JPanel 不显示组件

Question

让我们从一些背景开始，这是第一年的拼贴项目。 GUI 是这样构建的，接口处理程序调用所有 JPanel 并将它们放在正确的位置。这是为了结构，所以很容易维护。

问题是保存菜单的面板在添加后不显示它的组件。我将包含一些图像，以便更容易理解。

有问题的面板称为 MenuPanel。

所以这里是登录按钮，目前只清除内容面板，然后添加菜单面板。

Login page where the button is located

这里的菜单面板是空的

here is the menu panel all empty

代码 接口处理程序 你可以看到我已经在 menu 方法中弄乱了 .repaint() 方法。 公共类接口处理程序 {

private static InterfaceHandler singleton;

/**
 * Checks if there is already a instance running of InterfaceHandler if so
 * return the instance if not create a instance.
 *
 * @return Instance
 */
public static InterfaceHandler instance() {
    if (singleton == null) {
        singleton = new InterfaceHandler();
    }

    return singleton;
}

private ContentPanel contentPanel;
private LoginPanel loginPanel;
private MainFrame mainFrame;
private MainPanel mainPanel;
private MenuPanel menuPanel;

/**
 * Initializes default Interface
 */
public InterfaceHandler() {
    initComponents();

}

/**
 * Initializes GUI Components that will be needed now or in the future.
 */
public void initComponents() {
    mainFrame = new MainFrame();
    mainPanel = new MainPanel();
    contentPanel = new ContentPanel();
    loginPanel = new LoginPanel();
    menuPanel = new MenuPanel();

    contentPanel.setBounds(100, 100, 860, 700);
    menuPanel.setBounds(10, 10, 80, 400);
    loginPanel.setBounds(280, 250, 300, 200);

    mainFrame.add(mainPanel);
    mainPanel.add(contentPanel);

    mainFrame.setVisible(true);
    contentPanel.add(loginPanel);
}

/**
 * Clears the ContentPanel of all components
 */
public void clear() {
    System.out.println("Clear Ran");
    contentPanel.removeAll();
    contentPanel.repaint();
}

/**
 * Adds the Login Screen.
 */
public void login() {
    System.out.println("Login Ran");
    contentPanel.add(loginPanel);
    contentPanel.repaint();
}

/**
 * Adds the menu.
 */
public void menu() {
    System.out.println("Menu Ran");
    mainPanel.sidePanel.add(menuPanel);
    menuPanel.repaint();
    mainPanel.repaint();
    mainPanel.sidePanel.repaint();
}

}

这里是面板的代码，大部分是由 netbeans 设计编辑器自动生成的。 所以很丑（对不起）

公共类 MenuPanel 扩展 javax.swing.JPanel {

/**
 * Creates new form MenuPanel
 */
public MenuPanel() {
    initComponents();
}

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    jLabel1 = new javax.swing.JLabel();
    jSeparator1 = new javax.swing.JSeparator();
    jLabel2 = new javax.swing.JLabel();
    baggageButton = new javax.swing.JLabel();

    jLabel1.setBackground(new java.awt.Color(204, 204, 204));
    jLabel1.setFont(new java.awt.Font("Tahoma", 0, 13)); // NOI18N
    jLabel1.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);
    jLabel1.setText("Menu");

    jSeparator1.setBackground(new java.awt.Color(204, 204, 204));

    baggageButton.setFont(new java.awt.Font("Tahoma", 0, 12)); // NOI18N
    baggageButton.setText("Baggage");

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
    this.setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(jSeparator1)
                .addComponent(jLabel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(baggageButton, javax.swing.GroupLayout.PREFERRED_SIZE, 80, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(jLabel2, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
            .addContainerGap())
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 22, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(0, 0, 0)
            .addComponent(jSeparator1, javax.swing.GroupLayout.PREFERRED_SIZE, 4, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
            .addComponent(baggageButton, javax.swing.GroupLayout.PREFERRED_SIZE, 53, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(18, 18, 18)
            .addComponent(jLabel2, javax.swing.GroupLayout.PREFERRED_SIZE, 53, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
    );
}// </editor-fold>                        

// Variables declaration - do not modify                     
private javax.swing.JLabel baggageButton;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JSeparator jSeparator1;
// End of variables declaration                   
}

澄清一下，方法菜单是从不同的类调用的。

Answer 1

如果要向已经可见的面板添加组件，则需要调用validate()。

public void menu() {
    System.out.println("Menu Ran");
    mainPanel.sidePanel.add(menuPanel);

    mainPanel.sidePanel.validate();  // try this

    menuPanel.repaint();
    mainPanel.repaint();
    mainPanel.sidePanel.repaint();
}

Answer 2

（这个答案是错误的，但随后的 cmets 确实有助于理解为什么 @whiskeyspider 的答案是正确的）

在这段代码中：

mainFrame.add(mainPanel);
mainPanel.add(contentPanel);

mainFrame.setVisible(true);
contentPanel.add(loginPanel);

您不会在任何地方添加menuPanel。它在menu() 方法中添加（为时已晚），但未被调用。