C#正则表达式只保留字母a-z A-Z 0-9

记录去除二维码中的空格和特殊字符。

正则表达式只保留字母a-z A-Z 0-9 ，代码如下：

 private void button1_Click(object sender, EventArgs e)
        {
            string str = "SSDSD#SDS>SSS..SAFHSJA D";
            string brorad = str.Trim();//需要筛选的目标字符串  
            textBox1.Text = restr(brorad);
        }
        public string restr(string brorad)
        {
            string pattern = "[A-Za-z0-9]";//只需要英文字母a-z A-Z 0-9 
            string strRet = "";
            MatchCollection results = Regex.Matches(brorad, pattern);
            foreach (var v in results)
            {
                strRet += v.ToString();
            }
            return strRet;
        }

运行结果：SSDSDSDSSSSSAFHSJAD