Java Swing - 从处理程序类重绘

Question

所以我先把我的两个类的代码放在这里。

SquareSimp.java

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

public class SquareSimp
{

    public static void main( String[] args )
    {
        FilledFrame frame = new FilledFrame();

        frame.setVisible( true );
    }
}

class FilledFrame extends JFrame
{
    int size = 400;

    public FilledFrame()
    {
        JButton butSmall   = new JButton("Small");
        JButton butMedium  = new JButton("Medium");
        JButton butLarge   = new JButton("Large");
        JButton butMessage = new JButton("Say Hi!");

        SquarePanel panel = new SquarePanel(this);
        JPanel butPanel = new JPanel();

        butSmall.addActionListener(new ButtonHandler1(this, 200){
            @Override
            public void actionPerformed(ActionEvent actionEvent) {
                size = 200;
                panel.repaint();
            }
        });

        butMedium.addActionListener(new ButtonHandler1(this, this.size){
            @Override
            public void actionPerformed(ActionEvent actionEvent) {
                size = 300;
                panel.repaint();
            }
        });

        butLarge.addActionListener(new ButtonHandler1(this, this.size){
            @Override
            public void actionPerformed(ActionEvent actionEvent) {
                size = 400;
                panel.repaint();
            }
        });



        butPanel.add(butSmall);
        butPanel.add(butMedium);
        butPanel.add(butLarge);
        butPanel.add(butMessage);
        add(butPanel, BorderLayout.NORTH);
        add(panel, BorderLayout.CENTER);

        setSize( size+100, size+100 );
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        // Exercise 2.
        //Anonymous implementations of listeners are very efficient when you do not need to pass parameters to the
        // constructor of the implemented listener.
        butMessage.addActionListener(new ActionListener()
                // An anonymous function. Creates an actionListener that shows a dialog.
        {
            @Override
            public void actionPerformed(ActionEvent e)
            {
                JOptionPane.showMessageDialog(null, "Hiiii");
            }
        });

    }

}

class SquarePanel extends JPanel
{
    FilledFrame theApp;

    SquarePanel(FilledFrame app)
    {
        theApp = app;
    }

    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        g.setColor(Color.green);
        g.fillRect(20, 20, theApp.size, theApp.size);
    }
}

ButtonHandler1.java

package Lab2;

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
// This is a class whose object will handle the event.
public class ButtonHandler1 implements ActionListener{
    private FilledFrame theApp;
    private int theSize;
    ButtonHandler1(FilledFrame app, int size){
        theApp = app;
        theSize = size;
    }

    public void actionPerformed(ActionEvent actionEvent) {
    }

}

到目前为止，一切正常，这很棒。但是，作为要求，我被要求为每个类制作一个按钮处理程序。有人可以向我解释一下我的 buttonHandler 到底在做什么吗？我觉得与其制作匿名函数并覆盖 actionPerformed 事件，不如用更好的方法来完成它（在 buttonhandler 类中创建事件并根据按下的按钮从那里影响大小）。我不知道该怎么做，所以任何解释的帮助都会很棒！

非常感谢！

布兰登

Answer 1

*Listener 的任何处理程序都用于处理由正在侦听的对象生成的@​​987654322@。在主程序中，您似乎有几个按钮可以改变窗口的大小。

如果你的类实现了 buttonHandler，你什么也没做，因为你的 actionPerformed 方法什么也没做。

而anonymous classes 是一种可接受的实现监听器的方式。但是，我更喜欢使用inner classes，因为它们更干净（恕我直言）并且仍然可以访问enclosing class 的state。

这是您的处理程序类的外观：

// This is a class whose object will handle the event.
class ButtonHandler1 implements ActionListener {
   private FilledFrame theApp;
   private int         theSize;

   ButtonHandler1(FilledFrame app, int size) {
      theApp = app;
      theSize = size;
   }

   public void actionPerformed(ActionEvent actionEvent) {
      theApp.size = theSize;
      theApp.repaint();
   }
}

以下是将处理程序添加到按钮的调用。

      butSmall.addActionListener(new ButtonHandler1(this, 200));
      butMedium.addActionListener(new ButtonHandler1(this, 300));
      butLarge.addActionListener(new ButtonHandler1(this, 400));

Answer 2

我不确定我是否理解了这个问题，但有两种方法可以重构您的代码：

1. 完全删除您的ButtonHandler1 类并实现匿名类中的所有逻辑：

    //FilledFrame.java

    butSmall.addActionListener(new ActionListener(){
                @Override
                public void actionPerformed(ActionEvent actionEvent) {
                    FilledFrame.this.size = 200;
                    panel.repaint();
                }
            });

1. 您可以在 FilledFrame 类中添加一些 getter 和 setter 方法，并在 ButtonHandler1.actionPerformed 中调用这些方法来实现那里的逻辑，如下所示：

    package Lab2;

    import javax.swing.*;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    // This is a class whose object will handle the event.
    public class ButtonHandler1 implements ActionListener{
        private FilledFrame theApp;
        private int theSize;
        ButtonHandler1(FilledFrame app, int size){
            theApp = app;
            theSize = size;
        }

        public void actionPerformed(ActionEvent actionEvent) {
            theApp.setSizeMember(200); //do not use theApp.setSize(), create a method with a different name
            theApp.getSquarePanel().repaint();
        }

    }

我将在 FilledFrame 上创建 getter/setter 留给你。

Answer 3

ButtonHandler1 并没有真正使用，因为传递给它的参数从未使用过，并且在构造它时会覆盖其单个方法。
所以这个：

     butSmall.addActionListener(new ButtonHandler1(this, 200){
            @Override
            public void actionPerformed(ActionEvent actionEvent) {
                size = 200;
                panel.repaint();
            }
      });

可以不用构造ButtonHandler1：

    butSmall.addActionListener(new ActionListener(){
        @Override
        public void actionPerformed(ActionEvent actionEvent) {
            size = 200;
            panel.repaint();
        }
    });

或者使用 lambda 表达式：

    butSmall.addActionListener(actionEvent -> {
        size = 200;
        panel.repaint();
    });

您可以通过多种方式实现您想要的功能。根据您写的内容，您可以像这样定义ButtonHandler1：

class ButtonHandler1 implements ActionListener{
    private final FilledFrame theApp;
    private final int theSize;
    ButtonHandler1(FilledFrame app, int size){
        theApp = app;
        theSize = size;
    }

    @Override
    public void actionPerformed(ActionEvent actionEvent) {
        theApp.size = theSize; //better use a setter in FilledFrame
        theApp.repaint();
    }
}

并像这样使用它：

    butSmall.addActionListener(new ButtonHandler1(this, 200));

    butMedium.addActionListener(new ButtonHandler1(this, 300));

    butLarge.addActionListener(new ButtonHandler1(this, 400));

使ButtonHandler1 成为FilledFrame 中的内部类让事情变得更简单：

class ButtonHandler1 implements ActionListener{
    private final int theSize;
    ButtonHandler1(int size){
        theSize = size;
    }

    @Override
    public void actionPerformed(ActionEvent actionEvent) {
        size = theSize;
        repaint();
    }
}

使用它：

    butSmall.addActionListener(new ButtonHandler1(200));

    butMedium.addActionListener(new ButtonHandler1(300));

    butLarge.addActionListener(new ButtonHandler1(400));