在 Java 中使用 JFrame 的侦听器

Question

我现在正在学习 ActionListeners 的基础知识，我一直在这里寻求帮助，但不能完全find/figure我做错了什么。

我有一个 class（客户端）实现了主调用：

...
public static void main(String[] args) {

    Myframe test = new Myframe();

    N = test.setVisible(); // N is an integer

...
}

然后是我框架中的代码：

public class test extends JFrame {

    private JPanel contentPane;
    private int N;

    public int setVisible(){

        this.setVisible(true);
        return N;

    }

    /**
     * Create the frame.
     */
    public test() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);

        JButton btnOk = new JButton("OK");
        btnOk.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {

                N=5;
                dispose();

            }
        });
        contentPane.add(btnOk, BorderLayout.SOUTH);
    }

}

问题是：程序在继续运行之前不等待按下按钮，N 导致一些垃圾值，从而产生错误。我应该怎么做才能让它在不休眠线程的情况下正确处理它？

Answer 1

解决此问题的一些方法。使用 JDialog - 默认提供模态阻塞，Listener 机制 - 稍后用值回调，或者让你的代码阻塞

JDialog

public class test extends JDialog {
    ...    
    private int N;

    public int setVisible() {
        this.setVisible(true);
        return N;
    }

    public test() {
        super(null, ModalityType.APPLICATION_MODAL); 
        // <== pass parent window here if you have one, you don't seem to.. 
        ...
    }

阻塞示例

使用java.util.concurrent.CountDownLatch

代码

public class test extends JFrame {
    ....    
    private CountDownLatch latch;
    private int N;

    public int setVisible() throws InterruptedException{

        latch = new CountDownLatch(1);
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                setVisible(true);
            }
        });

        latch.await();   // <== block until countDown called
        return N;
    }

    public test() {           
        ...
        btnOk.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {

                N=5;
                latch.countDown();   <== will unblock await() call
                dispose();

            }
        });
        ...
    }

}

听众

public class test extends JFrame {
    ... 
    private Listener listener;

    public static interface Listener {
        void setN(int n);
    }

    public void setVisible(Listener listener) throws InterruptedException {
        this.listener = listener;   // <== save reference to listener
        setVisible(true);
    }

    public test() {
        ...
        btnOk.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {

                listener.setN(5);  // <== call listener
                dispose();

            }
        });
    }

Answer 2

使用模态 JDialog 而不是 JFrame，它们被设计成在它们可见的地方阻塞，直到它们被关闭...

import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }


    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JDialog frame = new JDialog();
                TestPane testPane = new TestPane();
                frame.setTitle("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(testPane);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

                System.out.println("The value was - " + testPane.getValue());
            }
        });
    }

    public class TestPane extends JPanel {

        private int n;

        public TestPane() {
            JButton btnOk = new JButton("OK");
            btnOk.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent arg0) {

                    n = 5;
                    SwingUtilities.windowForComponent(TestPane.this).dispose();

                }
            });
        }

    }

    public int getValue() {
        return n;
    }

}

查看 How to Make Dialogs 了解更多详情

在 Java 中使用 JFrame 的侦听器

Listener using JFrame in Java

java

swing

actionlistener

JDialog

阻塞示例

听众