在JTextArea中setText（）的机制？ [英] Mechanisms of setText() in JTextArea?

问题描述

我尝试在运行时在 JTextArea 中显示一些文本。但是当我使用循环 setText 按顺序显示文本时，它只显示最后一个循环的文本
这是我的代码：

I try to show some text in my JTextArea in runtime. But when I use a loop of setText to show text in order, it only show the text of the last loop Here is my code:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
 for (int i=0;i<10;i++)
     jTextArea1.setText("Example "+i);
}                                        

我希望它显示示例1， 示例2，..，示例9。但它只显示一次示例9

I want it to show "Example 1", "Example 2",..,"Example 9". But it only show one time "Example 9"

任何人都可以为我解释一下吗？

Anyone can explain it for me??

推荐答案

setText 就是这样，它将字段设置为值你提供的，删除所有以前的内容。

setText does just that, it "sets the text" of field to the value your provide, removing all previous content.

你想要的是 JTextArea＃append

What you want is JTextArea#append

如果您使用的是Java 8，则另一个选项可能是 StringJoiner

If you're using Java 8, another option might be StringJoiner

StringJoiner joiner = new StringJoiner(", ");
for (int i = 0; i < 10; i++) {
    joiner.add("QUang " + i);
}
jTextArea1.setTexy(joiner.toString());

（假设您想在每次 actionPerformed 方法，但你仍然可以使用追加）

(assuming you want to replace the text each time the actionPerformed method is called, but you can still use append)

根据假设进行更新评论

我假设你的意思是你想要显示每个字符串一段时间，然后用下一个 String 替换。

I "assume" you mean you want each String to be displayed for a short period of time and then replaced with the next String.

Swing是一个单线程环境，所以任何阻塞事件调度线程（如循环）将阻止UI更新。相反，您需要使用Swing Timer 来定期调度回调，并在每个tick上更改UI。例如，

Swing is a single threaded environment, so anything that blocks the Event Dispatching Thread, like loops, will prevent the UI from been updated. Instead, you need to use a Swing Timer to schedule a callback at regular intervals and make change the UI on each tick, for example.

import java.awt.BorderLayout;
import java.awt.EventQueue;
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.Timer;
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();
                }

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

    public class TestPane extends JPanel {

        private String[] messages = {
            "Example 1",
            "Example 2",
            "Example 3",
            "Example 4",
            "Example 5",
            "Example 6",
            "Example 7",
            "Example 8",
            "Example 9",
        };

        private JTextArea ta;
        private int index;

        private Timer timer;

        public TestPane() {
            setLayout(new BorderLayout());
            ta = new JTextArea(1, 20);
            add(new JScrollPane(ta));

            JButton btn = new JButton("Start");
            btn.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    if (timer.isRunning()) {
                        timer.stop();
                    }
                    index = 0;
                    timer.start();
                }
            });
            add(btn, BorderLayout.SOUTH);

            timer = new Timer(500, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    if (index < messages.length) {
                        ta.setText(messages[index]);
                    } else {
                        timer.stop();
                    }
                    index++;
                }
            });
        }

    }

}

查看 Swing中的并发和如何使用Swing Timers 获取更多详细信息

Have a look at Concurrency in Swing and How to use Swing Timers for more details

这篇关于在JTextArea中setText（）的机制？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！