值更改侦听器到JTextField [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，我需要点击回车键才能弹出消息框。我的代码有什么问题吗？

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);
        }       
    }
}

任何帮助都将不胜感激！

Any help would be appreciated!

推荐答案

为基础文档添加一个监听器，该监听器是为您自动创建的。

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 Massage",
          JOptionPane.ERROR_MESSAGE);
     }
  }
});

这篇关于值更改侦听器到JTextField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！