جافا سوينغ - Jslider و Jcombobox تسبب أخطاء وقت التشغيل

Question

حسنا، سأقوم بنشر الرمز للفصول الثلاثة لأنها ليست طويلة جدا.

package guiDemonstration;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class TabbedGUI {
    //create fields
    private JFrame frame;
    private JTabbedPane tabbedPane;

    //make the following three labels public for access in the GUIEngine class
    private JLabel comboLabel; 
    private JLabel sliderLabel; 
    private JLabel radioLabel; 
    private JSlider slider;
    private JComboBox combo;
    private JPanel comboPanel, sliderPanel, radioPanel;
    private String []comboArray;
    private JRadioButton radio, radio1, radio2;
    private ButtonGroup buttonGroup;

    private String comboText = "Please Make a Choice";
    private String sliderText = "Move the Slider";
    private String radioText = "Choose a Radio Button";

    //Create field to hold GUIEngine Class
    GUIEngine engine;

    // empty constructor
    public TabbedGUI(){
    }

    //method used to construct the gui
    private void makeFrame(){
        //create the Frame
        frame = new JFrame("Example of a Tabbed GUI");

        //set the initial size of the frame in pixels
        frame.setSize(500, 200);
        //add the frame to the contentPane
        Container contentPane = frame.getContentPane();

        //create an instance of the GUIEngine class
        engine = new GUIEngine();

       //create an array of size 3 to be used as dropdown values in the combobox
        comboArray = new String[3];

        //initialise the array
        comboArray[0] = "First Choice";
        comboArray[1] = "Second Choice";
        comboArray[2] = "Third Choice";

        //create instance of JComboBox and add array
        combo = new JComboBox(comboArray);

        //create instance of JSlider
        slider = new JSlider();

        //creat instance of Button Group
        // this ButtonGroup will hold the individual radio buttons
        buttonGroup = new ButtonGroup();

        radio = new JRadioButton();
        radio1 = new JRadioButton();
        radio2 = new JRadioButton();

        //create instances of JPanel
        comboPanel = new JPanel();
        sliderPanel= new JPanel();
        radioPanel = new JPanel();

        //create flowlayout for comboPanel
        comboPanel.setLayout(new FlowLayout());

        //create instances of labels
        comboLabel = new JLabel(comboText);
        sliderLabel=new JLabel(sliderText);
        radioLabel = new JLabel(radioText);

        //add radio buttons to the group
        buttonGroup.add(radio);
        buttonGroup.add(radio1);
        buttonGroup.add(radio2);

        //add a border to the button group


        //begin creation of the tabbed GUI and add to contentPane
        tabbedPane = new JTabbedPane();
        contentPane.add(tabbedPane);

        frame.add(tabbedPane);

        //add instances of JPanel to each tab
        tabbedPane.addTab("Combo Box", comboPanel);
        tabbedPane.addTab("Slider", sliderPanel);
        tabbedPane.addTab("Radio", radioPanel);

        //add components to each JPanel of each tab
        comboPanel.add(combo);
        comboPanel.add(comboLabel);
        sliderPanel.add(sliderLabel);
        radioPanel.add(radioLabel);
        sliderPanel.add(slider);
        radioPanel.add(radio);
        radioPanel.add(radio1);
        radioPanel.add(radio2);

        //set a border around the Slider
        slider.setBorder(
                BorderFactory.createMatteBorder(1, 1, 1, 1, Color.BLUE));

        // call the method to add the listeners to each component
        addListeners();

        //by default the frame is set to invisible. Set the frame to visible
        frame.setVisible(true);
    }

    /**
     * This method adds listeners to each component
     */
    public void addListeners(){

        //add actionListeners to each component

        combo.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
                engine.useCombo();
            }
        });

        slider.addChangeListener(new ChangeListener(){
            public void stateChanged(ChangeEvent e){
                engine.useSlider();
            }
        });

        radio.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
                engine.useRadioButtons();
            }
        });

        radio1.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
                engine.useRadioButtons();
            }
        });

        radio2.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
                engine.useRadioButtons();
            }
        });
    }

    /*
     * The following three methods set the text for each
     * label on the three individual tabs.
     * These methods are called from the GUIEngine Class.
     */

    //set the text on the comboLabel
    public void setComboLabel(){
        String updatedComboText = (String)combo.getSelectedItem();
        comboLabel.setText(updatedComboText);
        //System.out.println("You selected" + comboText);
    }

    //set the text on the sliderLabel
    public void setSliderLabel(){
        sliderLabel.setText("You've moved the slider!");
    }

    //set the text on the radioLabel
    public void setRadioLabel(){
        System.out.println("You've selected a radio button!");
    }

    /**
     * This method is used to begin execution of the program
     */
    public void runProgram(){
        makeFrame();
    }
}

الصف 2:

package guiDemonstration;

public class GUIEngine {

    TabbedGUI tg;

    //constructor
    public GUIEngine(){
        tg = new TabbedGUI();
    }

    public void useCombo(){
        //System.out.println("You Used the Combo Box");
        tg.setComboLabel();
    }

    public void useSlider(){
        tg.setSliderLabel();
    }

    public void useRadioButtons(){
        //System.out.println("You clicked a radio button");
        tg.setRadioLabel();
    }
}

والطريقة الرئيسية فقط:

package guiDemonstration;

public class Controller {
    /**
     * #This is the main method where program execution begins
     * @param args
     */
    public static void main(String[] args) {
        TabbedGUI tg = new TabbedGUI();
        tg.runProgram();
    }
}

JCOMBOBOX و JSLIDER يسبب أخطاء وقت التشغيل. يعتبر الرمز موافق، ولكن عندما أقوم بنقل JSLider أو حدد عنصر في JCombobox، تعطل البرنامج.

أيه أفكار؟

فرنك غيني

Answer 1

يقوم JuiEngine بإنشاء مثيل خاص به من tabbedgui بدلا من استخدام المثيل الذي تنشئه في الأسلوب الرئيسي الخاص بك.

إذا كنت بحاجة إلى الحفاظ على فئة الجيونغين حولها، فسوف أقترح القيام بذلك في المقدمة

المحرك = جويلنغين جديد (هذا)؛

ثم قم بتغيير منشئ GuiEngine لاتخاذ في tabbedgui كمعلمة. قد تجعل مثيل النهائي المتغير أيضا.

Answer 2

sliderLabel.setText("You've moved the slider!");

التي تسبب nullpointerexception مما يعني أنه لم يتم إنشاء SliderLabel بعد. تأكد من أن تفعل:

sliderLabel = new JLabel()

قبل الدعوة إلى seatsliderlabel