I was looking for a more specific answer, where I want to control the format of the random string and came across this post. For example: license plates (of cars) have a specific format (per country) and I wanted to created random license plates. I decided to write my own extension method of Random for this. (this is in order to reuse the same Random object, as you could have doubles in multi-threading scenarios). I created a gist (https://gist.github.com/SamVanhoutte/808845ca78b9c041e928), but will also copy the extension class here:

void Main()
{
    Random rnd = new Random();
    rnd.GetString("1-###-000").Dump();
}

public static class RandomExtensions
{
    public static string GetString(this Random random, string format)
    {
        // Based on http://stackoverflow.com/questions/1344221/how-can-i-generate-random-alphanumeric-strings-in-c
        // Added logic to specify the format of the random string (# will be random string, 0 will be random numeric, other characters remain)
        StringBuilder result = new StringBuilder();
        for(int formatIndex = 0; formatIndex < format.Length ; formatIndex++)
        {
            switch(format.ToUpper()[formatIndex])
            {
                case '0': result.Append(getRandomNumeric(random)); break;
                case '#': result.Append(getRandomCharacter(random)); break;
                default : result.Append(format[formatIndex]); break;
            }
        }
        return result.ToString();
    }

    private static char getRandomCharacter(Random random)
    {
        string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        return chars[random.Next(chars.Length)];
    }

    private static char getRandomNumeric(Random random)
    {
        string nums = "0123456789";
        return nums[random.Next(nums.Length)];
    }
}

不是100%确定，因为我没有测试这里的每个选项，但在我测试的选项中，这个是最快的。用秒表计时，它显示9-10滴答，所以如果速度比安全更重要，试试这个:

 private static Random random = new Random(); 
 public static string Random(int length)
     {   
          var stringChars = new char[length];

          for (int i = 0; i < length; i++)
              {
                  stringChars[i] = (char)random.Next(0x30, 0x7a);                  
                  return new string(stringChars);
              }
     }

尝试将两部分结合起来:独特(序列、计数器或日期)和随机

public class RandomStringGenerator
{
    public static string Gen()
    {
        return ConvertToBase(DateTime.UtcNow.ToFileTimeUtc()) + GenRandomStrings(5); //keep length fixed at least of one part
    }

    private static string GenRandomStrings(int strLen)
    {
        var result = string.Empty;

        using (var gen = new RNGCryptoServiceProvider())
        {
            var data = new byte[1];

            while (result.Length < strLen)
            {
                gen.GetNonZeroBytes(data);
                int code = data[0];
                if (code > 48 && code < 57 || // 0-9
                    code > 65 && code < 90 || // A-Z
                    code > 97 && code < 122   // a-z
                )
                {
                    result += Convert.ToChar(code);
                }
            }

            return result;
        }
    }

    private static string ConvertToBase(long num, int nbase = 36)
    {
        const string chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; //if you wish to make the algorithm more secure - change order of letter here

        // check if we can convert to another base
        if (nbase < 2 || nbase > chars.Length)
            return null;

        int r;
        var newNumber = string.Empty;

        // in r we have the offset of the char that was converted to the new base
        while (num >= nbase)
        {
            r = (int)(num % nbase);
            newNumber = chars[r] + newNumber;
            num = num / nbase;
        }
        // the last number to convert
        newNumber = chars[(int)num] + newNumber;

        return newNumber;
    }
}

测试:

    [Test]
    public void Generator_Should_BeUnigue1()
    {
        //Given
        var loop = Enumerable.Range(0, 1000);
        //When
        var str = loop.Select(x=> RandomStringGenerator.Gen());
        //Then
        var distinct = str.Distinct();
        Assert.AreEqual(loop.Count(),distinct.Count()); // Or Assert.IsTrue(distinct.Count() < 0.95 * loop.Count())
    }

我的代码的主要目标是:

弦的分布几乎是均匀的(不关心微小的偏差，只要它们很小) 它为每个参数集输出超过几十亿个字符串。如果您的PRNG只生成20亿(31位熵)不同的值，那么生成8个字符的字符串(约47位熵)是没有意义的。 它是安全的，因为我希望人们使用它作为密码或其他安全令牌。

第一个属性是通过对字母大小取一个64位值的模来实现的。对于小字母(例如问题中的62个字符)，这导致了可以忽略不计的偏差。第二个和第三个属性是通过使用RNGCryptoServiceProvider而不是System.Random来实现的。

using System;
using System.Security.Cryptography;

public static string GetRandomAlphanumericString(int length)
{
    const string alphanumericCharacters =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
        "abcdefghijklmnopqrstuvwxyz" +
        "0123456789";
    return GetRandomString(length, alphanumericCharacters);
}

public static string GetRandomString(int length, IEnumerable<char> characterSet)
{
    if (length < 0)
        throw new ArgumentException("length must not be negative", "length");
    if (length > int.MaxValue / 8) // 250 million chars ought to be enough for anybody
        throw new ArgumentException("length is too big", "length");
    if (characterSet == null)
        throw new ArgumentNullException("characterSet");
    var characterArray = characterSet.Distinct().ToArray();
    if (characterArray.Length == 0)
        throw new ArgumentException("characterSet must not be empty", "characterSet");

    var bytes = new byte[length * 8];
    var result = new char[length];
    using (var cryptoProvider = new RNGCryptoServiceProvider())
    {
        cryptoProvider.GetBytes(bytes);
    }
    for (int i = 0; i < length; i++)
    {
        ulong value = BitConverter.ToUInt64(bytes, i * 8);
        result[i] = characterArray[value % (uint)characterArray.Length];
    }
    return new string(result);
}

不使用Random的解决方案:

var chars = Enumerable.Repeat("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789", 8);

var randomStr = new string(chars.SelectMany(str => str)
                                .OrderBy(c => Guid.NewGuid())
                                .Take(8).ToArray());

在查看了其他答案并考虑了CodeInChaos的评论，以及CodeInChaos仍然有偏见(尽管较少)的答案之后，我认为需要一个最终的终极剪切和粘贴解决方案。所以在更新我的答案时，我决定全力以赴。

For an up to date version of this code, please visit the new Hg repository on Bitbucket: https://bitbucket.org/merarischroeder/secureswiftrandom. I recommend you copy and paste the code from: https://bitbucket.org/merarischroeder/secureswiftrandom/src/6c14b874f34a3f6576b0213379ecdf0ffc7496ea/Code/Alivate.SolidSwiftRandom/SolidSwiftRandom.cs?at=default&fileviewer=file-view-default (make sure you click the Raw button to make it easier to copy and make sure you have the latest version, I think this link goes to a specific version of the code, not the latest).

更新说明:

Relating to some other answers - If you know the length of the output, you don't need a StringBuilder, and when using ToCharArray, this creates and fills the array (you don't need to create an empty array first) Relating to some other answers - You should use NextBytes, rather than getting one at a time for performance Technically you could pin the byte array for faster access.. it's usually worth it when your iterating more than 6-8 times over a byte array. (Not done here) Use of RNGCryptoServiceProvider for best randomness Use of caching of a 1MB buffer of random data - benchmarking shows cached single bytes access speed is ~1000x faster - taking 9ms over 1MB vs 989ms for uncached. Optimised rejection of bias zone within my new class.

问题的最终解决方案:

static char[] charSet =  "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".ToCharArray();
static int byteSize = 256; //Labelling convenience
static int biasZone = byteSize - (byteSize % charSet.Length);
public string GenerateRandomString(int Length) //Configurable output string length
{
    byte[] rBytes = new byte[Length]; //Do as much before and after lock as possible
    char[] rName = new char[Length];
    SecureFastRandom.GetNextBytesMax(rBytes, biasZone);
    for (var i = 0; i < Length; i++)
    {
        rName[i] = charSet[rBytes[i] % charSet.Length];
    }
    return new string(rName);
}

但是你需要我的新(未经测试的)类:

/// <summary>
/// My benchmarking showed that for RNGCryptoServiceProvider:
/// 1. There is negligable benefit of sharing RNGCryptoServiceProvider object reference 
/// 2. Initial GetBytes takes 2ms, and an initial read of 1MB takes 3ms (starting to rise, but still negligable)
/// 2. Cached is ~1000x faster for single byte at a time - taking 9ms over 1MB vs 989ms for uncached
/// </summary>
class SecureFastRandom
{
    static byte[] byteCache = new byte[1000000]; //My benchmark showed that an initial read takes 2ms, and an initial read of this size takes 3ms (starting to raise)
    static int lastPosition = 0;
    static int remaining = 0;

    /// <summary>
    /// Static direct uncached access to the RNGCryptoServiceProvider GetBytes function
    /// </summary>
    /// <param name="buffer"></param>
    public static void DirectGetBytes(byte[] buffer)
    {
        using (var r = new RNGCryptoServiceProvider())
        {
            r.GetBytes(buffer);
        }
    }

    /// <summary>
    /// Main expected method to be called by user. Underlying random data is cached from RNGCryptoServiceProvider for best performance
    /// </summary>
    /// <param name="buffer"></param>
    public static void GetBytes(byte[] buffer)
    {
        if (buffer.Length > byteCache.Length)
        {
            DirectGetBytes(buffer);
            return;
        }

        lock (byteCache)
        {
            if (buffer.Length > remaining)
            {
                DirectGetBytes(byteCache);
                lastPosition = 0;
                remaining = byteCache.Length;
            }

            Buffer.BlockCopy(byteCache, lastPosition, buffer, 0, buffer.Length);
            lastPosition += buffer.Length;
            remaining -= buffer.Length;
        }
    }

    /// <summary>
    /// Return a single byte from the cache of random data.
    /// </summary>
    /// <returns></returns>
    public static byte GetByte()
    {
        lock (byteCache)
        {
            return UnsafeGetByte();
        }
    }

    /// <summary>
    /// Shared with public GetByte and GetBytesWithMax, and not locked to reduce lock/unlocking in loops. Must be called within lock of byteCache.
    /// </summary>
    /// <returns></returns>
    static byte UnsafeGetByte()
    {
        if (1 > remaining)
        {
            DirectGetBytes(byteCache);
            lastPosition = 0;
            remaining = byteCache.Length;
        }

        lastPosition++;
        remaining--;
        return byteCache[lastPosition - 1];
    }

    /// <summary>
    /// Rejects bytes which are equal to or greater than max. This is useful for ensuring there is no bias when you are modulating with a non power of 2 number.
    /// </summary>
    /// <param name="buffer"></param>
    /// <param name="max"></param>
    public static void GetBytesWithMax(byte[] buffer, byte max)
    {
        if (buffer.Length > byteCache.Length / 2) //No point caching for larger sizes
        {
            DirectGetBytes(buffer);

            lock (byteCache)
            {
                UnsafeCheckBytesMax(buffer, max);
            }
        }
        else
        {
            lock (byteCache)
            {
                if (buffer.Length > remaining) //Recache if not enough remaining, discarding remaining - too much work to join two blocks
                    DirectGetBytes(byteCache);

                Buffer.BlockCopy(byteCache, lastPosition, buffer, 0, buffer.Length);
                lastPosition += buffer.Length;
                remaining -= buffer.Length;

                UnsafeCheckBytesMax(buffer, max);
            }
        }
    }

    /// <summary>
    /// Checks buffer for bytes equal and above max. Must be called within lock of byteCache.
    /// </summary>
    /// <param name="buffer"></param>
    /// <param name="max"></param>
    static void UnsafeCheckBytesMax(byte[] buffer, byte max)
    {
        for (int i = 0; i < buffer.Length; i++)
        {
            while (buffer[i] >= max)
                buffer[i] = UnsafeGetByte(); //Replace all bytes which are equal or above max
        }
    }
}

对于历史-我对这个答案的旧解决方案，使用随机对象:

    private static char[] charSet =
      "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".ToCharArray();

    static rGen = new Random(); //Must share, because the clock seed only has Ticks (~10ms) resolution, yet lock has only 20-50ns delay.
    static int byteSize = 256; //Labelling convenience
    static int biasZone = byteSize - (byteSize % charSet.Length);
    static bool SlightlyMoreSecurityNeeded = true; //Configuration - needs to be true, if more security is desired and if charSet.Length is not divisible by 2^X.
    public string GenerateRandomString(int Length) //Configurable output string length
    {
      byte[] rBytes = new byte[Length]; //Do as much before and after lock as possible
      char[] rName = new char[Length];
      lock (rGen) //~20-50ns
      {
          rGen.NextBytes(rBytes);

          for (int i = 0; i < Length; i++)
          {
              while (SlightlyMoreSecurityNeeded && rBytes[i] >= biasZone) //Secure against 1/5 increased bias of index[0-7] values against others. Note: Must exclude where it == biasZone (that is >=), otherwise there's still a bias on index 0.
                  rBytes[i] = rGen.NextByte();
              rName[i] = charSet[rBytes[i] % charSet.Length];
          }
      }
      return new string(rName);
    }

性能:

securefastrrandom -第一次运行= ~9-33ms。听不清。持续:5毫秒(有时高达13毫秒)超过10,000次迭代，单次平均迭代= 1.5微秒。注意:通常需要2个缓存刷新，但偶尔需要8个缓存刷新——这取决于有多少单个字节超出了偏置区域 随机-第一次运行= ~0-1ms。听不清。正在进行:5毫秒超过10,000次迭代。单次平均迭代= 0.5微秒。速度差不多。

还可以看看:

https://bitbucket.org/merarischroeder/number-range-with-no-bias/src https://stackoverflow.com/a/45118325/887092

这些联系是另一种方法。缓冲可以添加到这个新的代码库中，但最重要的是探索不同的方法来消除偏差，并对速度和利弊进行基准测试。