如何将组件放在 CardLayout 面板的中心

how to put components in the center in a CardLayout panel

我有一个包含几个面板的框架,它们由 CardLayout 改变。 在每个面板内,我将有不同的组件。为了设计面板的 GUI,我使用了 GridBagLayout。但问题是我用于这些面板的任何组件或布局,它们都位于页面顶部。所以基本上 CardLayout 的面板大小是框架的一小部分。我想让子面板的大小与主 CardLayout 的大小一样大。

主要 CardLayout 代码:

public class MainPanel extends JPanel {
    private CardLayout cl = new CardLayout();
    private JPanel panelHolder = new JPanel(cl);

    public MainPanel() {
        NewSession session = new NewSession(this);
        ChooseSource chooseSource = new ChooseSource(this);

        panelHolder.add(session, "1");
        panelHolder.add(chooseSource, "2");

        cl.show(panelHolder, "dan");
        add(panelHolder);
    }
    public void showPanel(String panelIdentifier){
        cl.show(panelHolder, panelIdentifier);
    }
}

子面板:

public class ChooseSource extends JPanel {
    MainPanel ob2;
    JButton btn;
    JLabel label;
    JTextField field;

    public ChooseSource(MainPanel mainPanel){
        this.ob2 = mainPanel;


        btn = new JButton("Browse");
        label = new JLabel("Folder ");
        field = new JTextField();

        btn.addActionListener(new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e){
                ob2.showPanel("1");

            }
        });


        GridBagLayout layout = new GridBagLayout();
        setLayout(layout);

        GridBagConstraints c = new GridBagConstraints();

        c.fill = GridBagConstraints.HORIZONTAL;
        c.gridx = 0;
        c.gridy = 0;
        c.ipady = 20;
        c.gridheight = 2;
        add(btn, c);

        c.fill = GridBagConstraints.HORIZONTAL;
        c.gridx = 1;
        c.gridy = 0;
        c.ipady = 10;
        c.gridheight = 1;
        c.insets = new Insets(0,10,0,0); 
        add(label, c);

        c.fill = GridBagConstraints.HORIZONTAL;
        c.gridx = 1;
        c.gridy = 1;
        c.ipady = 0;
        c.gridheight = 1;
        c.insets = new Insets(0,10,0,0); 
        add(field, c);
    }
}

左图不是,右图是我想做的。基本上我想访问面板的所有可用 space。

有什么想法吗?

MainPanel 的布局管理器更改为 BorderLayoutGridBagLayout