必须要引入这个命明空间using System.Text.RegularExpressions;

private void button1_Click(object sender, EventArgs e)        {            string str;            str = textBox1.Text;            if (Regex.IsMatch(str, @"[0-9]")&&Regex.IsMatch(str, @"[a-z]")&& Regex.IsMatch(str, @"[A-Z]"))             //只能按顺序输入数字-小写字母-大写字母@"[0-9][a-z][A-Z]"<->@"[0-9]" + @"[a-z]" + @"[A-Z]"               textBox2.Text = "格式正确";            else                textBox2.Text ="格式错误";                         Console.ReadLine();                 }