当 JPanel 发生变化时，旧 JPanel 的元素会被留下

Question

我正在使用 JTabbedPane，每个选项卡上都有一个面板，当用户执行诸如单击按钮之类的操作时，该面板会发生变化。我遇到的问题是上一个面板中的元素被遗忘了。通常在将鼠标移到它们上之前您是看不到它们的，但有时在将鼠标移到它们应该的位置之前，您看不到 new 面板的元素是。所以很多时候一开始只有一点点可见，然后：

when you run your mouse over more stuff it becomes visible

Then for some reason when you hit 'multiple choice', which is supposed to create the four new buttons, everything becomes perfectly visible.

repaint(); 几乎与其他所有行一样，在我更改 GUI 上的任何内容之前，我先执行removeAll();，但一切都会回来！有什么建议么？此面板的代码如下，如果它可能有帮助...

package com.GC01.gui;

import java.awt.Color;

public class PracticeQuizPanel extends JPanel implements MouseListener {
    /**
     * This panel will allow the user to practice quiz questions.
     */
private static final long serialVersionUID = 1L;

private User user = new User("misha");

boolean isMultipleChoice=false;
boolean usedClue=false;
boolean isStarted=false;

Calendar calendar = Calendar.getInstance();
AnswerAnalysis aA = new AnswerAnalysis();   
private Quiz qz = new Quiz( Quiz.getQuestionsFromDisk(), 4, TabbedQuiz.getUser().getNumLogins() );

private JTextArea questionArea;
private JTextArea clueArea;
private JTextArea answerArea;

private JButton clueButton;
private JButton multiButton;
private JButton answerButton;
private JButton startButton; 

private int index=0;
private Calendar startCalendar, endCalendar;

private JPanel backPanel;

public PracticeQuizPanel(){
    add(new StartButtonPanel());
}

PracticeQuizPanel(int index) {
    createVisualElements(index);
}

public void offerAnswer(){
    endCalendar = Calendar.getInstance();
    aA.setTimeSpent((int) (endCalendar.getTimeInMillis()-startCalendar.getTimeInMillis()));
    aA.setRight(answerArea.getText());
    JOptionPane.showMessageDialog(null, aA.toString());
    answerArea.setEditable(false);
    qz.setAnswersAnalysis(index, aA);
    index++;
    removeAll(); 
    if( index<qz.getLength() ) createVisualElements(index);
    else {
        removeAll();
        JOptionPane.showMessageDialog(null, qz.toFriendlyString());
        addQuizResultsToUserProgress();
        JOptionPane.showMessageDialog(null, qz.toFriendlyString());
        UserProgress uP = new UserProgress(user);
        System.out.println(uP.toString());
    }
    repaint();
    startCalendar = Calendar.getInstance();
    //JOptionPane.showMessageDialog(null, isStarted);
}

public void addQuizResultsToUserProgress(){
    UserProgress userProgress = new UserProgress(user);
    ArrayList<AnswerAnalysis> asA = userProgress.getAnswersAnalysis();
    for (int i=0; i<qz.getLength(); i++){
        asA.add( qz.getAnswersAnalysis()[i]);
    }
    userProgress.setAnswersAnalysis(asA);
    userProgress.saveProgress();
}



/**
 * This method creates/recreates all the text boxes, buttons etc. without resetting the quiz and
 * the objects in memory.
 */
private void createVisualElements(int index){
    if (TabbedQuiz.getUser().getNumLogins()<0) 
        JOptionPane.showMessageDialog(null, "There was an error. You may have done this quiz before.");
    removeAll();
    repaint();
    startCalendar = Calendar.getInstance();
    this.index=index;
    setBackground(new Color(112, 128, 144)); 
    setBounds(0,0,728,380);
    setLayout(null);

    questionArea = new JTextArea();
    questionArea.setFont(TabbedQuiz.getDefaultFont().deriveFont(20));//new Font("Courier New", 0, 20));
    questionArea.setEditable(false);
    questionArea.setLineWrap(true);
    questionArea.setWrapStyleWord(true);
    questionArea.setBounds(295, 11, 423, 74);
    add(questionArea);
    //int index=0;
    Question q = qz.getQuestions().get(index);
    aA = new AnswerAnalysis(q.getQuestionID());
    questionArea.setText(q.getQuestionText() );

    clueArea = new JTextArea();
    clueArea.setFont(TabbedQuiz.getDefaultFont().deriveFont(20));
    clueArea.setEditable(false);
    clueArea.setLineWrap(true);
    clueArea.setWrapStyleWord(true);
    clueArea.setBounds(295, 104, 423, 55);
    add(clueArea);

    JLabel lblQuestion = new JLabel("QUESTION:");
    lblQuestion.setFont(TabbedQuiz.getDefaultFont().deriveFont(40));
    lblQuestion.setBounds(43, 11, 216, 61);
    add(lblQuestion);

    answerArea = new JTextArea();//index+"");
    answerArea.setFont(TabbedQuiz.getDefaultFont().deriveFont(20));
    answerArea.setLineWrap(true);
    answerArea.setWrapStyleWord(true);
    answerArea.setBounds(295, 301, 423, 50);
    answerArea.addKeyListener(new KeyAdapter() {
        @Override
        public void keyPressed(KeyEvent e) {
            if(e.getKeyCode() == KeyEvent.VK_ENTER) offerAnswer();
        }
    });

    add(answerArea);
    answerArea.setFocusable(true);
    answerArea.requestFocusInWindow();

    clueButton = new JButton("CLUE?");
    clueButton.setFont(TabbedQuiz.getDefaultFont().deriveFont(40));
    clueButton.addMouseListener(this);
    clueButton.setBounds(15, 104, 244, 55);
    add(clueButton);

    multiButton = new JButton("MULTIPLE CHOICE?");
    multiButton.setFont(TabbedQuiz.getDefaultFont().deriveFont(20));
    multiButton.addMouseListener(this);
    multiButton.setBounds(15, 195, 244, 55);
    add(multiButton);

    answerButton = new JButton("ANSWER!");
    answerButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {
        }
    });
    answerButton.setFont(TabbedQuiz.getDefaultFont().deriveFont(40));
    answerButton.setBounds(15, 301, 244, 55);
    answerButton.addMouseListener(this);
    add(answerButton);

    backPanel = new JPanel();
    backPanel.setBounds(0, 0, 728, 380);
    //add(backPanel);

    this.setVisible(true);
    repaint();
}

@Override
public void mouseClicked(MouseEvent e) {
    if      ( e.getSource().equals(startButton)  ) {
        remove(startButton); repaint(); isStarted=true;
        startCalendar = Calendar.getInstance();
    }
    else if ( e.getSource().equals(answerButton) ) offerAnswer();
    else if ( e.getSource().equals(clueButton )  ) {
        clueArea.setText(clueArea.getText() + qz.getQuestions().get(index).getClueText() + "\n");
        aA.setUsedClue(true);
        //JOptionPane.showMessageDialog(null, "hi");
        }
    else if ( e.getSource().equals(multiButton)  ) {            
        String[] answerOptions = qz.getQuestions().get(index).getAnswerOptions(3);
        JButton[] optionsButtons = new JButton[4];
        for(int j=0;j<4;j++){
            optionsButtons[j]=new JButton(answerOptions[j]);
            if(optionsButtons[j].getText().length()>13) 
                optionsButtons[j].setFont(TabbedQuiz.getDefaultFont().deriveFont(10));
            else optionsButtons[j].setFont(TabbedQuiz.getDefaultFont().deriveFont(15));
            if(j<2) optionsButtons[j].setBounds(295+211*j       , 170, 211, 55);
            else    optionsButtons[j].setBounds(295+211*(j-2)   , 226, 211, 55);
            optionsButtons[j].addMouseListener(this);
            optionsButtons[j].setName("optionsButton"+"["+j+"]");
            add(optionsButtons[j]);
            repaint();
        }
        aA.setMultipleChoice(true);
    }
    else if ( ( (JButton) e.getSource() ).getName().startsWith("optionsButton") ) {
        String answerOffered = ( (JButton) e.getSource() ).getText();
        answerArea.setText(answerOffered);
        offerAnswer();
    }
}

@Override
public void mouseEntered(MouseEvent e) {
    if(e.getSource()!=startButton && e.getSource().getClass().equals( answerButton.getClass()) ){
        ( (JButton) e.getSource() ).setBackground(Color.green);
    }if(index>0 && e.getSource()==startButton) remove(startButton);
}

@Override
public void mouseExited(MouseEvent e) {
    if(e.getSource()!=startButton && e.getSource().getClass().equals( answerButton.getClass()) ){
        ( (JButton) e.getSource() ).setBackground(UIManager.getColor("control"));
    }
}

@Override
public void mousePressed(MouseEvent e) {
}

@Override
public void mouseReleased(MouseEvent e) {
}
}

Answer 1

每个选项卡上都有一个面板，当用户执行点击按钮等操作时，面板会发生变化。

在我更改 GUI 上的任何内容之前，我会做 removeAll();

每当我看到这样的 cmets 时，我觉得您应该使用 Card Layout，这样您就不必担心所有这些问题。

Answer 2

如果使用布局管理器，您需要在移除或添加组件到容器后调用revalidate。然后你打电话给repaint。

您发布了很多代码，其中大部分与手头的问题完全无关，但另一方面，发布的代码不完整，无法编译，因此不是我们可以使用的代码测试。下次请尽量不要发布很多与问题无关的代码。尝试通过不断删减代码来隔离问题，如果仍然卡住，请发布一个最小的可兼容程序，我们可以自己研究、测试、运行和修改，sscce。

我浏览了您的一些 GUI 代码（天哪，不是全部！），并且在您踩到 Swing 绘画的地方存在一些严重的问题，例如 ProgressPanel.java 中的这段代码：

   public void paintComponent(Graphics g) {
      super.paintComponent(g);
      Graphics2D g2d = (Graphics2D) g;
      createAndShowGUI(g2d);
      // drawDifficultyChart(g2d, fontComboBox.getSelectedIndex());
   }

   private void createAndShowGUI(Graphics2D g2d) {
      JButton showChartButton = new JButton("Show new chart!");
      user = TabbedQuiz.getUser();
      showChartButton.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            try {
               if (categoryComboBox.getSelectedIndex() == 0
                     && difficultyComboBox.getSelectedIndex() != 0) {
                  drawDifficultyChart((Graphics2D) getGraphics(),
                        difficultyComboBox.getSelectedIndex());
               } else if (difficultyComboBox.getSelectedIndex() == 0
                     && categoryComboBox.getSelectedIndex() != 0) {
                  drawCategoryChart((Graphics2D) getGraphics(),
                        (String) categoryComboBox.getSelectedItem());
               } else
                  drawGeneralChart((Graphics2D) getGraphics(),
                        (String) categoryComboBox.getSelectedItem(),
                        difficultyComboBox.getSelectedIndex());
            } catch (NullPointerException e1) {
               JOptionPane.showMessageDialog(null, "Sign in first.");
            }
         }
      });
      showChartButton.setBounds(10, 90, 96, 26);
      showChartButton.setFont(font);
      add(showChartButton);
   }

问题是您正在从paint/paintComponent 方法中创建组件并将其添加到容器中，这是您永远不应该做的事情，而且肯定会弄乱程序的图形。

Answer 3

致有此问题的其他人：我最终解决了这个问题。 setVisible(false); setVisible(true);。随处可见。