如何通过单击 JButton 添加 JPanel？

Posted 2023-02-26

【中文标题】如何通过单击 JButton 添加 JPanel？

【英文标题】：How to add JPanel by clicking JButton?

【发布时间】：2012-12-10 06:55:33

【问题描述】：

我正在尝试创建一个小型 GUI，它有 2 个 JButton 和 2 个 JPanel，每个都有一些绘图动画。默认情况下，它必须显示第一个 JPanel，通过单击第二个 JButton，我想查看我的第二个 JPanel。所以：我创建了 JFrame、Panel1 和 Panel2，在那里我绘制了我的动画，创建了 Button1 和 Button2 并向它们添加了 ActionListener。我还有 MainPanel，它在字段变量 i 中。通过更改此“i”，我的构造函数将 Panel1（默认）或 Panel2（通过单击 JButton2 我更改 i）添加到 MainPanel。比我将此 MainPanel 添加到我的框架中。所以我的问题是：在 MainPanel 类中我有 refreshMe 方法，我应该在那里写什么来使我的 GUI 正常工作？谢谢。这是我的代码：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class GuiTest 

    public static void main(String[] args) 
        JFrame f = new JFrame();
        MainPanel myPanel = new MainPanel();
        f.add(myPanel);
        Button1 button1 = new Button1();
        Button2 button2 = new Button2();
        myPanel.add(button1);
        myPanel.add(button2);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.pack();
        f.setVisible(true);
    


class MainPanel extends JPanel 
    Panel1 p1 = new Panel1();
    Panel2 p2 = new Panel2();
    public int i = 1;  //this is being changed later by clicking JButton
    // I use this setter later in actionPerformed in order to change i
    public void setI(int i) 
        this.i = i;
    

    MainPanel()  
        if (i == 1) 
            this.add(p1);
        
        if (i == 2) 
            this.add(p2);
        
    

    public void refreshMe() 
        // Need some help here:
        // I don't know what should I write, how to make a repaint of myPanel?
        System.out.println("just test, if the method refreshMe working by clicking some button");
    


class Panel1 extends JPanel 

    public Panel1() 
        this.setBackground(Color.BLUE);
        // a lot of drawing stuff going on here
    

    @Override
    public Dimension getPreferredSize() 
        return new Dimension(200, 200);
    


class Panel2 extends JPanel 

    public Panel2() 
        this.setBackground(Color.GREEN);
        // a lot of drawing stuff going on here
    

    @Override
    public Dimension getPreferredSize() 
        return new Dimension(200, 200);
    



class Button1 extends JButton 
    MainPanel someObj1 = new MainPanel();

    Button1() 
        setText("Show Annimation A");
        addActionListener(new ActionListener() 

            @Override
            public void actionPerformed(ActionEvent e) 
                someObj1.setI(1);
                System.out.println("The variable i is now: " + someObj1.i);
                someObj1.refreshMe();

            
        );
    



class Button2 extends JButton 
    MainPanel someObj2 = new MainPanel();

    Button2() 
        setText("Show Annimation B");
        addActionListener(new ActionListener() 

            @Override
            public void actionPerformed(ActionEvent e) 
                someObj2.setI(2);
                System.out.println("The variable i is now: " + someObj2.i);
                someObj2.refreshMe();
            
        );

    

【参考方案1】：

为了在添加/删除或调整可见容器上的组件后反映更改，在添加/删除或调整组件大小后，在容器实例上调用 revalidate() 和 repaint()。

虽然这在您的代码中不起作用，但主要原因是在 JButton 类中，您重新创建 MainPanel 的新实例，而实际上 2 JButtons 应该共享正在使用的单个实例（您可以传递 MainPanel 实例到JButtons 构造函数，但你不应该真正扩展JButton，除非添加自定义功能）：

class Button2 extends JButton 
    MainPanel someObj2 = new MainPanel();//you create an instance of MainPanel which isnt even showing and than do changes on that, this way you will never see any of the changes

    Button2() 
    

关于您的代码的其他一些建议：

不要不必要地扩展 JButton 类，只需像使用 JFrame 一样创建 JButton 的实例并调用 JButton 实例上的方法。

别忘了在Event Dispatch Thread 上创建/操作Swing 组件，通过SwingUtilities.invokeLater(..) 块，阅读here 了解更多信息。

这是您的代码已修复（上述建议等已实施）：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Test 

    public static void main(String[] args) 
        SwingUtilities.invokeLater(new Runnable() 
            @Override
            public void run() 
                JFrame f = new JFrame();

                final MainPanel myPanel = new MainPanel();
                f.add(myPanel);

                JButton button1 = new JButton("Show Animation A");
                JButton button2 = new JButton("Show Animation B");

                button1.addActionListener(new ActionListener() 
                    @Override
                    public void actionPerformed(ActionEvent e) 
                        myPanel.setI(1);
                        System.out.println("The variable i is now: " + myPanel.i);
                        myPanel.refreshMe();
                    
                );
                button2.addActionListener(new ActionListener() 
                    @Override
                    public void actionPerformed(ActionEvent e) 
                        myPanel.setI(2);
                        System.out.println("The variable i is now: " + myPanel.i);
                        myPanel.refreshMe();
                    
                );

                myPanel.add(button1);
                myPanel.add(button2);
                myPanel.checkPanel();

                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

                f.pack();
                f.setVisible(true);
            
        );
    


class MainPanel extends JPanel 

    Panel1 p1 = new Panel1();
    Panel2 p2 = new Panel2();
    public int i = 1;  //this is being changed later by clicking JButton
    // I use this setter later in actionPerformed in order to change i

    public void setI(int i) 
        this.i = i;
    

    public void refreshMe() 
        checkPanel();

        revalidate();
        repaint();
        // Need some help here:
        // I don't know what should I write, how to make a repaint of myPanel?
        System.out.println("just test, if the method refreshMe working by clicking some button");
    

    public void checkPanel() 
        if (i == 1) 
            this.add(p1);
            this.remove(p2);//or it will remain there as this is default flowlayout
         else if (i == 2) 
            this.add(p2);
            this.remove(p1);
        
    


class Panel1 extends JPanel 

    public Panel1() 
        this.setBackground(Color.BLUE);
        // a lot of drawing stuff going on here
    

    @Override
    public Dimension getPreferredSize() 
        return new Dimension(200, 200);
    


class Panel2 extends JPanel 

    public Panel2() 
        this.setBackground(Color.GREEN);
        // a lot of drawing stuff going on here
    

    @Override
    public Dimension getPreferredSize() 
        return new Dimension(200, 200);
    

不过我建议一些更简单的东西，幸运的是你有 2 个选择：

1) 使用CardLayout，这将允许您在单个JFrame/container 上的多个组件之间切换。

这是我做的一个例子：

import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Test 

    private final static String PANEL1 = "panel 1";
    private final static String PANEL2 = "panel 2";

    public Test() 
        initComponents();
    

    public static void main(String[] args) 
        SwingUtilities.invokeLater(new Runnable() 
            @Override
            public void run() 
                new Test();
            
        );
    

    private void initComponents() 
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panel1 = new JPanel();
        panel1.add(new JLabel("Panel 1"));

        JPanel panel2 = new JPanel();
        panel2.add(new JLabel("Panel 2"));

        //Create the panel that contains the "cards".
        final JPanel cards = new JPanel(new CardLayout());
        cards.add(panel1, PANEL1);
        cards.add(panel2, PANEL2);

        //create button to allow chnage to next card
        JButton buttonNext = new JButton(">");
        buttonNext.addActionListener(new ActionListener() 
            @Override
            public void actionPerformed(ActionEvent ae) 
                CardLayout cl = (CardLayout) (cards.getLayout());//get cards
                cl.next(cards);
            
        );

        //create button to allow chnage to previous card
        JButton buttonPrev = new JButton("<");
        buttonPrev.addActionListener(new ActionListener() 
            @Override
            public void actionPerformed(ActionEvent ae) 
                CardLayout cl = (CardLayout) (cards.getLayout());//get cards
                cl.previous(cards);
            
        );

        //create panel to hold buttons which will allow switching between cards
        JPanel buttonPanel = new JPanel();
        buttonPanel.add(buttonPrev);
        buttonPanel.add(buttonNext);


        frame.add(cards);
        frame.add(buttonPanel, BorderLayout.SOUTH);

        frame.pack();
        frame.setVisible(true);
    

2) 使用removeAll() 技术，即调用frame.getContentPane().removeAll()，这将删除当前在JFrame 上的所有组件，然后添加新内容并调用revalidate() 和repaint()（也可能要添加pack() in那里）在JFrame 实例上以反映更改。虽然我推荐CardLayout。

【讨论】：

感谢您更正我的代码和示例，这很有帮助！是的，CardLayout 解决了我的问题。

【参考方案2】：

我认为您可以使用CardLayout 来实现您的功能。请参考here