有关JAVA中异常处理的错误

Question

我正在学习Java事件处理。 我编写了代码，但是在尝试从main方法调用类MyGUI的Constructor时显示错误。 请看看并向我解释以下错误。

错误：

No enclosing instance of type MyGUI is accessible. Must qualify the allocation 
with an enclosing instance of type MyGUI (e.g. x.new A() where x is an instance 
of MyGUI).

我的代码：

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

import javax.swing.*;


public class MyGUI extends JPanel {
    JButton button;
    JTextField textField;
    JRadioButton radioButton;

    MyGUI(){
    add(new JButton("Button"));
    add(new JTextField(10));
    add(new JRadioButton("RadioButton"));

    }


     class MyHandler implements ActionListener
    {

        @Override
        public void actionPerformed(ActionEvent e) {

            if(e.getSource()==button)
            {
                JOptionPane.showMessageDialog(null, "Button has been clicked");
            }
            else if(e.getSource()==textField)
            {
                JOptionPane.showMessageDialog(null, "TextField has been clicked");
            }
            else if(e.getSource()==radioButton)
            {
                JOptionPane.showMessageDialog(null, "RadioButton has been clicked");
            }

        }

    }

public static void main(String[]args)
{
    MyGUI gui=new MyGUI();

    MyHandler handler=new MyHandler();    //Error Shows on this statement
    gui.button.addActionListener(handler);


    JFrame frame=new JFrame("Its a frame");
    frame.add(gui);
    frame.setVisible(true);
    frame.setSize(500,500);
    frame.setLayout(new FlowLayout(FlowLayout.LEFT,10,10));
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);



}
}

Answer 1

main方法不是为MyGUI设置动作侦听器的MyGUI 。 将设置动作侦听器的代码移到MyGUI构造函数中。

您还需要将要创建的新组件分配给实例变量。

MyGUI(){
    button = new JButton("Button");
    textField = new JTextField(10);
    radioButton = new JRadioButton("RadioButton");

    add(button);
    add(textField);
    add(radioButton);

    MyHandler handler = new MyHandler();
    button.addActionListener(handler);
}