随机字符串生成 - 一个接一个地生成两个给出相同的结果

I have a simple piece of code:

我有一段简单的代码:

public string GenerateRandomString()
        {
            string randomString = string.Empty;
            Random r = new Random();
            for (int i = 0; i < length; i++)
                randomString += chars[r.Next(chars.Length)];

            return randomString;
        }
p