//生成签名 private static string GenerateSign(Dictionary<string, string> data) { var list = data.ToList(); list.Sort((a, b) => string.Compare(a.Key, b.Key, StringComparison.Ordinal)); var builder = new StringBuilder(); foreach (var item in list) { if (!string.IsNullOrEmpty(item.Value)) { builder.Append(item.Key).Append('=').Append(item.Value).Append('&'); } } builder.Append("key=").Append(WECHAT_PAY_KEY); return MD5Helper.MD5(builder.ToString()).ToUpper(); }上面的c#代码，MD5Helper类怎么实现

MD5Helper类的实现可能类似于以下代码：

using System.Security.Cryptography;
using System.Text;

public static class MD5Helper
{
    public static string MD5(string input)
    {
        using (var md5 = MD5.Create())
        {
            var inputBytes = Encoding.UTF8.GetBytes(input);
            var hashBytes = md5.ComputeHash(inputBytes);
            var hashStringBuilder = new StringBuilder();
            foreach (var hashByte in hashBytes)
            {
                hashStringBuilder.Append(hashByte.ToString("x2"));
            }
            return hashStringBuilder.ToString();
        }
    }
}

这个类中，我们使用了C#自带的MD5类来计算字符串的MD5哈希值，并将结果转换为16进制字符串。