JTextField 的值更改侦听器 [英] Value Change Listener to JTextField

问题描述

我希望在用户更改文本字段中的值后立即显示消息框.目前，我需要按回车键才能弹出消息框.我的代码有问题吗?

I want the message box to appear immediately after the user changes the value in the textfield. Currently, I need to hit the enter key to get the message box to pop out. Is there anything wrong with my code?

textField.addActionListener(new java.awt.event.ActionListener() {
    public void actionPerformed(java.awt.event.ActionEvent e) {

        if (Integer.parseInt(textField.getText())<=0){
            JOptionPane.showMessageDialog(null,
                    "Error: Please enter number bigger than 0", "Error Message",
                    JOptionPane.ERROR_MESSAGE);
        }       
    }
}

任何帮助将不胜感激！

推荐答案

为底层 Document 添加一个监听器，它会自动为你创建.

Add a listener to the underlying Document, which is automatically created for you.

// Listen for changes in the text
textField.getDocument().addDocumentListener(new DocumentListener() {
  public void changedUpdate(DocumentEvent e) {
    warn();
  }
  public void removeUpdate(DocumentEvent e) {
    warn();
  }
  public void insertUpdate(DocumentEvent e) {
    warn();
  }

  public void warn() {
     if (Integer.parseInt(textField.getText())<=0){
       JOptionPane.showMessageDialog(null,
          "Error: Please enter number bigger than 0", "Error Message",
          JOptionPane.ERROR_MESSAGE);
     }
  }
});

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