正如评论中提到的(以及我输入的另一个答案)，您需要注册一个事件处理程序来捕获文本框上的 keydown 或 keypress 事件.这是因为 TextChanged 仅在 TextBox 失去焦点时触发

As mentioned in a comment (and another answer as I typed) you need to register an event handler to catch the keydown or keypress event on a text box. This is because TextChanged is only fired when the TextBox loses focus

下面的正则表达式可以让你匹配那些你想要允许的字符

The below regex lets you match those characters you want to allow

Regex regex = new Regex(@"[0-9+-/*()]");
MatchCollection matches = regex.Matches(textValue);

而这恰恰相反，会捕获不允许的字符

and this does the opposite and catches characters that aren't allowed

Regex regex = new Regex(@"[^0-9^+^-^/^*^(^)]");
MatchCollection matches = regex.Matches(textValue);

我不会假设会有一个匹配项，因为有人可以将文本粘贴到文本框中.在这种情况下捕获 textchanged

I'm not assuming there'll be a single match as someone could paste text into the textbox. in which case catch textchanged

textBox1.TextChanged += new TextChangedEventHandler(textBox1_TextChanged);
private void textBox1_TextChanged(object sender, EventArgs e)
{
    Regex regex = new Regex(@"[^0-9^+^-^/^*^(^)]");
    MatchCollection matches = regex.Matches(textBox1.Text);
    if (matches.Count > 0) {
       //tell the user
    }
}

并验证单个按键

textBox1.KeyPress += new KeyPressEventHandler(textBox1_KeyPress);
private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
    // Check for a naughty character in the KeyDown event.
    if (System.Text.RegularExpressions.Regex.IsMatch(e.KeyChar.ToString(), @"[^0-9^+^-^/^*^(^)]"))
    {
        // Stop the character from being entered into the control since it is illegal.
        e.Handled = true;
    }
}