Question

我有一个由各种不同的JPanel组成的CardLayout，我随意展示。此GUI链接到后端，GUI的目的是允许用户操作存储在后端的数据。

问题是，当用户更改后端中的某些数据时，我的JLabel并未反映该数据的变化。我知道这是因为JLabel初始化了一次，当我更新它们初始化的变量时，我必须再次调用setText才能让它们体验到这种变化。

示例：以下是我的JLabel初始化方式

CurrentBAName = new javax.swing.JLabel();
CurrentBAName.setText(GUI.currentBankAccount.getAccountName());

问题是，当我更改GUI.currentBankAccount.getAccountName()的值时，我的JLabel上的文本不会更新。我到处都有像这样的JLabel，每次用户做出任何改变时都必须经历并手动调用setText会很痛苦。有什么方法可以让JLabel在该变量的值发生变化时自动更新？

也许我可以实现某种Observer模式？我如何用JLabels做到这一点？
或者也许我可以使用focusGained事件，以便每次切换到面板时，focusGained事件都会触发，以便我可以更新内容。我不知道如何做到这一点，我不确定焦点如何与CardLayout一起使用。也许只是每次我使用layout.show(..)显示面板时调用的方法。我该如何实现呢？还有更好的方法吗？

更新：示例代码

GUI.java是我的主要GUI类，它将包含一个JPanel，我的所有页面都将随意添加和显示。

import javax.swing.*;

public class GUI extends javax.swing.JFrame
{
    public static String item;
    private javax.swing.JPanel MainPanel;

    public GUI()
    {
        // creates a JPanel called MainPanel which will hold the cards
        // in my CardLayout
        initComponents();
    }

    private void initComponents()
    {

        MainPanel = new javax.swing.JPanel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        MainPanel.setBackground(new java.awt.Color(198, 118, 38));
        MainPanel.setMaximumSize(new java.awt.Dimension(1000, 1000));
        MainPanel.setName(""); // NOI18N
        MainPanel.setPreferredSize(new java.awt.Dimension(1024, 768));
        MainPanel.setLayout(new java.awt.CardLayout());

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
                layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                        .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                        .addComponent(MainPanel, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addContainerGap())
        );
        layout.setVerticalGroup(
                layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                        .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                        .addComponent(MainPanel, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addContainerGap())
        );

        pack();
        setLocationRelativeTo(null);

    }

    // Grab the panel that was created in initComponents() so that I can add
    // other panels to it
    public JPanel getMainPanel()
    {
        return MainPanel;
    }

    public static void main(String args[])
    {
        java.awt.EventQueue.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                GUI mainGUI = new GUI();

                // The JLabel in DisplayPanel.java will initially say root
                item = "root";

                JPanel cardHolder = mainGUI.getMainPanel();
                //This panel contains a button which will update the name of
                //the currentUserAccount
                MainMenuPanel mainMenu = new MainMenuPanel(cardHolder);
                cardHolder.add(mainMenu, "MainMenu");

                //This panel holds a JLabel that I want to have updated automatically
                //when the user presses the button on MainMenuPanel
                DisplayPanel display = new DisplayPanel(cardHolder);
                cardHolder.add(display, "Display");

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

DisplayPanel.java将是一个带有JLabel的JPanel，我希望在其上更新

import java.awt.*;
import javax.swing.*;

public class DisplayPanel extends javax.swing.JPanel
{
    private JPanel MainPanel;

    public DisplayPanel(JPanel MainPanel)
    {

        this.MainPanel = MainPanel;
        initComponents(); // Creates my panel with the JLabels/buttons etc
    }

    @SuppressWarnings("unchecked")                 
    private void initComponents()
    {

        jLabel1 = new javax.swing.JLabel();
        GoToMainMenuButton = new javax.swing.JButton();

        jLabel1.setFont(new java.awt.Font("Tahoma", 0, 18)); // NOI18N
        jLabel1.setText(GUI.item); // sets the JLabel to the GUI.item variable

        GoToMainMenuButton.setText("Go to MainMenuPanel");
        GoToMainMenuButton.addMouseListener(new java.awt.event.MouseAdapter()
        {
            public void mouseClicked(java.awt.event.MouseEvent evt)
            {
                GoToMainMenuButtonMouseClicked(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
        this.setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addContainerGap(269, Short.MAX_VALUE)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(GoToMainMenuButton)
                    .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 145, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(266, 266, 266))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(168, 168, 168)
                .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 63, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(83, 83, 83)
                .addComponent(GoToMainMenuButton)
                .addContainerGap(116, Short.MAX_VALUE))
        );
    }                       

    private void GoToMainMenuButtonMouseClicked(java.awt.event.MouseEvent evt)                                                
    {
        // go back to the MainPanel                                        
        CardLayout layout = (CardLayout) (MainPanel.getLayout());
        layout.show(MainPanel, "MainMenu");
    }                                               

    private javax.swing.JButton GoToMainMenuButton;
    private javax.swing.JLabel jLabel1;

}

MainMenuPanel.java将是一个带有按钮的JPanel，按下该按钮时，将更新DisplayPanel中JLabel文本设置为的变量。

import java.awt.*;
import javax.swing.*;

public class MainMenuPanel extends javax.swing.JPanel
{

    private JPanel MainPanel;

    public MainMenuPanel(JPanel MainPanel)
    {

        this.MainPanel = MainPanel;
        initComponents(); // Creates my panel with the JLabels/buttons etc
    }

    @SuppressWarnings("unchecked")                        
    private void initComponents()
    {

        GoToDisplayPanelButton = new javax.swing.JButton();

        GoToDisplayPanelButton.setText("Press Me");
        GoToDisplayPanelButton.addMouseListener(new java.awt.event.MouseAdapter()
        {
            public void mouseClicked(java.awt.event.MouseEvent evt)
            {
                GoToDisplayPanelButtonMouseClicked(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
        this.setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(252, 252, 252)
                .addComponent(GoToDisplayPanelButton)
                .addContainerGap(260, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addContainerGap(198, Short.MAX_VALUE)
                .addComponent(GoToDisplayPanelButton)
                .addGap(175, 175, 175))
        );
    }                      

    private void GoToDisplayPanelButtonMouseClicked(java.awt.event.MouseEvent evt)                                                    
    {                                                        
        // Changes the value of item. I want this change to be reflected on my
        // JLabel in DisplayPanel.java, but it is not because I do not explicitly
        // call setText on the JLabel here. I am wondering if there is a way to 
        // have my JLabel automatically update when the variable in its setText
        // is changed, without having to directly call setText. Or some other 
        // way to update it without calling setText every time I change something.
        GUI.item = "new value";

        // Switches to my DisplayPanel which should show the updated name in its JLabel
        CardLayout layout = (CardLayout)(MainPanel.getLayout());
        layout.show(MainPanel, "Display");
    }                                                   

    private javax.swing.JButton GoToDisplayPanelButton;                   
}

Answer 1

当数据发生变化时，您需要通过模型（＆＃34;后端＆＃34;）通知视图（GUI）来使用通知系统。然后视图可以请求更新的信息并使用它来更新JLabel显示。详细信息将取决于您的代码的具体情况，但我经常给我的模型（或模型周围的包装）一个SwingPropertyChangeSupport字段以及addPropertyChangeListener(...)和类似的删除侦听器方法，然后在模型＆更改属性的方法（绑定属性），触发SwingPropertyChangeSupport的通知方法。有关实现的更多详细信息，您应该考虑显示代码的一些详细信息，最好是minimal example program。

For example

修改

请注意，如果你想要的是关于何时调用show的通知，你可以随时扩展CardLayout并覆盖其show(...)方法。但是如果你这样做，也不要忘记调用super.show(...)方法。

修改
请注意对// !!

指示的代码所做的更改
import java.awt.CardLayout; import java.beans.PropertyChangeEvent; import java.beans.PropertyChangeListener; import javax.swing.*; @SuppressWarnings("serial") public class GUI extends javax.swing.JFrame { public static final String ITEM = "item"; public String item; // !! this should not be static! private javax.swing.JPanel MainPanel; public GUI() { // creates a JPanel called MainPanel which will hold the cards // in my CardLayout initComponents(); } // !! public void setItem(String item) { String oldValue = this.item; String newValue = item; this.item = item; firePropertyChange(ITEM, oldValue, newValue); } //!! public String getItem() { return item; } private void initComponents() { MainPanel = new javax.swing.JPanel(); setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); MainPanel.setBackground(new java.awt.Color(198, 118, 38)); MainPanel.setMaximumSize(new java.awt.Dimension(1000, 1000)); MainPanel.setName(""); // NOI18N MainPanel.setPreferredSize(new java.awt.Dimension(1024, 768)); MainPanel.setLayout(new java.awt.CardLayout()); javax.swing.GroupLayout layout = new javax.swing.GroupLayout( getContentPane()); getContentPane().setLayout(layout); layout.setHorizontalGroup(layout.createParallelGroup( javax.swing.GroupLayout.Alignment.LEADING).addGroup( javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup() .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) .addComponent(MainPanel, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addContainerGap())); layout.setVerticalGroup(layout.createParallelGroup( javax.swing.GroupLayout.Alignment.LEADING).addGroup( javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup() .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) .addComponent(MainPanel, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addContainerGap())); pack(); setLocationRelativeTo(null); } // Grab the panel that was created in initComponents() so that I can add // other panels to it public JPanel getMainPanel() { return MainPanel; } public static void main(String args[]) { java.awt.EventQueue.invokeLater(new Runnable() { @Override public void run() { final GUI mainGUI = new GUI(); // The JLabel in DisplayPanel.java will initially say root // !! item = "root"; mainGUI.setItem("root"); // !! JPanel cardHolder = mainGUI.getMainPanel(); // This panel contains a button which will update the name of // the currentUserAccount final MainMenuPanel mainMenu = new MainMenuPanel(cardHolder, mainGUI); // !! cardHolder.add(mainMenu, "MainMenu"); // This panel holds a JLabel that I want to have updated // automatically // when the user presses the button on MainMenuPanel final DisplayPanel display = new DisplayPanel(cardHolder, mainGUI); // !! cardHolder.add(display, "Display"); mainGUI.pack(); mainGUI.setVisible(true); // !! mainGUI.addPropertyChangeListener(ITEM, new PropertyChangeListener() { @Override public void propertyChange(PropertyChangeEvent pcEvt) { String itemText = mainGUI.getItem(); display.setJLabel1Text(itemText); } }); } }); } } @SuppressWarnings("serial") class DisplayPanel extends javax.swing.JPanel { private JPanel mainPanel; private GUI mainGui; // !! public DisplayPanel(JPanel mainPanel, GUI mainGui) { // !! this.mainPanel = mainPanel; this.mainGui = mainGui;// !! initComponents(); // Creates my panel with the JLabels/buttons etc } // !! added public void setJLabel1Text(String text) { jLabel1.setText(text); } private void initComponents() { jLabel1 = new javax.swing.JLabel(); GoToMainMenuButton = new javax.swing.JButton(); jLabel1.setFont(new java.awt.Font("Tahoma", 0, 18)); // NOI18N // !! jLabel1.setText(GUI.item); // sets the JLabel to the GUI.item // variable jLabel1.setText(mainGui.getItem()); // !! GoToMainMenuButton.setText("Go to MainMenuPanel"); GoToMainMenuButton.addMouseListener(new java.awt.event.MouseAdapter() { public void mouseClicked(java.awt.event.MouseEvent evt) { GoToMainMenuButtonMouseClicked(evt); } }); javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this); this.setLayout(layout); layout.setHorizontalGroup(layout .createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup( javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup() .addContainerGap(269, Short.MAX_VALUE) .addGroup( layout.createParallelGroup( javax.swing.GroupLayout.Alignment.LEADING) .addComponent(GoToMainMenuButton) .addComponent( jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 145, javax.swing.GroupLayout.PREFERRED_SIZE)) .addGap(266, 266, 266))); layout.setVerticalGroup(layout.createParallelGroup( javax.swing.GroupLayout.Alignment.LEADING).addGroup( layout.createSequentialGroup() .addGap(168, 168, 168) .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 63, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(83, 83, 83).addComponent(GoToMainMenuButton) .addContainerGap(116, Short.MAX_VALUE))); } private void GoToMainMenuButtonMouseClicked(java.awt.event.MouseEvent evt) { // go back to the MainPanel CardLayout layout = (CardLayout) (mainPanel.getLayout()); layout.show(mainPanel, "MainMenu"); } private javax.swing.JButton GoToMainMenuButton; private javax.swing.JLabel jLabel1; } @SuppressWarnings("serial") class MainMenuPanel extends javax.swing.JPanel { private JPanel MainPanel; private GUI mainGui; // !! public MainMenuPanel(JPanel MainPanel, GUI mainGui) { // !! this.MainPanel = MainPanel; this.mainGui = mainGui; // !! initComponents(); // Creates my panel with the JLabels/buttons etc } private void initComponents() { GoToDisplayPanelButton = new javax.swing.JButton(); GoToDisplayPanelButton.setText("Press Me"); GoToDisplayPanelButton .addMouseListener(new java.awt.event.MouseAdapter() { public void mouseClicked(java.awt.event.MouseEvent evt) { GoToDisplayPanelButtonMouseClicked(evt); } }); javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this); this.setLayout(layout); layout.setHorizontalGroup(layout.createParallelGroup( javax.swing.GroupLayout.Alignment.LEADING).addGroup( layout.createSequentialGroup().addGap(252, 252, 252) .addComponent(GoToDisplayPanelButton) .addContainerGap(260, Short.MAX_VALUE))); layout.setVerticalGroup(layout.createParallelGroup( javax.swing.GroupLayout.Alignment.LEADING).addGroup( javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup() .addContainerGap(198, Short.MAX_VALUE) .addComponent(GoToDisplayPanelButton).addGap(175, 175, 175))); } private void GoToDisplayPanelButtonMouseClicked(java.awt.event.MouseEvent evt) { // Changes the value of item. I want this change to be reflected on my // JLabel in DisplayPanel.java, but it is not because I do not explicitly // call setText on the JLabel here. I am wondering if there is a way to // have my JLabel automatically update when the variable in its setText // is changed, without having to directly call setText. Or some other // way to update it without calling setText every time I change something. // !! GUI.item = "new value"; mainGui.setItem("new value"); // !! // Switches to my DisplayPanel which should show the updated name in its // JLabel CardLayout layout = (CardLayout) (MainPanel.getLayout()); layout.show(MainPanel, "Display"); } private javax.swing.JButton GoToDisplayPanelButton; }

显示下一个面板时在CardLayout中更新JLables

1 个答案: