如何截取进入Java Swing JTextField的键盘笔触? [英] How to intercept keyboard strokes going to Java Swing JTextField?

问题描述

JTextField是一个计算器显示，被初始化为零，并且以十进制数字形式显示以0或00123等开头的十进制数字是一种不好的形式.NetBeansSwing JFrame中的数字按钮(0..9)使用append()[下方]来删除前导零，但用户可能更喜欢键盘而不是鼠标，并且还需要处理非数字字符.

The JTextField is a calculator display initialized to zero and it is bad form to display a decimal number with a leading 0 like 0123 or 00123. The numeric buttons (0..9) in a NetBeans Swing JFrame use append() [below] to drop the leading zeros, but the user may prefer the keyboard to a mouse, and non-numeric characters also need to be handled.

private void append(String s) {
    if (newEntry) {
        newEntry = false;
        calcDisplay.setText(s);
    } else if (0 != Float.parseFloat(calcDisplay.getText().toString())) {
        calcDisplay.setText(calcDisplay.getText().toString() + s);
    }
}

推荐答案

您可以通过添加自定义KeyListener来限制输入到JTextField的字符.这是一个简单的例子来说明这个想法:

You could restrict the characters input to the JTextField by adding a custom KeyListener. Here is a quick example to demonstrate the idea:

myTextField.addKeyListener(new KeyAdapter() {
  @Override
  public void keyTyped(KeyEvent e) {
    char c = e.getKeyChar();
    if (!Character.isDigit(c)) {
      e.consume(); // Stop the event from propagating.
    }
  }
});

当然，您需要考虑特殊键(如Delete)和组合键(如CTRL-C)，因此KeyListener应该更复杂.甚至可能有免费的实用程序可以为您完成大多数繁琐的工作.

Of course, you need to consider special keys like Delete and combinations like CTRL-C, so your KeyListener should be more sophisticated. There are probably even freely available utilities to do most of the grunt work for you.

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