C#自定义函数NetxtString生成随机字符串

/// <summary>
/// 生成随机字符串
/// </summary>
/// <param name="random">Random</param>
/// <param name="size">字符串长度</param>
/// <param name="lowerCase">字符串是小写</param>
/// <returns>随机字符串</returns>
public static string NetxtString(this Random random, int size, bool lowerCase)
{
  StringBuilder _builder = new StringBuilder(size);
  int _startChar = lowerCase ? 97 : 65;//65 = A / 97 = a
  for (int i = 0; i < size; i++)
 _builder.Append((char)(26 * random.NextDouble() + _startChar));
  return _builder.ToString();
}

static void Main(string[] args)
{
  try
  {
 Random _random = new Random();
 for (int i = 0; i < 10; i++)
 {
   Console.WriteLine(_random.NetxtString(4, false));
 }
  }
  catch (Exception ex)
  {
 Console.WriteLine(ex.Message);
  }
  finally
  {
 Console.ReadLine();
  }
}

/// <summary>
/// 0~9 A~Z字符串
/// </summary>
public static string RandomString_09AZ = "0123456789ABCDEFGHIJKMLNOPQRSTUVWXYZ";
/// <summary>
/// 依据指定字符串来生成随机字符串
/// </summary>
/// <param name="random">Random</param>
/// <param name="randomString">指定字符串</param>
/// <param name="size">字符串长度</param>
/// <param name="lowerCase">字符串是小写</param>
/// <returns>随机字符串</returns>
public static string NetxtString(this Random random, string randomString, int size, bool lowerCase)
{
  string _nextString = string.Empty;
  if (random != null && !string.IsNullOrEmpty(randomString))
  {
 StringBuilder _builder = new StringBuilder(size);
 int _maxCount = randomString.Length - 1;
 for (int i = 0; i < size; i++)
 {
   int _number = random.Next(0, _maxCount);
   _builder.Append(randomString[_number]);
 }
 _nextString = _builder.ToString();
  }
  return lowerCase ? _nextString.ToLower() : _nextString.ToUpper();
}

static void Main(string[] args)
{
  try
  {
 Random _random = new Random();
 string _ramdomString = RandomToolV2.RandomString_09AZ;
 for (int i = 0; i < 20; i++)
 {
   // Console.WriteLine(_random.NetxtString(4, false));
   Console.WriteLine(_random.NetxtString(_ramdomString, 4, false));
 }
  }
  catch (Exception ex)
  {
 Console.WriteLine(ex.Message);
  }
  finally
  {
 Console.ReadLine();
  }
}