cardLayout);
    ...
    cardLayout.show(imagePanel, "1"); //this works fine
    imagePanel.setLayout(new java.awt.CardLayout());

You replace the layout of the image panel with a new instance of the CardLayout. Get rid of the last statement:

    //imagePanel.setLayout(new java.awt.CardLayout());

回答2:

You assign the card layout to imagePanel by:

imagePanel = new javax.swing.JPanel(cardLayout);

But then you assign a new card layout by:

imagePanel.setLayout(new java.awt.CardLayout());

This overwrites the first card layout to which you added the labels.

来源：https://stackoverflow.com/questions/60611409/wrong-parent-for-cardlayout-in-java

标签

java

swing

awt

layout-manager

cardlayout