如何通过点击JButton添加JPanel？

Question

我正在尝试创建一个小型GUI，它有2个JButton和2个JPanels，每个JPanels上都有一些绘图动画。默认情况下，它必须显示第一个JPanel，并通过单击第二个JButton来查看我的第二个JPanel。所以：我创建了JFrame、Panel1和Panel2，在其中绘制了我的动画，创建了Button1和Button2，并向它们添加了ActionListeners。我还有一个MainPanel，它在一个字段变量i中。通过更改这个"i"，我的构造函数将Panel1（默认）或Panel2（通过单击JButton2来更改i）添加到MainPanel中。然后我将此MainPanel添加到我的frame中。所以我的问题是：在MainPanel类中，我有一个refreshMe方法，我应该在那里写什么才能使我的GUI正常工作？谢谢。以下是我的代码：

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();
            }
        });

    }

}

- user1924939

Answer 1

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

尽管这不会在您的代码中起作用，主要原因是在JButton类内部重新创建了一个新的MainPanel实例，而实际上2个JButtons应该共享正在使用的单个实例（您可以将MainPanel实例传递给JButton构造函数，但是除非添加自定义功能，否则不应扩展JButton）。

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，以下是一些建议：

• 不要不必要地扩展JButton类，只需像使用JFrame一样创建JButton实例，并在JButton实例上调用方法。

• 不要忘记在Event Dispatch Thread上创建/操作Swing组件，通过SwingUtilities.invokeLater(..)块，点击此处了解更多信息。

这是您修复后的代码（实现了上述建议等）：

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);
    }
}

我建议您使用更简单的方法，幸运的是您有两个选择：

1）使用CardLayout，这样可以在单个JFrame/容器中的多个组件之间进行翻转。

以下是我制作的示例：

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()，将删除当前在 JFrame 上的所有组件，然后添加新内容并在 JFrame 实例上调用 revalidate() 和 repaint()（也可能需要添加 pack()）以反映更改。虽然我建议使用 CardLayout。

- David Kroukamp

---

谢谢您纠正我的代码和示例，这对我帮助很大！是的，CardLayout解决了我的问题。 - user1924939

Answer 2

我认为您可以使用CardLayout来实现您的功能。请参考这里。

- Weibo