选择特定 JComboBox 项时如何向 JPanel 添加额外的 JButton

Question

我一直面临这个关于让我的 JCombobox 尽可能动态的小问题。
For an example, when a selected item in combobox is selected, it will dynamically change the number of buttons accordance to the number of days within the month and be added in the panel

我面临的问题是它不会自动更改面板的显示，但是当我尝试查看代码是否在我的控制台日志中运行时。它运行顺利。我尽我所能找到解决方案，但无济于事。

主要问题在 actionListener 中，例如，如果选择了 2 月，它将显示 28 个按钮，如果选择了 1 月，它将显示 31 天等，但是当我运行代码时，我的 system.out.println 状态它运行但我的 Gui 没有显示任何按钮。

private static JButton method_Btn(int i){

    JButton btn = new JButton(Integer.toString(i));

    return btn;

}

public static void day(){

    JFrame frame = new JFrame();

    JPanel topPanel = new JPanel();

    JPanel centerPanel = new JPanel();

    JButton days = new JButton();

    JLabel days_label = new JLabel();

    //-- Top Panel

    String month[] = {"--Select Month--" , "January", "February"};

    JComboBox month_combo = new JComboBox(month);

    topPanel.add(month_combo, BorderLayout.PAGE_START);

    //-- Center Panel

    centerPanel.setLayout(new FlowLayout());

    centerPanel.add(days_label);

    //------- Change when jcombo is selected

    month_combo.addActionListener(new ActionListener() {

        @Override

        public void actionPerformed(ActionEvent arg0) {

            if(month_combo.getSelectedItem().equals("January")){

                for(int i = 0;i < 31;i++){

                    centerPanel.add(method_Btn(i));

                }

            }

            if(month_combo.getSelectedItem().equals("February")){

                for(int i = 0;i < 28;i++){

                    centerPanel.add(method_Btn(i));

                }

            }

        }

    });

    frame.add(topPanel, BorderLayout.PAGE_START);

    frame.add(centerPanel , BorderLayout.CENTER);

    frame.setSize(400,400);

    frame.setVisible(true);

}

public static void main(String[] args){

    day();

}

附加说明，我意识到我面临的另一个问题是，它会在选择第二个月后创建按钮的数量。我如何解决它是我添加了 centerPanel.removeAll(); 和 centerPanel.repaint();

希望这可以帮助任何有需要的人。:)

Answer 1

您需要revalidate()添加的组件如下所示：centerPanel.revalidate();您需要更改以下代码：month_combo.addActionListener(new ActionListener() {&nbsp; &nbsp; @Override&nbsp; &nbsp; public void actionPerformed(ActionEvent arg0) {&nbsp; &nbsp; &nbsp; &nbsp; if(month_combo.getSelectedItem().equals("January")){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for(int i = 0;i < 31;i++){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; centerPanel.add(method_Btn(i));&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; if(month_combo.getSelectedItem().equals("February")){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for(int i = 0;i < 28;i++){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; centerPanel.add(method_Btn(i));&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; centerPanel.revalidate(); // Need to add this for revalidation for the component&nbsp; &nbsp; }});