我正在使用WindowBuilder在Java中创建一些聊天功能。我的GUI类创建了一个线程，我希望从该线程中更新超类的TextArea。我创建线程的原因是我希望能够中断子类内部的代码。
我的问题是我无法从子类的线程中追加到超类的TextArea。
我尝试将代码缩减为基本要点：
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JMenu;
import javax.swing.GroupLayout;
import javax.swing.GroupLayout.Alignment;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class SSCCE {
private JFrame frmRoom;
private final static String newline = "\r\n";
private JTextField textField;
private JScrollPane scrollPane;
private JTextArea textArea;
/**
* Launch the application.
*/
public static void main(String[] args) {
try {
} catch (Throwable e) {
e.printStackTrace();
}
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
SSCCE window = new SSCCE();
window.frmRoom.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the application.
*/
public SSCCE() {
initialize();
}
/**
* Initialize the contents of the frame.
*/
private void initialize() {
frmRoom = new JFrame();
frmRoom.setTitle("Test");
frmRoom.setBounds(100, 100, 450, 300);
frmRoom.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JMenuBar menuBar = new JMenuBar();
frmRoom.setJMenuBar(menuBar);
JMenu mnButton1 = new JMenu("Button 1");
menuBar.add(mnButton1);
JMenuItem mntmButton2 = new JMenuItem("Button 2");
mntmButton2.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
Thread t = new Thread(new SSCCESub());
SwingUtilities.invokeLater(t);
//t.start();
//Neither of the above work.
}
});
mnButton1.add(mntmButton2);
textField = new JTextField();
scrollPane = new JScrollPane();
textArea = new JTextArea();
textArea.setEditable(false);
scrollPane.setViewportView(textArea);
GroupLayout groupLayout = new GroupLayout(frmRoom.getContentPane());
groupLayout.setHorizontalGroup(
groupLayout.createParallelGroup(Alignment.LEADING)
.addComponent(scrollPane, GroupLayout.DEFAULT_SIZE, 434, Short.MAX_VALUE)
.addGroup(Alignment.TRAILING, groupLayout.createSequentialGroup()
.addComponent(textField, GroupLayout.PREFERRED_SIZE, 434, Short.MAX_VALUE)
.addGap(0))
);
groupLayout.setVerticalGroup(
groupLayout.createParallelGroup(Alignment.LEADING)
.addGroup(groupLayout.createSequentialGroup()
.addComponent(scrollPane, GroupLayout.DEFAULT_SIZE, 214, Short.MAX_VALUE)
.addComponent(textField, GroupLayout.PREFERRED_SIZE, 28, GroupLayout.PREFERRED_SIZE))
);
frmRoom.getContentPane().setLayout(groupLayout);
}
private void addLineToTextArea(String line) {
System.out.println("Tried calling a superclass method in order to append to the TextArea");
textArea.append(line + newline);
}
private static class SSCCESub extends SSCCE implements Runnable {
public void run() {
super.textArea.append("This won't be visible" + newline); //TODO This is what my question is about.
super.addLineToTextArea("This won't be visible");
System.out.println("This should be visible");
return;
}
}
}
答案 0 :(得分：1)
简单的答案是：不要使用继承来尝试促进子对象与父对象之间的通信。那不是继承的目的，不是继承的工作原理（正如您所发现的）。而是使用组合-使用构造函数或方法参数将object1的实例传递给object2，并调用公共方法传递信息。
因此，您的第二个类可以具有一个采用SSCCE参数的构造函数，允许您传入该参数，然后设置SSCCE字段，这可以使您调用当前SSCCE对象的公共方法。
接下来，修复此问题后，您的代码将运行在Swing线程规则之外-您只应在Swing事件线程上更改Swing组件。请阅读Lesson: Concurrency in Swing
更多详细的答案来了......
例如，假设您想将Swing GUI与套接字挂钩，以进行简单的聊天通信。我们可以创建一个新的GUI类，称为SSCCE2，类似....
json使用一个公共方法，例如import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.Socket;
import javax.swing.*;
@SuppressWarnings("serial")
public class SSCCE2 extends JPanel {
private static final int GAP = 4;
private Action submitAction = new SubmitAction("Submit");
private JTextField textField = new JTextField(40);
private JTextArea textArea = new JTextArea(20, 40);
private JButton submitButton = new JButton(submitAction);
private PrintWriter printWriter = null;
private ChatWorker chatWorker = null;
public SSCCE2(Socket socket) throws IOException {
printWriter = new PrintWriter(socket.getOutputStream());
chatWorker = new ChatWorker(this, socket);
chatWorker.execute();
textArea.setFocusable(false);
JScrollPane scrollPane = new JScrollPane(textArea);
scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
textField.setAction(submitAction);
JPanel bottomPanel = new JPanel();
bottomPanel.setLayout(new BoxLayout(bottomPanel, BoxLayout.LINE_AXIS));
bottomPanel.add(textField);
bottomPanel.add(submitButton);
setBorder(BorderFactory.createEmptyBorder(GAP, GAP, GAP, GAP));
setLayout(new BorderLayout(GAP, GAP));
add(scrollPane);
add(bottomPanel, BorderLayout.PAGE_END);
}
// Action (acts as an ActionListener) that gets text from
// JTextField and puts it into JTextArea
// And also sends it via PrintWriter to the Socket
private class SubmitAction extends AbstractAction {
public SubmitAction(String name) {
super(name);
}
@Override
public void actionPerformed(ActionEvent e) {
String text = textField.getText();
textField.selectAll();
// send this to the socket for chatting....
if (printWriter != null) {
printWriter.println(text);
}
textArea.append(text);
textArea.append("\n");
}
}
// public method to allow outside objects to append to the JTextArea
public void append(String text) {
textArea.append(text);
textArea.append("\n");
}
}
，该方法允许外部类追加到JTextArea，然后我们将其实例传递到需要的地方，这里：public void append(String text)通过传递{{1} }。然后我们的ChatWorker可以调用公共方法：
chatWorker = new ChatWorker(this, socket);