如何將 ActionListener 添加到在 for 循環中創建的多個按鈕？

Question

這是一個困難的問題，但是如何將ActionListener添加到我在 for 循環中創建的多個按鈕中？

到目前為止，這是我的代碼：

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class Loop extends JFrame {

    public Loop() {
        this.setSize(700, 300);
        this.setLocation(400, 300);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        JPanel jpanel = new JPanel();
        jpanel.setBackground(Color.CYAN);
        jpanel.setLayout(new GridLayout(0,6));
        
        JButton[] jButton = new JButton[6];
        String string[] = {"One","Two","Three","Four","Five","Six"};
        
        this.add(jpanel);
        int j=0;
        for(int i =0; i<jButton.length;i++) {
            while(j < 6) {
            jButton[i]= new JButton();
            jButton[i].setPreferredSize(new Dimension(50, 50));
            jButton[i].setText(string[j++]);
            
            jpanel.add(jButton[i]);
            jButton[i].addActionListener(new ActionListener() {

                public void actionPerformed(ActionEvent e) {
                    System.out.println("Works");
                }
            });
            }
        }   
    }
    
    public static void main(String[] args) {
        Loop myLoop = new Loop();
        myLoop.setVisible(true);
    }
}

（從代碼看來，在for循環中添加ActionListener會給所有按鈕提供相同的操作。問題是我希望每個按鈕的操作都不同）。

任何回應將不勝感激。

Answer 1

您可以創建ActionListener的列表或數組並將其傳遞給構造函數，例如

import java.awt.*;
import java.awt.event.ActionListener;
import java.util.List;

import javax.swing.*;

public class Loop extends JFrame {

    public Loop(java.util.List<ActionListener> listeners) {

        this.setSize(700, 300);
        this.setLocation(400, 300);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel jpanel = new JPanel();
        jpanel.setBackground(Color.CYAN);
        jpanel.setLayout(new GridLayout(0, 6));

        JButton[] jButton = new JButton[6];
        String[] string = {"One", "Two", "Three", "Four", "Five", "Six"};

        this.add(jpanel);
        int j = 0;

        for (int i = 0; i < jButton.length; i++) {
            while (j < 6) {
                jButton[i] = new JButton();
                jButton[i].setPreferredSize(new Dimension(50, 50));
                jButton[i].setText(string[j]);
                jpanel.add(jButton[i]);
                jButton[i].addActionListener(listeners.get(j));
                j++;
            }

        }

    }

    public static void main(String[] args) {
        java.util.List<ActionListener> listeners = List.of(
                e -> System.out.println("actionListener 1"),
                e -> System.out.println("actionListener 2"),
                e -> System.out.println("actionListener 3"),
                e -> System.out.println("actionListener 4"),
                e -> System.out.println("actionListener 5"),
                e -> System.out.println("actionListener 6")
        );
        Loop myLoop = new Loop(listeners);
        myLoop.setVisible(true);
    }
}

Answer 2

從代碼中可以看出，在 for 循環中添加 ActionListener 會給所有按鈕提供相同的操作。

你是對的。 您正在創建一個實現ActionListener接口的匿名 class 。 但是，每個JButton都分配有該 class 的單獨實例。

將相同的單個實例分配給不同的JButton沒有任何問題。 在actionPerformed方法的代碼中，您可以通過檢查ActionEvent參數來識別激活了哪個JButton 。

ActionEvent包含一個動作命令字符串以及source ，在您的情況下，它是被激活的實際JButton 。

就個人而言，我會讓您的Loop class 實現ActionListener並在actionPerformed方法中確定從action command激活了哪個JButton 。 下面的代碼演示。

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class Loop extends JFrame implements ActionListener {

    public Loop() {
        this.setSize(700, 300);
        this.setLocation(400, 300);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel jpanel = new JPanel();
        jpanel.setBackground(Color.CYAN);
        jpanel.setLayout(new GridLayout(0, 6));

        JButton[] jButton = new JButton[6];
        String string[] = {"One", "Two", "Three", "Four", "Five", "Six"};

        this.add(jpanel);

        for (int i = 0; i < jButton.length; i++) {
            jButton[i] = new JButton(string[i]);
            jButton[i].setPreferredSize(new Dimension(50, 50));
            jpanel.add(jButton[i]);
            jButton[i].addActionListener(this);
        }
    }

    public void actionPerformed(ActionEvent event) {
        String actionCommand = event.getActionCommand();
        switch (actionCommand) {
            case "One":
                break;
            case "Two":
                break;
            case "Three":
                break;
            case "Four":
                break;
            case "Five":
                break;
            case "Six":
                break;
            default:
        }
    }

    public static void main(String[] args) {
        Loop myLoop = new Loop();
        myLoop.setVisible(true);
    }
}

默認情況下，操作命令被分配了JButton的文本，但您可以通過setActionCommand方法分配不同的值。

Answer 3

你可以這樣做：

import java.awt.*;
import java.util.stream.Stream;
import javax.swing.*;
    
    @SuppressWarnings("serial")
    public class Loop extends JFrame {
    
        public Loop() {
    
            final JPanel jpanel = new JPanel();
            /**/         jpanel.setBackground(Color.CYAN);
            /**/         jpanel.setLayout(new GridLayout(0, 6));
    
            this.add    (jpanel);
    
            Stream.of("One", "Two", "Three", "Four", "Five", "Six")
            .forEach(text -> {
                final JButton button = new JButton(text);
                /**/          button.setPreferredSize(new Dimension(50, 50));
                /**/          button.addActionListener((e) -> {System.out.println("Button " + text + " pressed");});
                jpanel.add   (button);
            });
    
            this.setPreferredSize(new Dimension(700, 300));
            this.setLocation(400, 300);
            this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    
            this.pack();
            this.setResizable(false);
            this.setVisible(true);
        }
    
        public static void main(final String[] args) {
            SwingUtilities.invokeLater(() -> new Loop());
        }
    }

Answer 4

您需要某種方式來識別哪個 Button，但您可以使用 1 個共享偵聽器，如下所示。

請注意使用SwingUtilities.invokeLater(...)在正確的線程上執行。

import java.awt.*;
import java.awt.event.ActionListener;
import java.util.stream.Stream;
import javax.swing.*;

@SuppressWarnings("serial")
public class Loop extends JFrame {

    public Loop() {

        final JPanel jpanel = new JPanel();
        /**/         jpanel.setBackground(Color.CYAN);
        /**/         jpanel.setLayout(new GridLayout(0, 6));

        this.add    (jpanel);

        final ActionListener oneSharedListener = (e) -> System.out.println("Button " + e.getActionCommand() + " pressed");

        Stream.of("One", "Two", "Three", "Four", "Five", "Six")
        .forEach(text -> {
            final JButton button = new JButton(text);
            /**/          button.setPreferredSize(new Dimension(50, 50));
            /**/          button.addActionListener(oneSharedListener);
            /**/          button.setActionCommand(text);
            jpanel.add   (button);
        });

        this.setPreferredSize(new Dimension(700, 300));
        this.setLocation(400, 300);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        this.pack();
        this.setResizable(false);
        this.setVisible(true);
    }

    public static void main(final String[] args) {
        SwingUtilities.invokeLater(() -> new Loop());
    }
}