System.Text.Encoder.Convert C# (CSharp) Method

        public virtual unsafe void Convert(char* chars, int charCount,
                                             byte* bytes, int byteCount, bool flush,
                                             out int charsUsed, out int bytesUsed, out bool completed)
        {
            // Validate input parameters
            if (bytes == null || chars == null)
                throw new ArgumentNullException(bytes == null ? "bytes" : "chars",
                    Environment.GetResourceString("ArgumentNull_Array"));
                if (charCount < 0 || byteCount < 0)
                throw new ArgumentOutOfRangeException((charCount<0 ? "charCount" : "byteCount"),
                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));

            // Get ready to do it
            charsUsed = charCount;

            // Its easy to do if it won't overrun our buffer.
            while (charsUsed > 0)
            {
                if (GetByteCount(chars, charsUsed, flush) <= byteCount)
                {
                    bytesUsed = GetBytes(chars, charsUsed, bytes, byteCount, flush);
                    completed = (charsUsed == charCount &&
                        (m_fallbackBuffer == null || m_fallbackBuffer.Remaining == 0));
                    return;
                }

                // Try again with 1/2 the count, won't flush then 'cause won't read it all
                flush = false;
                charsUsed /= 2;
            }

            // Oops, we didn't have anything, we'll have to throw an overflow
            throw new ArgumentException(Environment.GetResourceString("Argument_ConversionOverflow"));
        }
    }

        public static string UrlEncode(string str, string encode)
        {
            int factor = 0;

            if (encode == "UTF-8")
            {
                factor = 3;
            }
            if (encode == "GB2312")
            {
                factor = 2;
            }
            //不需要编码的字符

            string okChar = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789.";

            System.Text.Encoder encoder = System.Text.Encoding.GetEncoding(encode).GetEncoder();
            char[] c1 = str.ToCharArray();
            System.Text.StringBuilder sb = new System.Text.StringBuilder();
            //一个字符一个字符的编码

            for (int i = 0; i < c1.Length; i++)
            {
                //不需要编码

                if (okChar.IndexOf(c1[i]) > -1)
                {
                    sb.Append(c1[i]);
                }
                else
                {
                    byte[] c2 = new byte[factor];
                    int    charUsed, byteUsed; bool completed;

                    encoder.Convert(c1, i, 1, c2, 0, factor, true, out charUsed, out byteUsed, out completed);

                    foreach (byte b in c2)
                    {
                        if (b != 0)
                        {
                            sb.AppendFormat("%{0:X}", b);
                        }
                    }
                }
            }
            return(sb.ToString().Trim());
        }