DocumentListener 出错 [英] Error with DocumentListener

问题描述

我有一个 JTextField，我希望将其限制为 15 个字符.问题是当我输入超过 15 个字符时，它会出错.我怎样才能解决这个问题?我必须使用其他对象吗?

I have a JTextField that I want to be limited to fifteen characters. The problem is that when I type over 15 characters, it errors. How can i fix this? Do I have to use some other object?

错误:线程AWT-EventQueue-0"中的异常java.lang.IllegalStateException:尝试在通知中发生变化

The error: Exception in thread "AWT-EventQueue-0" java.lang.IllegalStateException: Attempt to mutate in notification

 final int maxNicknameLength = 15;
 final JTextField nickname = new JTextField(1); //Max length: 15
 DocumentListener docListen = new DocumentListener() {
      public void changedUpdate(DocumentEvent e) {
           lengthCheck(e, nickname, maxNicknameLength);
      }

      public void insertUpdate(DocumentEvent e) {
           lengthCheck(e, nickname, maxNicknameLength);
      }

      public void removeUpdate(DocumentEvent e) {
           lengthCheck(e, nickname, maxNicknameLength);
      }
      public void lengthCheck (DocumentEvent e, JTextField txt, int max) {
           if (txt.getText().length() > max)
                txt.setText(txt.getText().substring(0, max));
      }    
 };
 nickname.getDocument().addDocumentListener(docListen);

推荐答案

使用 DocumentFilter，而不是 DocumentListener.到侦听器触发时，文档已经更新.过滤器将阻止文档更新.

Use a DocumentFilter, not a DocumentListener. By the time the listener fires the Document has already been updated. A filter will prevent the document from being updated.

请参阅:实现文档过滤器工作示例可以满足您的需求.

See: Implementing a Document Filter for a working example that does what your want.

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