java - 无法从 jpanel 中删除组件

Question

我重构了我的代码以生成一个最小的、可重现的示例。

问题 - 我无法从面板中删除卡(我已在出现问题的代码中进行了注释，请参阅“ClearCardEventListener”类)。

完整代码如下。

在运行程序之前，您需要下载一个图像并将其添加到资源文件夹 = https://ibb.co/MNccGS0

1. 运行程序
2. 点击“添加卡片”按钮(这将在面板上添加 2 颗红心图像图标)

3. 点击“清除卡”按钮(这就是问题所在，我无法从面板中删除卡)

   package debug.debug;
   
   import java.awt.Insets;
   import java.awt.event.ActionEvent;
   import java.awt.event.ActionListener;
   import java.util.ArrayList;
   import java.util.Arrays;
   import java.util.Collections;
   import java.util.List;
   
   import javax.swing.ImageIcon;
   import javax.swing.JButton;
   import javax.swing.JFrame;
   import javax.swing.JLabel;
   import javax.swing.JPanel;
   
   public class App extends JFrame {
       public static void main(String[] args) {
           App app = new App();
   
           Insets insets = app.getInsets();
           app.setSize(300 + insets.left + insets.right,
               300 + insets.top + insets.bottom);
       }
   
       JPanel panel;
       JButton clearCardButton;
       JButton addCardButton;
   
       List<Card> playerCards = new ArrayList<Card> ();
   
       Deck deck = new Deck();
   
       public App() {
           setTitle("BlackJack Game");
           setVisible(true);
           setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
           setLocationRelativeTo(null);
           panel = new JPanel();
           add(panel);
           panel.setLayout(null);
           addCardButton = new JButton("Add card");
           clearCardButton = new JButton("Clear card");
   
           panel.add(addCardButton);
           panel.add(clearCardButton);
   
           addCardButton.addActionListener(new AddCardEventListener(this, this.deck));
           clearCardButton.addActionListener(new ClearCardEventListener(this, this.deck));
   
           addCardButton.setBounds(150, 50, addCardButton.getPreferredSize().width, addCardButton.getPreferredSize().height);
           clearCardButton.setBounds(150, 100, clearCardButton.getPreferredSize().width, clearCardButton.getPreferredSize().height);
   
       }
   
       public JPanel getPanel() {
           return panel;
       }
   
       public void addPlayerCard(Card card) {
           playerCards.add(card);
       }
   
       public List<Card> getPlayerCards() {
           return playerCards;
       }
   
       public List<JLabel> getPlayerCardLabels() {
   
           List<JLabel> playerCardLabels = new ArrayList<JLabel> ();
   
           for (int i = 0; i<this.getPlayerCards().size(); i++) {
               playerCardLabels.add(this.getPlayerCards().get(i).getCardLabel());
   
           }
   
           return playerCardLabels;
       }
   
   }
   
   class AddCardEventListener implements ActionListener {
   
       private App app;
       private Deck deck;
   
       AddCardEventListener(App app, Deck deck) {
           this.app = app;
           this.deck = deck;
       }
   
       public void actionPerformed(ActionEvent arg0) {
   
           // Player gets a card
           app.addPlayerCard(deck.getCard());
   
           // Display that player's card
           app.getPanel()
               .add(app.getPlayerCards().get(0).getCardLabel()).setBounds(0, 0, 72, 96);
   
       }
   
   }
   
   class ClearCardEventListener implements ActionListener {
   
       private App app;
       private Deck deck;
   
       ClearCardEventListener(App app, Deck deck) {
           this.app = app;
           this.deck = deck;
       }
   
       public void actionPerformed(ActionEvent arg0) {
   
           System.out.println("DEBUG: " + app.getPlayerCards().get(0).getCardLabel());
   
           /***
            * 
            * NOT ABLE TO REMOVE CARD, WHY ???
            * 
            */
   
           app.getPlayerCards().get(0).getCardLabel().setIcon(null);
           app.getPlayerCards().get(0).getCardLabel().revalidate();
           app.getPlayerCards().get(0).getCardLabel().repaint();
   
           app.getPanel().remove(app.getPlayerCards().get(0).getCardLabel());
   
       }
   
   }
   
   class Card {
   
       private String suit;
       private String rank;
       private int value;
   
       public void setSuit(String suit) {
           this.suit = suit;
       }
       public void setRank(String rank) {
           this.rank = rank;
       }
       public void setValue(int value) {
           this.value = value;
       }
       public String getSuit() {
           return suit;
       }
       public String getRank() {
           return rank;
       }
       public int getValue() {
           return value;
       }
   
       // Hardcoded for debugging, so every card image is a 2 of hearts
       public JLabel getCardLabel() {
           return new JLabel(new ImageIcon(getClass()
               .getResource("/cards/2h.png")));
       }
   }
   
   class Deck {
   
       private final String RANKS[] = {
           "Ace",
           "Deuce",
           "Three",
           "Four",
           "Five",
           "Six",
           "Seven",
           "Eight",
           "Nine",
           "Ten",
           "Jack",
           "Queen",
           "King"
       };
       private final String SUITS[] = {
           "Spades",
           "Hearts",
           "Diamonds",
           "Clubs"
       };
   
       private Card[] deck;
       static private int cardPosition = 0;
   
       public Deck() {
           deck(); // Create the deck
           shuffle(); // shuffle the deck
       }
   
       public Card[] deck() {
           deck = new Card[52];
   
           for (int x = 0; x<deck.length; x++) {
               String rankTemp = RANKS[x % 13];
               String suitTemp = SUITS[x / 13];
               deck[x] = new Card();
               deck[x].setRank(rankTemp);
               deck[x].setSuit(suitTemp);
               deck[x].setValue((x % 13) + 1);
               if (deck[x].getValue() > 10)
                   deck[x].setValue(10);
               else if (deck[x].getValue() == 1)
                   deck[x].setValue(11);
           }
   
           return deck;
       }
   
       public void shuffle() {
           Collections.shuffle(Arrays.asList(deck()));
       }
   
       public Card[] getDeck() {
           return deck;
       }
   
       public Card getCard() {
           return deck[cardPosition++];
       }
   
   }
   

Answer 1

问题#1

每次调用 Card#getCardLabel 时，它都会创建一个新的 JLabel 实例...

class Card {

    // Hardcoded for debugging, so every card image is a 2 of hearts
    public JLabel getCardLabel() {
        return new JLabel(new ImageIcon(getClass()
            .getResource("/cards/2h.png")));
    }
}

这意味着当您这样做时...

app.getPanel().add(app.getPlayerCards().get(0).getCardLabel()).setBounds(0, 0, 72, 96);

还有...

System.out.println("DEBUG: " + app.getPlayerCards().get(0).getCardLabel());

还有...

app.getPlayerCards().get(0).getCardLabel().setIcon(null);
app.getPlayerCards().get(0).getCardLabel().revalidate();
app.getPlayerCards().get(0).getCardLabel().repaint();

app.getPanel().remove(app.getPlayerCards().get(0).getCardLabel());

每次调用实际上都是创建一个 JLabel 的新实例，因此屏幕上的实例与您尝试修改的实例无关。

因此，您的 Card#getCardLabel 应该仅创建一个 JLabel 一次，这也称为“延迟加载”...

class Card {

    private JLabel label;

    //...

    // Hardcoded for debugging, so every card image is a 2 of hearts
    public JLabel getCardLabel() {
        if (label == null) {
            // Simple image for demonstration purposes
            BufferedImage img = new BufferedImage(100, 150, BufferedImage.TYPE_INT_RGB);
            Graphics2D g2d = img.createGraphics();
            g2d.setColor(Color.WHITE);
            g2d.fillRect(0, 0, 100, 150);
            g2d.setColor(Color.RED);
            g2d.drawLine(0, 0, 100, 150);
            g2d.drawLine(100, 0, 0, 150);
            g2d.dispose();

            label = new JLabel(new ImageIcon(img));
        }

        return label;
    }
}

问题#2

Swing 是惰性的(好吧，它是“优化的”)，这意味着添加或删除组件本身不会触发布局或绘制过程。这样做是为了让您可以对 UI 进行大量更改，而不是让它尝试更新每个更改，这会非常慢。

这意味着当您添加或删除组件时，您还应该调用 repaint 来触发新的绘制 channel (我还建议 revalidate，但您'没有使用任何布局管理器，所以它不会为你做任何事情)

app.getPanel().remove(app.getPlayerCards().get(0).getCardLabel());
app.getPanel().repaint();