随着聊天的进行，如何使聊天程序向下滚动？

Question

I'm making a simple chat GUI. I've come into a problem where my program isn't scrolling down as the chat moves along. I'm also unsure about how to add a scroll bar/pane to the program, without messing everything up by putting my main text area into a panel and destroying the look of the interface. How do I adjust the main chat box, without screwing it up and making it look ugly by putting the chatBox in a JPanel. I'll post all of my code below.

MainGUI class:

package coltGUI;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.ScrollPaneConstants;
import javax.swing.UIManager;

public class MainGUI implements ActionListener {

    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception e) {
            e.printStackTrace();
        }

        MainGUI gui = new MainGUI();
        gui.display();
    }

    JButton sendMessage;
    JTextField messageBox;
    JTextArea chatBox;

    public void display() {

        JFrame frame = new JFrame("Colt Chat");
        JPanel southPanel = new JPanel();

        frame.getContentPane().add(BorderLayout.SOUTH, southPanel);
        southPanel.setBackground(Color.BLUE);
        southPanel.setLayout(new GridBagLayout());

        messageBox = new JTextField(30);
        sendMessage = new JButton("Send Message");
        chatBox = new JTextArea();
        chatBox.setEditable(false);
        frame.getContentPane().add(BorderLayout.CENTER, chatBox);

        chatBox.setLineWrap(true);

        GridBagConstraints left = new GridBagConstraints();
        left.anchor = GridBagConstraints.WEST;
        GridBagConstraints right = new GridBagConstraints();
        right.anchor = GridBagConstraints.EAST;
        right.weightx = 2.0;

        southPanel.add(messageBox, left);
        southPanel.add(sendMessage, right);

        sendMessage.addActionListener(this);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        frame.setSize(470, 300);
    }

    public void actionPerformed(ActionEvent event) {
        if (messageBox.getText().length() < 1) {
            // do nothing 
        } else {
            chatBox.append(messageBox.getText() + "\n");
            messageBox.setText("");
        }
    }
}

Answer 1

Just add the text area to a JScrollPane and then add the scrollpane to the frame. There is no need for a panel.

//frame.getContentPane().add(BorderLayout.CENTER, chatBox);
frame.add(new JScrollPane(chatBox), BorderLayout.CENTER);

Note that constraints should be specified as the second parameter of the add(...) method, not the first.

Also, since JDK5, you don't need to use getContentPane(), the frame.add(..) method will do this for you.

If you want automatic scrolling you can check out Text Area Scrolling .

Answer 2

First you need to wrap chatBox in a JScrollPane like this:

frame.add(new JScrollPane(chatBox), BorderLayout.CENTER);

Second after appending the message to chatBox you need to force it to scroll to the end which can be done with the following:

chatBox.setCaretPosition(chatBox.getDocument().getLength());