java - 对多个 JPanel 使用 CardLayout 并且不显示任何内容

Question

我正在制作一个简单(且虚假)的计算机功耗计算器。我使用卡片布局来放置多个面板，但是当我运行它时，只有一个小窗口不显示任何内容。这是我的长代码，我将它们全部放在一个类中。

package my.Project;

import java.awt.*;
import java.awt.event.*;
import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.text.DecimalFormat;
import javax.swing.*;


public class MainProject extends JFrame {

CardLayout cl;

int motherboardP, oddP, hddP, ssdP, fanP, cpuP, gpuP, monitorP, hoursint;
int ramNum, hddNum, ssdNum, fanNum, gpuNum;
double ramP, totalP, powerPerYear;
public float tariff = (float) 0.2180;
public float costRM;

JPanel mainPage, secondPage, thirdPage, results;
//JPanel panelCont;
JLabel title, icon, motherboard, ram, numram,
        numssd, numhdd, odd, numfan, cpu, gpu,
        numgpu, monitor, hours, outage, peryear,
        costyear, watt, kwatt, rm;

JButton start, exit1, exit2, nxt1, bck1, nxt2, bck2, done, bck3, tips, calc;

JTextField numRam, numSSD, numHDD, numFan, numGpu, hoursUse,
        outagePC, perYear, cost;

JComboBox mboardBox, ramBox, oddBox, cpuBox, gpuBox,
        monitorBox;

public MainProject() {
    initComponents();
}

public void initComponents() {

    setTitle("Power Consumption Calculator");
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setSize(500, 400);

    Container contentPane = getContentPane();

    contentPane.setLayout(cl);

    /*
    panelCont = new JPanel();
    cl = new CardLayout();
    */

    //contentPane.add(panelCont);

    /*
    panelCont.setLayout(cl);
    panelCont.add(mainPage,"1");
    panelCont.add(secondPage,"2");
    panelCont.add(thirdPage,"3");
    panelCont.add(results,"4");
    cl.show(panelCont,"1");
    */

    mainPage = new JPanel();

    secondPage = new JPanel();

    thirdPage = new JPanel();

    results = new JPanel();

    cl.show(contentPane,"1");

    contentPane.add("1", mainPage);
    contentPane.add("2", secondPage);
    contentPane.add("3", thirdPage);
    contentPane.add("4", results);

    title.setFont(new Font("Tahoma", Font.BOLD, 18));
    title.setText("Computer Power Consumption Calculator");
    motherboard.setText("Motherboard:");
    ram.setText("RAM:");
    numram.setText("No. of RAM Sticks:");
    numssd.setText("Num. of SSD:");
    numhdd.setText("Num. of HDD:");
    odd.setText("Optical Disk Drive:");
    numfan.setText("Num. of Fans:");
    cpu.setText("CPU:");
    gpu.setText("GPU:");
    numgpu.setText("Num. of GPU:");
    monitor.setText("Monitor:");
    hours.setText("Hours of usage/day:");
    outage.setText("PC Power Outage:");
    peryear.setText("Per year:");
    costyear.setText("Cost/year");
    watt.setText("Watts (W)");
    kwatt.setText("kiloWatts(kW)");
    rm.setText("RM");

    icon.setIcon(new javax.swing.ImageIcon(getClass().getResource("/my/Project/pclogo.png")));

    BorderLayout mainL = new BorderLayout();
    mainPage.setLayout(mainL);
    mainPage.add(title, BorderLayout.PAGE_START);
    mainPage.add(icon, BorderLayout.CENTER);
    mainPage.add(start, BorderLayout.SOUTH);
    mainPage.add(exit1,BorderLayout.SOUTH);

    GridLayout secondL = new GridLayout(0,2);
    secondPage.setLayout(secondL);
    secondPage.add(motherboard);
    secondPage.add(mboardBox);
    secondPage.add(ram);
    secondPage.add(ramBox);
    secondPage.add(numram);
    secondPage.add(numRam);
    secondPage.add(numssd);
    secondPage.add(numSSD);
    secondPage.add(numhdd);
    secondPage.add(numHDD);
    secondPage.add(odd);
    secondPage.add(oddBox);
    secondPage.add(numfan);
    secondPage.add(numFan);
    secondPage.add(nxt1);
    secondPage.add(bck1);

    GridLayout thirdL = new GridLayout(0,2);
    thirdPage.setLayout(thirdL);
    thirdPage.add(cpu);
    thirdPage.add(cpuBox);
    thirdPage.add(gpu);
    thirdPage.add(gpuBox);
    thirdPage.add(numGpu);
    thirdPage.add(monitor);
    thirdPage.add(monitorBox);
    thirdPage.add(hours);
    thirdPage.add(hoursUse);
    thirdPage.add(nxt2);
    thirdPage.add(bck2);

    GridLayout resultL = new GridLayout(0,3);
    results.setLayout(resultL);
    results.add(outage);
    results.add(outagePC);
    results.add(watt);
    results.add(peryear);
    results.add(perYear);
    results.add(kwatt);
    results.add(costyear);
    results.add(cost);
    results.add(rm);
    results.add(calc);
    results.add(bck3);
    results.add(exit2);
    results.add(tips);

    start.setText("Start");
    start.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            //startActionPerformed(evt);
            cl.show(contentPane,"2");
        }
    });

    exit1.setText("Exit");
    exit1.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
           // exit1ActionPerformed(evt);
            System.exit(0);
        }
    });

    exit2.setText("Exit");
    exit2.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
           // exit2ActionPerformed(evt);
            System.exit(0);
        }
    });

    nxt1.setText("Next >>");
    nxt1.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
          //  nxt1ActionPerformed(evt);
            cl.show(contentPane,"3");
            ramNum = Integer.parseInt(numRam.getText());
            ssdNum = Integer.parseInt(numSSD.getText());
            hddNum = Integer.parseInt(numHDD.getText());
            fanNum = Integer.parseInt(numFan.getText());

            JComboBox cb1 = (JComboBox)evt.getSource();
            String mboard = (String)cb1.getSelectedItem();
            if("Average".equals(mboard)) {
              motherboardP = 32;
            }
            if("High End".equals(mboard)) {
              motherboardP = 60;
            }

            JComboBox cb2 = (JComboBox)evt.getSource();
            String ramType = (String)cb2.getSelectedItem();
            if("DDDR1".equals(ramType)) {
                ramP = 5;
            }
            if("DDR2".equals(ramType)) {
                ramP = 4;
            }
            if("DDR3".equals(ramType)) {
                ramP = 2.5;
            }

            JComboBox cb3 = (JComboBox)evt.getSource();
            String typeODD = (String)cb3.getSelectedItem();
            if("DVD".equals(typeODD)) {
                oddP = 22;
            }
            if("BluRay".equals(typeODD)) {
                oddP = 27;
            }


        }
    });

    nxt2.setText("Next >>");
    nxt2.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
           // nxt2ActionPerformed(evt);
            cl.show(contentPane,"4");

            gpuNum = Integer.parseInt(numGpu.getText());
            hoursint = Integer.parseInt(hoursUse.getText());

            JComboBox cb4 = (JComboBox)evt.getSource();
            int inCPU = (Integer)cb4.getSelectedIndex();
            switch(inCPU) {
                case 0:
                    cpuP = 89;
                    break;
                case 1:
                    cpuP = 119;
                    break;
                case 2:
                    cpuP = 127;
                    break;
                case 3:
                    cpuP = 125;
                    break;
                case 4:
                    cpuP = 33;
                    break;
                case 5:
                    cpuP = 98;
                    break;

            }

            JComboBox cb5 = (JComboBox)evt.getSource();
            int nvGPU = (Integer)cb5.getSelectedIndex();

            switch(nvGPU) {
                case 0:
                    gpuP = 295;
                    break;
                case 1:
                    gpuP = 100;
                    break;
                case 2:
                    gpuP = 250;
                    break;
                case 3:
                    gpuP = 150;
                    break;
                case 4:
                    gpuP = 105;
                    break;
                case 5:
                    gpuP = 275;
                    break;
            }

            JComboBox cb6 = (JComboBox)evt.getSource();
            int mSize = (Integer)cb6.getSelectedIndex();
            if(mSize == 0) {
                monitorP = 20;
            }
            if(mSize == 1) {
                monitorP = 28;
            }
            if(mSize == 2) {
                monitorP = 50;
            }

        }
    });

    bck1.setText("<< Back");
    bck1.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
           // bck1ActionPerformed(evt);
            cl.show(contentPane,"1");
        }
    });

    bck2.setText("<< Back");
    bck2.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
          //  bck2ActionPerformed(evt);
            cl.show(contentPane,"2");
        }
    });

    bck3.setText("<< Back");
    bck3.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
           // bck3ActionPerformed(evt);
            cl.show(contentPane,"3");
        }
    });

    tips.setText("Tips on saving energy");
    tips.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            //tipsActionPerformed(evt);
            try {

        String url ="http://www.toptenreviews.com/computers/articles/10-computer-energy-saving-tips-go-green/";

        Desktop dt = Desktop.getDesktop();
        URI uri = new URI(url);
        dt.browse(uri.resolve(uri));
    }    

    catch (URISyntaxException | IOException e) {
        JOptionPane.showMessageDialog(null, e.getMessage());
    }
        }
    });

    calc.setText("Calculate");
    calc.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
           // calcActionPerformed(evt);

            gpuP *= gpuNum;
            ramP *= ramNum;
            hddP = hddNum * 5;
            ssdP = ssdNum * 3;
            fanP = fanNum * 4;

            totalP = motherboardP + cpuP + gpuP + ramP +
            hddP + ssdP + monitorP + fanP;
            powerPerYear = totalP * hoursint * 365;

            costRM = (float) ((powerPerYear / 1000) * tariff);

            DecimalFormat df = new DecimalFormat("#.##");
            df.format(costRM);

            String outage = Double.toString(totalP);
            String ppy = Double.toString(powerPerYear);
            String price = Float.toString(costRM);

            outagePC.setText(outage);
            perYear.setText(ppy);
            cost.setText(price);
        }
    });

    mboardBox.setModel(new DefaultComboBoxModel(new String[] { "Average", "High End" }));
    mboardBox.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
           // mboardBoxActionPerformed(evt);
            JComboBox cb = (JComboBox)evt.getSource();
            String mboard = (String)cb.getSelectedItem();
            if("Average".equals(mboard)) {
              motherboardP = 32;
            }
            if("High End".equals(mboard)) {
              motherboardP = 60;
            }
        }
    });

    ramBox.setModel(new DefaultComboBoxModel(new String[] { "DDR1", "DDR2", "DDR3" }));
    ramBox.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            //ramBoxActionPerformed(evt);
            JComboBox cb = (JComboBox)evt.getSource();
            String ramType = (String)cb.getSelectedItem();
            if("DDDR1".equals(ramType)) {
                ramP = 5;
            }
            if("DDR2".equals(ramType)) {
                ramP = 4;
            }
            if("DDR3".equals(ramType)) {
                ramP = 2.5;
            }
        }
    });

    oddBox.setModel(new DefaultComboBoxModel(new String[] { "DVD", "BluRay" }));
    oddBox.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            //oddBoxActionPerformed(evt);
            JComboBox cb = (JComboBox)evt.getSource();
            String typeODD = (String)cb.getSelectedItem();
            if("DVD".equals(typeODD)) {
                oddP = 22;
            }
            if("BluRay".equals(typeODD)) {
                oddP = 27;
            }
        }
    });

    cpuBox.setModel(new DefaultComboBoxModel(new String[] { "intel Core i3", "intel Core i5", "intel Core i7", "AMD FX 4350", "AMD Sempron 64 3500", "AMD Athlon 64 FX-62" }));
    cpuBox.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            //cpuBoxActionPerformed(evt);
            JComboBox cb = (JComboBox)evt.getSource();
            int inCPU = (Integer)cb.getSelectedIndex();
            switch(inCPU) {
                case 0:
                    cpuP = 89;
                    break;
                case 1:
                    cpuP = 119;
                    break;
                case 2:
                    cpuP = 127;
                    break;
                case 3:
                    cpuP = 125;
                    break;
                case 4:
                    cpuP = 33;
                    break;
                case 5:
                    cpuP = 98;
                    break;

            }

        }
    });

    gpuBox.setModel(new DefaultComboBoxModel(new String[] { "NVidia GTX 500", "NVidia GTX 700", "NVidia GTX Titan", "AMD Radeon HD 2900", "AMD Radeon HD 3870", "AMD Radeon R9 Fury X" }));
    gpuBox.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            //gpuBoxActionPerformed(evt);
            JComboBox cb = (JComboBox)evt.getSource();
            int nvGPU = (Integer)cb.getSelectedIndex();

            switch(nvGPU) {
                case 0:
                    gpuP = 295;
                    break;
                case 1:
                    gpuP = 100;
                    break;
                case 2:
                    gpuP = 250;
                    break;
                case 3:
                    gpuP = 150;
                    break;
                case 4:
                    gpuP = 105;
                    break;
                case 5:
                    gpuP = 275;
                    break;
            }
        }

    });

    monitorBox.setModel(new DefaultComboBoxModel(new String[] { "17\"-19\"", "20\"-22\"", "24\"-30\"" }));
    monitorBox.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            //monitorBoxActionPerformed(evt);
            JComboBox cb = (JComboBox)evt.getSource();
            int mSize = (Integer)cb.getSelectedIndex();
            if(mSize == 0) {
                monitorP = 20;
            }
            if(mSize == 1) {
                monitorP = 28;
            }
            if(mSize == 2) {
                monitorP = 50;
            }
        }

    });


}

public static void go() {

    JFrame frame = new JFrame();
    frame.setVisible(true);
}

public static void main(String[] args) {

    MainProject.go();

}

}

我应该在哪里修复代码以及我的代码中实现了多少错误的 Java 编程实践？

Answer 1

首先...

在将 CardLayout 应用到容器之前以及添加任何组件之前，您需要创建一个 CardLayout 实例...

    cl = new CardLayout();
    contentPane.setLayout(cl);

第二...

您应该使用add(Component, Object)方法

contentPane.add(mainPage, "1");

第三

public static void go() {

    JFrame frame = new JFrame();
    frame.setVisible(true);
}

什么也不做，只是创建一个空的框架，里面什么也没有。实际使用 MainProject 可能会有所帮助，因为它扩展自 JFrame

第四...

不要直接从 JFrame 扩展，您不会向类添加任何新功能，它会将您锁定在单一用例中，并会导致像您所遇到的问题。

相反，请考虑从 JPanel 开始......

public class MainProject extends JPanel {

(ps-此更改可能会导致其他编译器错误，我不会在此处尝试修复这些错误)

然后简单地创建一个 JFrame 的新实例并向其中添加您的组件...

public static void go() {
    EventQueue.invokeLater(new Runnable() {
        @Override
        public void run() {
            try {
                UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
            } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                ex.printStackTrace();
            }

            JFrame frame = new JFrame("Testing");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.add(new MainProject());
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        }
    });
}

第五

您可能想仔细看看...

• Creating a GUI With JFC/Swing
• How to Use CardLayout

还有...

• Why is my JLabel not showing up
• Listener Placement Adhering to the Traditional (non-mediator) MVC Pattern

了解更多想法以及如何更好地管理 CardLayout

您可能还想查看How to Use Tabbed Panes替代方案