JTextArea 中 setText() 的机制?

2022-01-24 00:00:00 java swing jtextarea jframe settext

我尝试在运行时在我的 JTextArea 中显示一些文本.但是当我使用 setText 循环按顺序显示文本时，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 "Example 1", "Example 2",..,"Example 9".但它只显示一次Example 9"

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

谁能给我解释一下??

推荐答案

setText 就是这样做的，它将字段的文本设置"为您提供的值，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

如果您使用的是 Java 8，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());

(假设每次调用actionPerformed方法时都想替换文本，但仍然可以使用append)

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

根据评论的假设进行更新

我假设"您的意思是您希望每个 String 显示一小段时间，然后替换为下一个 String.

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的东西，比如循环，都会阻止 UI 更新.相反，您需要使用 Swing Timer 来安排定期回调，并在每次滴答时更改 UI.

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++;
                }
            });
        }

    }

}

看看 Swing 中的并发 和 如何使用 Swing 计时器 了解更多详情

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

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