在 Java 中为 CustomButton 创建 ActionEvent 对象

Question

对于硬件分配，我们应该创建一个自定义按钮来熟悉 Swing 和响应事件。我们还打算让这个按钮成为一个事件源，这让我很困惑。我有一个 ArrayList 来跟踪将注册以侦听我的 CustomButton 的侦听器。我感到困惑的是如何通知听众。我的老师暗示我尝试做一个通知和重写 actionPerformed ，但后来我不确定如何创建一个 ActionEvent 对象查看构造函数文档。来源、id、字符串都让我困惑。任何帮助将不胜感激。

代码：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.List;
import java.util.ArrayList;

public class CustomButton 
{
    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                CustomButtonFrame frame = new CustomButtonFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setVisible(true);
            }
        });
    }

    public void addActionListener(ActionListener al)
    {
        listenerList.add(al);
    }

    public void removeActionListener(ActionListener al)
    {
        listenerList.remove(al);
    }

    public void actionPerformed(ActionEvent e) 
    {
        System.out.println("Button Clicked!");
    }

    private void notifyListeners()
    {
        ActionEvent event = new ActionEvent(CONFUSED HERE!!!!;
        for (ActionListener action : listenerList) {
            action.actionPerfomed(event);
        }
    }

    List<ActionListener> listenerList = new ArrayList<ActionListener>();
}

class CustomButtonFrame extends JFrame
{
    // constructor for CustomButtonFrame
    public CustomButtonFrame()
    {
        setTitle("Custom Button");
        CustomButtonSetup buttonSetup = new CustomButtonSetup();
        this.add(buttonSetup);
        this.pack();
    }
}

class CustomButtonSetup extends JComponent 
{
    public CustomButtonSetup()
    {
        ButtonAction buttonClicked = new ButtonAction();
        this.addMouseListener(buttonClicked);
    }

    // because frame includes borders and insets, use this method
    public Dimension getPreferredSize()
    {
        return new Dimension(200, 200);
    }

    public void paintComponent(Graphics g)
    {
        Graphics2D g2 = (Graphics2D) g;

        // first triangle coords
        int x[] = new int[TRIANGLE_SIDES];
        int y[] = new int[TRIANGLE_SIDES];
        x[0] = 0;   y[0] = 0;
        x[1] = 200; y[1] = 0;
        x[2] = 0;   y[2] = 200;
        Polygon firstTriangle = new Polygon(x, y, TRIANGLE_SIDES);

        // second triangle coords
        x[0] = 0;   y[0] = 200;     
        x[1] = 200; y[1] = 200;
        x[2] = 200; y[2] = 0;
        Polygon secondTriangle = new Polygon(x, y, TRIANGLE_SIDES);

        g2.drawPolygon(firstTriangle);
        g2.setColor(firstColor);
        g2.fillPolygon(firstTriangle);

        g2.drawPolygon(secondTriangle);
        g2.setColor(secondColor);
        g2.fillPolygon(secondTriangle);

        // draw rectangle 10 pixels off border
        int s1[] = new int[RECT_SIDES];
        int s2[] = new int[RECT_SIDES];
        s1[0] = 5;    s2[0] = 5;
        s1[1] = 195;  s2[1] = 5;
        s1[2] = 195;  s2[2] = 195;
        s1[3] = 5;    s2[3] = 195;
        Polygon rectangle = new Polygon(s1, s2, RECT_SIDES);
        g2.drawPolygon(rectangle);
        g2.setColor(thirdColor);
        g2.fillPolygon(rectangle);  
    }

    private class ButtonAction implements MouseListener {
        public void mousePressed(MouseEvent e)
        {
            System.out.println("Click!");
            firstColor = Color.GRAY;
            secondColor = Color.WHITE;

            repaint();
        }

        public void mouseReleased(MouseEvent e)
        {
            System.out.println("Released!");
            firstColor = Color.WHITE;
            secondColor = Color.GRAY;
            repaint();
        }

        public void mouseEntered(MouseEvent e)
        {}

        public void mouseExited(MouseEvent e)
        {}

        public void mouseClicked(MouseEvent e)
        {}
    }

    public static final int TRIANGLE_SIDES = 3;
    public static final int RECT_SIDES = 4;
    private Color firstColor = Color.WHITE;
    private Color secondColor = Color.DARK_GRAY;
    private Color thirdColor = Color.LIGHT_GRAY;
}

Answer 1

阅读有关 ActionEvent 的文档。有一节是关于它的构造函数的，请阅读每个参数的含义。

对于您的情况，适用的代码将如下所示：

int uniqueId = System.currentTimeMillis().intValue();
String commandName = ""; //it can be like "show" or "hide" or whatever else; 
                         //you can get this string with getActionCommand() method
                         //and make some actions based on its value
                         //... but you don't need it now
ActionEvent event = new ActionEvent(this, uniqueId, commandName);

Answer 2

总体思路是：

• 您维护一组侦听器。
• 如果您必须通知侦听器（发生了事件），则可以迭代侦听器集合并在每个侦听器（在您的情况下为 ActionListener）上调用适当的方法。

我没有看到 ActionListener 和 ActionEvent 的声明。根据您的模式，ActionEvent 很可能会有一种表示实际事件的状态字段，因此它有一个类似 public ActionEvent(int value) 等的构造函数。侦听器接收 ActionEvent，查看 ActionEvent 对象内部，然后了解为什么他收到通知。

编辑

从其他人的回答中我刚刚了解到 ActionListener 和 ActionEvent 是 AWT 类。所以看看他们的java文档，我的其余答案应该仍然有效。

编辑2

最简单的构造函数是这个：

public ActionEvent(Object source, int id, String command);

源是触发事件的对象，因此在您的情况下，最有可能是按钮。 id 标识事件的类型。从 ActionEvent 或 AWTEvent 的静态字段中进行选择。该命令是您可以放置​​有关事件的附加信息的区域。