using System.Text;
using System.Collections;
public static class WebUtility
{
// Fields
private static char[] _htmlEntityEndingChars = new char[] { ';', '&' };
private const char HIGH_SURROGATE_START = '\ud800';
private const char LOW_SURROGATE_END = '\udfff';
private const char LOW_SURROGATE_START = '\udc00';
private const int UNICODE_PLANE00_END = 0xffff;
private const int UNICODE_PLANE01_START = 0x10000;
private const int UNICODE_PLANE16_END = 0x10ffff;
private const int UnicodeReplacementChar = 0xfffd;

private static void ConvertSmpToUtf16(uint smpChar, out char leadingSurrogate, out char trailingSurrogate)
{
    int num = ((int) smpChar) - 0x10000;
    leadingSurrogate = (char) ((num / 0x400) + 0xd800);
    trailingSurrogate = (char) ((num % 0x400) + 0xdc00);
}

private static int HexToInt(char h)
{
    if ((h >= '0') && (h <= '9'))
    {
        return (h - '0');
    }
    if ((h >= 'a') && (h <= 'f'))
    {
        return ((h - 'a') + 10);
    }
    if ((h >= 'A') && (h <= 'F'))
    {
        return ((h - 'A') + 10);
    }
    return -1;
}

private static char IntToHex(int n)
{
    if (n <= 9)
    {
        return (char) (n + 0x30);
    }
    return (char) ((n - 10) + 0x41);
}

private static bool IsUrlSafeChar(char ch)
{
    if ((((ch >= 'a') && (ch <= 'z')) || ((ch >= 'A') && (ch <= 'Z'))) || ((ch >= '0') && (ch <= '9')))
    {
        return true;
    }
    switch (ch)
    {
    case '(':
    case ')':
    case '*':
    case '-':
    case '.':
    case '_':
    case '!':
        return true;
    }
    return false;
}

public static string UrlEncode(string value)
{
    if (value == null)
    {
        return null;
    }
    byte[] bytes = Encoding.UTF8.GetBytes(value);
    return Encoding.UTF8.GetString(UrlEncode(bytes, 0, bytes.Length, false));
}

private static bool ValidateUrlEncodingParameters(byte[] bytes, int offset, int count)
{
    if ((bytes == null) && (count == 0))
    {
        return false;
    }
    if (bytes == null)
    {
        //throw new ArgumentNullException("bytes");
    }
    if ((offset < 0) || (offset > bytes.Length))
    {
        //throw new ArgumentOutOfRangeException("offset");
    }
    if ((count < 0) || ((offset + count) > bytes.Length))
    {
        //throw new ArgumentOutOfRangeException("count");
    }
    return true;
}

private static byte[] UrlEncode(byte[] bytes, int offset, int count)
{
    if (!ValidateUrlEncodingParameters(bytes, offset, count))
    {
        return null;
    }
    int num = 0;
    int num2 = 0;
    for (int i = 0; i < count; i++)
    {
        char ch = (char) bytes[offset + i];
        if (ch == ' ')
        {
            num++;
        }
        else if (!IsUrlSafeChar(ch))
        {
            num2++;
        }
    }
    if ((num == 0) && (num2 == 0))
    {
        return bytes;
    }
    byte[] buffer = new byte[count + (num2 * 2)];
    int num4 = 0;
    for (int j = 0; j < count; j++)
    {
        byte num6 = bytes[offset + j];
        char ch2 = (char) num6;
        if (IsUrlSafeChar(ch2))
        {
            buffer[num4++] = num6;
        }
        else if (ch2 == ' ')
        {
            buffer[num4++] = 0x2b;
        }
        else
        {
            buffer[num4++] = 0x25;
            buffer[num4++] = (byte) IntToHex((num6 >> 4) & 15);
            buffer[num4++] = (byte) IntToHex(num6 & 15);
        }
    }
    return buffer;
}

private static byte[] UrlEncode(byte[] bytes, int offset, int count, bool alwaysCreateNewReturnValue)
{
    byte[] buffer = UrlEncode(bytes, offset, count);
    if ((alwaysCreateNewReturnValue && (buffer != null)) && (buffer == bytes))
    {
        return (byte[]) buffer.Clone();
    }
    return buffer;
}

public static byte[] UrlEncodeToBytes(byte[] value, int offset, int count)
{
    return UrlEncode(value, offset, count, true);
}

}

==================================================================================

public static string ToUrlEncode(string strCode)
{
StringBuilder sb = new StringBuilder();
byte[] byStr = System.Text.Encoding.UTF8.GetBytes(strCode); //默认是System.Text.Encoding.Default.GetBytes(str)
System.Text.RegularExpressions.Regex regKey = new System.Text.RegularExpressions.Regex("^[A-Za-z0-9]+$");
for (int i = 0; i < byStr.Length; i++)
{
string strBy = Convert.ToChar(byStr[i]).ToString();
if (regKey.IsMatch(strBy))
{
//是字母或者数字则不进行转换
sb.Append(strBy);
}
else
{
sb.Append(@"%" + Convert.ToString(byStr[i], 16));
}
}
return (sb.ToString());
}